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Home away from home - Objective mapping of high-risk source areas for plant introductions
Diversity and Distributions
Abstract
Prevention is the best way to slow the escalation of problems associated with biological invasions. Screening of potential introductions is widely applied for assessing the risk of species becoming invasive. Despite advances in the understanding of the determinants of invasiveness, screening still relies heavily on assessments of the potential of species to ‘fit in’ to the broad environmental conditions of a target region. Most screening systems ask whether species are native to, or are known to be naturalized or invasive in, regions with ‘similar’ climatic/environmental conditions to the target region. The level of similarity required to make the species a high‐risk introduction is generally not specified. This paper describes a protocol for making such assessments more objective, using South Africa as a test case.
Using nonparametric niche‐based modelling (generalized additive model; GAM) calibrated on the current distribution of each South African biome, we mapped regions of the world that are climatically similar to South African biomes. Lists were produced of countries with the largest areas climatically similar to South Africa overall, and to each biome separately. Validation of the usefulness of the approach was sought by evaluating whether the main invasive plant species in South African biomes occur naturally, or have adventive ranges, in regions mapped as analogous to South African biomes.
A very large part of the world is climatically similar to South Africa, with eight countries having larger areas of land classified as climatically similar to South African biomes than the total area of South Africa. Almost all the most prominent invasive species in South African biomes occur naturally or are invasive outside their natural range in areas with similar climates to those that occur in parts of South Africa. This confirms the value of objective climate matching in screening protocols.
We examined climatic conditions for a representative sample of major invasive plants from other parts of the world. The analysis identified several species that are already invasive in regions that have matched climates in South Africa but that are not yet introduced or, if already present, have not yet invaded large areas. For example, the following known invasive species should be considered high‐risk species in South African grasslands: Alliaria petiolata , Cytisus scoparius , Gleditsia triacanthos , Heracleum mantegazzianum , Hieracium pilosella , Juniperus communis , Pinus contorta , P. monticola , P. ponderosa , P. sylvestris , Prunus laurcerasus , and P. serotina . Objectively matched climatic regions are also useful as a first‐cut assessment when evaluating species with no invasive history.
... Arguably, the most limiting criterion of warning lists is their reliance on invasion history-whether a given species has a history of invasion elsewhere (Figure 1a; Bomford et al., 2005;Faulkner et al., 2014;Hulme & Firn, 2015;Kulhanek et al., 2011;Ricciardi, 2003;Richardson & Thuiller, 2007). The use of invasion history arises from a deceptively simple premise: species that have a history of invasion possess intrinsic and/or inherent attributes that may also allow them to become invasive elsewhere (hereafter 'invasion syndromes'; Hayes & Barry, 2007;Novoa et al., 2020). ...
... The use of invasion history arises from a deceptively simple premise: species that have a history of invasion possess intrinsic and/or inherent attributes that may also allow them to become invasive elsewhere (hereafter 'invasion syndromes'; Hayes & Barry, 2007;Novoa et al., 2020). But the logical flaw in using this criterion is that many species, despite having some or all attributes consistent with invasion syndromes, are yet to be transported, introduced, and/or establish alien populations beyond their native ranges and, therefore, have no invasion history (hereafter 'potential invaders'; Figure 1b; Bomford et al., 2005;Kulhanek et al., 2011;Ricciardi, 2003;Richardson & Thuiller, 2007;Seebens et al., 2021). Given the escalating rate of new biological invaders and invasions (Fenn-Moltu, Ollier, Bates, et al., 2023a;Fenn-Moltu, Ollier, Caton, et al., 2023b;Pili et al., 2023 In this study, we advance quantitative invasion risk assessment tools to allow invasion biologists and biosecurity authorities to identify invasion syndromes and forecast potential invaders. ...
The ever‐increasing and expanding globalisation of trade and transport underpins the escalating global problem of biological invasions. Developing biosecurity infrastructures is crucial to anticipate and prevent the transport and introduction of invasive alien species. Still, robust and defensible forecasts of potential invaders are rare, especially for species without known invasion history. Here, we aim to support decision‐making by developing a quantitative invasion risk assessment tool based on invasion syndromes (i.e., generalising typical attributes of invasive alien species). We implemented a workflow based on ‘Multiple Imputation with Chain Equation’ to estimate invasion syndromes from imputed datasets of species' life‐history and ecological traits and macroecological patterns. Importantly, our models disentangle the factors explaining (i) transport and introduction and (ii) establishment. We showcase our tool by modelling the invasion syndromes of 466 amphibians and reptile species with invasion history. Then, we project these models to amphibians and reptiles worldwide (16,236 species [c.76% global coverage]) to identify species with a risk of being unintentionally transported and introduced, and risk of establishing alien populations. Our invasion syndrome models showed high predictive accuracy with a good balance between specificity and generality. Unintentionally transported and introduced species tend to be common and thrive well in human‐disturbed habitats. In contrast, those with established alien populations tend to be large‐sized, are habitat generalists, thrive well in human‐disturbed habitats, and have large native geographic ranges. We forecast that 160 amphibians and reptiles without known invasion history could be unintentionally transported and introduced in the future. Among them, 57 species have a high risk of establishing alien populations. Our reliable, reproducible, transferable, statistically robust and scientifically defensible quantitative invasion risk assessment tool is a significant new addition to the suite of decision‐support tools needed for developing a future‐proof preventative biosecurity globally.
... In addition, cacti species generally have high tolerance to extreme conditions and prolific reproduction rates (Walters et al., 2011). Consequently, this, in combination with the high diversity of local environmental conditions (Richardson and Thuiller, 2007), has led to most cacti species forming large, dense infestations that reduce the quality of grazing land in South Africa (Du Toit, 1942;Dean and Milton, 2000;Walters et al., 2011). Evidently, more than 900 000 ha in South Africa were abandoned by landowners in the 1940s owing to the invasion of Sweet prickly pear Opuntia ficus-indica (Du Toit, 1942;Dean and Milton, 2000). ...
... This observation contradicts the popular notion that many cacti species could decline because of adverse future climate impacts in their native rangethe Americas (Larios et al., 2020;Pillet et al., 2022) although Larios et al. (2020) found that the populations of the threatened and declining acuña cactus would remain stable under 2080 climate projections. It is possible that the myriad of environmental conditions and the associated biomes in South Africa create refugia for many alien and invasive species, including the cacti species as previously demonstrated (Richardson and Thuiller, 2007). Our findings complement the report by Masocha and Dube (2018), who showed that global terrestrial habitats, including southern Africa, are susceptible to cacti invasions under climate change. ...
Tephrocactus articulatus (Pfeiff.) Backeb (family: Cactaceae) is an emerging invader plant that is native to Argentina and was introduced as an ornamental plant in South Africa. The South African national regulations and legislation for controlling biological invasions dictate that emerging alien species must be eradicated. We evaluated the effectiveness of foliar spray in clearing the populations of T. articulatus, and determined the management challenges in 16 representative sites. We also applied bioclimatic models to forecast how T. articulatus invasion might respond to climate change. The exposure to climate change forecasts for T. articulatus was quantified using the Intergovernmental Panel on Climate Change-IPCC (2014) two representative concentration pathways-RCP scenarios (4.5 and 8.5) for the 2061-2080 period. Overall, the foliar spray method significantly suppressed T. articulatus populations in all sites (i.e., 75-99%) except in four sites that did not display the population suppression threshold of X ≥ 75%. The clearing success (i.e., % of dead plants), was significantly and negatively correlated to the size of the site (ha) wherein the bigger sites had relatively low success. Climate suitability projections under the RCP4.5 and RCP8.5 scenarios for T. articulatus produced excellent data fits (i.e., training AUC = 0.939 and test AUC = 0.914). Noteworthy, both future scenarios model projections have shown an expansion of suitable habitat for T. articulatus: 49.9% and 60.4% respectively, of the current estimated total spatial coverage of 219102 km 2 , and with possible expansion into neighbouring countries, Namibia and Botswana. The significant variation in the projections was contributed by precipitation in the wettest (47.5%) and warmest quarters (48.9%). Our results advance the importance of predictive models in planning optimisation in the management of emerging alien plant species in South Africa: if the ongoing eradication of T. articulatus in the core invasion areas fails, and climate change prevails, a switch from foliar spray to biological control method will be essential.
... Regenerating status was considered "good" when seedling density > sapling/coppicing density > adult tree density, "fair" when seedling density > sapling /coppicing density = adult density, "poor", when the species survived in only the sapling/ coppicing stage but not in the seedling stage, "none", for species with no sapling / coppicing or seedling stages but present as adult trees, and "new" when adults of a species were absent but sapling / coppicing and/or seedling stage(s) were present (Sukumar et al., 1992) 2.2.3. Data analysis Data analysis of the regenerating recruits was based on standard phytosociological indices involving: frequency of distribution, abundance, and density of the representative recruits of the study site (Supriya and Yadava, 2006;Shukla, 2009amd Chikkahuchaiah et al., 2016; diversity index in richness among species (Shannon-Wiener,1963); The degree of evenness or equitability (Pielou, 1969); species in semi-quantitative scale (Pryor, 1981); relative density, relative abundance and relative frequency (Misra, 1968); Importance Value Index (IVI) (Shukla and Chandel, 1980); distribution patterns with the "Rule of Thumb" designated as; Regular (< 0.03), Random (0.03 -0.05) and Contiguous (> 0.05) distribution (Curtis and Cottam, 1956) and Life form spectrum (Raunkiaer, 1934). ...
... Species diversity is one of the major criteria in recognizing the importance of an area for conservation, hence an index associated with some level of variations in terms of richness and evenness (Edwin-Wosu and Edu, 2013). Species diversity could be low due to disturbance but an increased interval between disturbances also increases diversity (Kalacska et al., 2004), and also can allow community succession to progress beyond a typical stage, causing changes in plant community structure (Richardson and Thuiller, 2007;Edwin-Wosu and Anaele, 2018).A greater contiguous distribution pattern among the regenerating species of herbaceous and shrubby life forms occurred. However, a least random and least regular pattern of distribution within HG and Sh recruits where respectively reported. ...
This study assessed the floristic composition, structural classification and phytosociology of life form regeneration, mode of regeneration and demographic status of regeneration in vegetation forest, 4 years after pollution impact. It was aimed at evaluating the phytoremediation potential of some hydrocarbon tolerant macrophytes (HTM). Conventional ecological approach involving stratified simple random design method and phytosociological indices were used. Result has classified the study site flora as low land secondary mosaic vegetation with heterogenous continuum in spatial and closed horizontal structural arrangement. Phytosociological dynamics of 51 herbaceous and 12 shrubby life forms of 63 representative species under 21 families and 49 genera of angiosperms recorded changes. Four prevalently dominant families very abundant with highest species diversity richness and three families in abundance were recorded. Shrubby recruit was lower than Herbaceous recruits with the Herbaceous sedge (HS) recording highest recruits among regenerating life forms (HS>HG>HH>HCl). The herbaceous life form had Chamaephytes 33(64.71%) and Hemicryptophytes 18(35.29%). The shrubby life form recorded 2(11.11%) Nanophanerophytes and Mesophanerophytes respectively and 8(66.67%) Microphanerophytes. The herbaceous life form mode of regeneration had 28 recruits with multiplier mode, and 23 recruits with single mode of regeneration. Four recruits exhibited multiplier mode and eight with single mode of regeneration across shrubby life form. Demographic status of regeneration revealed greater seedling than sapling density devoid of adult tree recruits, thus implies "successful and new regeneration"
... Plant species can naturalise or invade in novel biomes not occupied in the native range (Gallagher et al. 2010;Richardson & Thuiller 2007). Some studies suggest that eucalypts with wider environmental tolerance are more likely to be planted outside the native range (introduction) and to reproduce successfully (naturalisation and invasion). ...
... The risk of eucalypt invasion varies along time and space. Species and plantations that today seem harmless may require attention in the future (Richardson & Thuiller 2007). ...
Eucalypt plantations expanded across many countries and became subject to
controversy, particularly about their ecological impacts and invasive potential. The same is true in the Iberian Peninsula (Iberia) regarding Eucalyptus globulus Labill. This thesis is
composed by six studies (chapters) tackling poorly explored aspects in these domains, with the following objectives:
a) to evaluate potential future dynamics of E. globulus plantations in Iberia according to different climate change scenarios and possible conflicts with high biodiversity areas (Chapter 1);
b) to explore the influence of different factors on the natural establishment of E. globulus (Chapters 2-5); c) to perform a review of the literature investigating the natural establishment of eucalypt species (Chapter 6).
In Iberia, under both climatic scenarios, the suitable range of E. globulus plantations is
expected to shrink and conflicts with high biodiversity areas may aggravate (Chapter 1). A
countrywide survey in Portugal to estimate E. globulus recruitment, using Google Street
View, showed that recruitment is mostly influenced by climatic variables (annual precipitation and thermal amplitude) and that Google Street View is a cost-efficient alternative to car surveys (Chapter 2). Field surveys in E. globulus plantations in Central Portugal showed abundant recruitment along plantation edges, influenced by local factors such as soil cover and tree age. Wildlings, mostly adult, are spread up to 76 meters from plantations (Chapter 3). A sowing experiment using E. globulus seeds showed that germination and survival was enhanced after harrowing (Chapter 4). A seed predation experiment revealed that E. globulus seeds are highly attractive but they have escaped in many locations (Chapter 5).
The literature review retrieved 37 studies, addressing 61 eucalypt species in seven
countries. Key factors influencing eucalypt recruitment include fire, propagule pressure and disturbances (Chapter 6).
... In order to prevent Brazil from having similar losses, preventive and control measures should be adopted, especially in the vicinity of the introduction areas (Richardson and Thuiller 2007). One trend observed in the study of the invasion process is that disturbed environments tend to be more susceptible to invasion (Pysek and Richardson 2007). ...
... This type of material is still scarce and not detailed. However, considering that invasion control is much more expensive in comparison to prevention (Thuiller et al. 2005, Richardson and Thuiller 2007, Broennimann and Guisan 2008 and that the invasion process in Brazil is already under way , it is necessary that these control measures be systematized with urgency, based on the information available in Brazil and the world. ...
Tropical forest plantations in monoculture are simple ecosystems much less complex than natural tropical forests with hundreds of tree species. The simplification allows concentrating the site resources for genetic material of interest reducing silvicultural treatments. Such forests occupy approximately 9.8 million ha in Brazil and 96% are composed of Eucalyptus or Pinus. Recently, governmental and civil society actions aimed at increasing forest cover in at least 12 million ha of degraded areas in Brazil. In addition, estimates indicate about 40 million ha of degraded grasslands. The expansion of forest cover in these areas with monospecific forest plantations of non-N2-fixing species requires fertilizer inputs and may have limited productivity, although several species are promising in the composition of these more biodiverse forests that can be used for different purposes, such as timber products, soil protection in sloping areas, and recovery of degraded soils. Most significant benefits in terms of productivity and ecosystem services have been obtained, when mixtures involve nitrogen N2-fixing trees and non-N2-fixing trees. In this chapter benefits of mixed plantings are introduced, as well as a brief history of these plantations in Brazil and the main combinations tested in Brazil and the other potentials.
... In order to prevent Brazil from having similar losses, preventive and control measures should be adopted, especially in the vicinity of the introduction areas (Richardson and Thuiller 2007). One trend observed in the study of the invasion process is that disturbed environments tend to be more susceptible to invasion (Pysek and Richardson 2007). ...
... This type of material is still scarce and not detailed. However, considering that invasion control is much more expensive in comparison to prevention (Thuiller et al. 2005, Richardson and Thuiller 2007, Broennimann and Guisan 2008 and that the invasion process in Brazil is already under way , it is necessary that these control measures be systematized with urgency, based on the information available in Brazil and the world. ...
The soil harbors an incredibly high biodiversity, composed by many macro- and microorganisms, where bacteria are the most abundant and diverse ones. These tiny organisms are major players in nutrient cycling and are responsible for the maintenance of soil fertility and plant productivity by direct and indirect interactions. They are able to biologically fix nitrogen, produce phytohormones, increase nutrient bioavailability, protect from pathogens, and modulate plant responses to stress among many other functions. However, they are structured in very complex communities and controlled by many different factors and their responses to land use and management in forestry systems are still in the very beginning of our understanding. In this chapter, we present briefly the role of the bacterial community in forestry ecosystems, and how it responds to intercropping of Eucalyptus and Acacia. We show that there is a strong indication that the consortium of Eucalyptus with legume trees can integrate the soil bacterial community, increasing microbial activity and system stability with direct benefits to soil biogeochemistry. We also show that the bacterial biodiversity associated with trees can be explored in a biotechnological way, representing a green technology to optimize plant growth improving the sustainability of wood production.
... In order to prevent Brazil from having similar losses, preventive and control measures should be adopted, especially in the vicinity of the introduction areas (Richardson and Thuiller 2007). One trend observed in the study of the invasion process is that disturbed environments tend to be more susceptible to invasion (Pysek and Richardson 2007). ...
... This type of material is still scarce and not detailed. However, considering that invasion control is much more expensive in comparison to prevention (Thuiller et al. 2005, Richardson and Thuiller 2007, Broennimann and Guisan 2008 and that the invasion process in Brazil is already under way , it is necessary that these control measures be systematized with urgency, based on the information available in Brazil and the world. ...
Nitrogen (N) supply is one of the key factors for the success of forest plantations and the search for strategies that allow constant N inputs with reasonable cost is desirable. The ability to fix and accumulate large amounts of N confers adaptive characteristics to the legumes that excel over other species. Here we address the biological nitrogen fixation (BNF) as an ecological strategy in mixed-forest plantations, allowing N fixation to act positively on the development of non-N2-fixing species. We include a brief description on the BNF establishment and the taxonomy and efficiency of the relevant bacteria. In Brazil, the contribution of BNF in mixed-forest plantations, mainly the ones between Eucalyptus spp. and Acacia spp., has demonstrated that their use is improving the quality of the soil organic matter and the N status of the system. The productivity of the non-N2-fixing species increases, especially in oligotrophic soils, varying from 2 to 90%. Normally, the BNF contribution is higher in mixed plantations than in monocultures and the amount of biologically fixed N makes up 50–60 kg ha⁻¹ year⁻¹. The studies on nitrogen-fixing tree species and mixed-species stands recently were intensified. However, large-scale use of mixed forest plantations is still challenging.
... In order to prevent Brazil from having similar losses, preventive and control measures should be adopted, especially in the vicinity of the introduction areas (Richardson and Thuiller 2007). One trend observed in the study of the invasion process is that disturbed environments tend to be more susceptible to invasion (Pysek and Richardson 2007). ...
... This type of material is still scarce and not detailed. However, considering that invasion control is much more expensive in comparison to prevention (Thuiller et al. 2005, Richardson and Thuiller 2007, Broennimann and Guisan 2008 and that the invasion process in Brazil is already under way (Aguiar Jr et al. 2014), it is necessary that these control measures be systematized with urgency, based on the information available in Brazil and the world. ...
The use of exotic species by man can generate diverse environmental and economic benefits. Nevertheless, when dealing with exotic species, it is necessary to take into account its complex relationship with human communities and natural ecosystems. As a backfire, exotic species can alter the properties of local ecosystems, causing economic and environmental damage if they become invasive (Richardson et al. Divers Distrib, 17: 771–787, 2011a; Richardson et al. A compendium of essential concepts and terminology in invasion ecology. In: Richardson, D.M. (ed.) Fifty years of invasion ecology: the legacy of Charles Elton. Blackwell: Oxford, pp 409–420, 456, 2011b). In addition to the effect on the ecological integrity of ecosystems and, consequently, on the services provided by them, exotic species can be the cause of great economic losses directly influencing agriculture, forestry, and public health (Pimentel et al. Agric Ecosyst Environ, 84: 1–20, 2001). Recently, Vitousek et al. (2017) proposed that biological invasions are so widespread and the impacts are so vast that this should be considered as a significant component of global environmental change.
... 6 . Given this diversity, it is unsurprising that large areas of the planet have climatic and environmental analogues to South Africa ( Fig. 1.3; see also Richardson and Thuiller 2007). ...
... Here the global extent of these seven biomes is shown to emphasise how much of the world is represented in South Africa, giving rise to the expression "a world in one country". Note a separate analysis has also shown that a significant proportion of the world has a climate similar to South Africa (Richardson and Thuiller 2007). ...
South Africa has much to offer as a location for the study of biological invasions. It is an ecologically diverse country comprised of nine distinct terrestrial biomes, four recognised marine ecoregions, and two sub-Antarctic Islands. The country has a rich and chequered socio-political history, and a similarly varied history of species introductions. There has been a long tradition of large-scale conservation in the country, and efforts to manage and regulate invasions began in the nineteenth century, with some notable successes, but many setbacks. With the advent of democracy in the early 1990s, South Africa established large alien species control programmes to meet the dual demands of poverty alleviation and conservation, and has since pioneered regulatory approaches to address invasions. In terms of research, South Africa has played an important role in the development of invasion science globally. It continues to have one of the most active communities anywhere in the world, with strengths in theoretical and applied invasion science, and world-leading expertise in specific sub-disciplines (e.g. the classical biological control of invasive plants).
... Predictive models for the assessment of land use change play an important role in the field of biogeography (Guisan and Zimmermann 2000;Scott 2002;Guisan and Thuiller 2005) and conservation planning (Burgman et al. 2005; Barry and Elith 2006;Elith and Leathwick 2007;Richardson and Thuiller 2007;Rodríguez et al. 2007). These models draw on the data produced by remote sensing, Geographical Information Systems (GIS) and new statistical methods (Guisan and Zimmermann 2000;Ferrier et al. 2002). ...
... There are forests on the Saharan Atlas Mountains with above all Pinus halepensis (Aleppo pine) and scrub vegetation, mainly Juniperus phoenicea and Juniperus oxycedrus (prickly juniper). The most common form of agriculture is cereal farming (Pouget 1980). Zahrez El Gharbi is made up of four communes, Djelfa (capital of the wilaya or province), Zaafrane, Ain Maabed, and Charef, and has a population of 345,255 inhabitants according to the National Census of 2008. ...
Modeling techniques have the power to predict land use change. Our research had three main aims: firstly, to compare and contrast the predictive performance of individual models versus consensus methods; secondly, to compare the different consensus methods; and finally, to compare their predictive performance for generalized and marginal land uses in the environment in the study area. Seven individual models were used to generate the suitability maps for each type of land use in Zahrez El Gharbi (Algeria), characterized by the suitability values for their occurrence. Seven consensus methods were created by combining the individual models. The predictive performance of the individual models and of the consensus methods was assessed by calculating the area under the curve (AUC). For each type of land use, the predictive quality of the consensus methods was considerably better than that of the individual models. The weighted averages method (WA) proved the most efficient of the seven consensus methods. The types of land use have a significant influence on the predictive quality, in that the AUC values increase in line with increases in the marginality of the particular type of land use. The improvements in predictive quality achieved by consensus methods in general and the weighted averages method (WA) in particular would substantially resolve the different sources of uncertainties resulting from the use of individual models and from the environmental characteristics of the different types of land use.
... The climate matching hypothesis suggests that invasive alien species are more likely to establish in areas with climates similar to their native environmental ranges [103,104]. According to their original geographic range, P. ovalis occurs in drier areas of Africa, Asia, Comoros, Madagascar, and in tropical biomes , so more arid and less climatically and topographically variable islands like Lanzarote and Fuerteventura, as well as the south of Tenerife and Gran Canaria, could present environmental favorability for the species. ...
Invasive species represent a significant threat to biodiversity and ecosystem conservation, with their impacts often amplified in island ecosystems. Species distribution models (SDMs) can infer the potential habitat throughout the life of an organism and are considered a valuable tool for predicting the risk of expansion of invasive plants and animals. In our approach, we used an ensemble of four presence–absence models (GLM, GAM, Random Forest, and BART) calibrated only with data collected in Tenerife, the island with the best representation of the species, to infer the habitat suitability for Pluchea ovalis (Pers.) DC. (Asteraceae). Subsequently, we transferred the ensembled model to the rest of the Canarian Island archipelago. Our results show that under near-present conditions, the suitable areas are in the coastal and mid-elevations of the south slope sectors of Tenerife and Gran Canarian Islands, as well as a vast portion of the westernmost and drier islands, always coinciding with ravines and highly disturbed ecosystems. In addition, we forecasted the potential distribution of Pluchea ovalis under different climate change conditions (SSP126, SSP370, and SSP585), showing how its habitability would increase in the worst scenarios. Both contexts favor areas gained by the species in places where they are currently not present, revealing new suitable sectors in the westernmost islands.
... Many of these species are known to be invasive elsewhere. For example, only in Brazil (which has large areas that are climatically similar to South Africa; Richardson and Thuiller, 2007), the following six palm species that are planted in South Africa are invasive: Archontophoenix cunninghamiana, Caryota urens, Elaeis guineensis, Livistona chinensis, Phoenix roebelenii, and Roystonea oleracea (Instituto H orus, 2024). ...
Trees have a multifaceted influence on ecosystems globally. Treescapes have been manipulated by humans over millennia for ecological, economic, and cultural reasons that have changed over time and continue to change. In South Africa tree planting over three centuries has radically affected the composition of tree-scapes, contributing important ecosystem services, but also disservices. Rapid global change calls for diverse interventions to create more resilient ecosystems. Many nature-based solutions involve manipulating tree cover in rural and urban landscapes. There is a need for a spatially-explicit database of planted trees in South Africa to serve as the foundation for policy and management decisions. We used the community science platform iNaturalist to create a comprehensive database of planted trees in South Africa. Records were carefully checked to verify the accuracy of taxon identifications, locality data, and categorization as planted rather than wild-growing trees. The cleaned database contained 35,303 records of 805 planted tree taxa; over 90 % of records were identified to species level. Almost a third of taxa (32.2 %) belong to three families: Fabaceae (97 taxa), Myrtaceae (80 taxa) and Arecaceae (78 taxa). Rarefaction and extrapolation curves suggest fairly comprehensive sampling, but several regions are under-sampled. Non-native taxa dominate, with Melaleuca viminalis having the most records. The Western Cape has the highest number of records and taxa, particularly in urban areas. Both native and non-native trees provide key ecosystem services, but non-natives dominate. The database provides the first spatially-explicit open-access resource for guiding decisions on tree planting and the management of planted trees in South Africa. It offers a snapshot of tree planting trends, predominantly from recent years, leading to some underrepresentation of historically planted species. The database has numerous potential uses, including guiding management of trees pests and diseases, urban greening initiatives , monitoring for new invasions, and planning nature-based solutions.
... Climate matching is a tool commonly used to assess how climatic conditions of a recipient region (i.e. an invaded region) will affect the survival of potential invasive species Mandrak & Cudmore, 2015). Climate matching involves quantifying the similarity in climates between a species' source location, that is, native and introduced ranges, using a suite of bioclimatic variables, such as mean annual temperature, and has been validated for predicting invasive species survival in introduced regions (Bomford et al., 2009(Bomford et al., , 2010Bradie et al., 2015;Duncan et al., 2001;Forsyth et al., 2004;Howeth et al., 2016;Van Wilgen et al., 2009) and serves as a useful method for invasive species screening protocols (Richardson & Thuiller, 2007). Predictions based on climate matching will likely be disrupted by climate change due to disproportional changes in climates among ecoregions (Chapman et al., 2017), implying that climate change projections should be incorporated into analyses of biological invasions at regional scales (Britton et al., 2010;Campbell et al., 2022;Hubbard et al., 2023;Kriticos, 2012). ...
Aim
We assess climate similarity among global freshwater and terrestrial ecoregions under historical and future climate scenarios to determine where climate change will impact the climate filter of invasion process.
Location
Global.
Methods
We used the Climatch algorithm to conduct a climate‐match analysis to quantify the climate similarity between freshwater and terrestrial ecoregions of the world. Climate match was modelled between all freshwater and terrestrial ecoregions. The analysis was conducted under historical climates and projected climates of 2081–2100 (2090) under three shared socioeconomic pathways SSP2‐4.5, SSP3‐7.0, SSP5‐8.5. Climate matches of each ecoregion were presented as mean climate match to all other ecoregions of the same set. Friedman's non‐parametric rank sum two‐way analysis of variance with repeated measures was used to examine differences in mean climate match between climate scenarios.
Results
Mean climate match of ecoregions was projected to increase significantly with small effect sizes for freshwater ecoregions (recipients: 0.132; sources: 0.105), and moderate and small effect sizes for terrestrial ecoregions (recipients: 0.330; sources: 0.259). Climate change was predicted to increase mean climate match in North America and Eurasia, particularly in the Arctic by 2090 under each SSP. Ecoregions in central Africa and South America were predicted to have reduced mean climate match. Ecoregions within larger countries (e.g. Australia, Canada, USA) showed variation in mean climate match.
Main Conclusion
Climate change projections of bioclimatic predictors of species invasions were shown to increase in homogeneity under higher emissions scenarios. Furthermore, we demonstrate how climate change will provide opportunities for invasive species transported among ecoregions to survive under new conditions and identify where the climate filter of the invasion process will be most affected. Findings can be used to inform conservation actions for mitigating the impacts of introduced species by identifying potential risky source regions of future freshwater and terrestrial invasions under climate change.
... Riparian systems are highly threatened by various factors that modify their water regime, such as canalization, dredging, dam construction, irrigation systems and water extraction (EEM 2005). In a context of global change, biological invasions are added as another of its main threats (Richardson et al. 2007), being in turn facilitated by the alteration of ecosystems (Moreno et al. 2015). Poff et al. (2011) reported that the most successful invasive processes in riparian systems develop in areas where the hydrological regime has been previously modi ed. ...
Riparian systems are highly threatened by alterations in its hydrological regimen and biological invasions. To guide its conservation is important to understand the relationships established between biological invasions and abiotic conditions affected by the hydrological regimen. We analyze the relationship between the distribution pattern of soil sand content and the invasive process of the woody invasive Gleditsia triacanthos in riparian forests of the Esteros de Farrapos and Islands of Uruguay River National Park, zoning the study area according to the type of relationship between both variables. We integrate the use of regression trees and geographic information systems to zone this relationship. This is a novel approach to study the relationships between an invasive species and its environment. Areas with lower sand content were found to be favorable for the development of the invasive species, and areas with higher sand content were found to limit its spread. No relationship was found between the intermediate sand content and the progress of the invasive process. This work highlights the complexity inherent to the definition of causal relationships in highly heterogeneous systems such as riparian ecosystems. Spatial analysis techniques are a useful tool for this approach.
... Gleditsia triacanthos es una especie leñosa perteneciente a la familia de las fabáceas originaria Norte América (USDA, 2017). En la actualidad se la considera como invasora en el cono sur (Chaneton et al., 2004;Nebel and Porcile, 2006) y como potencial invasor en Australia (Csurhes and Kriticos, 1994) y Africa (Richardson and Thuiller, 2007). Tolera un amplio rango de condiciones ambientales (USDA, 2017). ...
Los ecosistemas fluviales presentan alta vulnerabilidad. Su degradación se asocia fundamentalmente a alteraciones del régimen hídrico afectando la deposición y consecuentemente las condiciones edáficas determinantes del establecimiento de la vegetación pudiendo afectar procesos invasivos de especies vegetales reconocidos como otra importante amenaza. Por tanto, resulta relevante comprender la relación entre las condiciones edáficas y los procesos invasivos. Este trabajo evalúa la relación entre el contenido de arena y la distribución de la leñosa invasora Gleditsia triacanthos en un bosque del Río Uruguay. Se caracterizó el patrón espacial de la variación en la textura del suelo, el patrón de distribución de G.triacanthos y las relaciones existentes entre éste y el contenido de arena del suelo. Se detectó variación en la textura del suelo en el eje norte-sur y en el eje este-oeste. Se detectó una relación compleja entre la abundancia de G.triacanthos y el contenido de arena del suelo.
... TDM, tür gereksinimlerini vurgulayan niş kavramına, özellikle (ancak bununla sınırlı olmamak üzere) tür dağılımlarını kontrol eden abiyotik faktörlerin temsillerine dayanmaktadır (Franklin, 2010 (Ferrier, 2002), etki değerlendirmesi ve kaynak yönetiminde (López-López vd., 2007), ekolojik restorasyon ve ekolojik modellemede (Akçakaya, 2001;Martínez-Meyer vd., 2004), istilacı tür yönetimi (Richardson ve Thuiller, 2007) ve küresel çevresel değişimin türler ve ekosistemler üzerindeki etkilerinin tahmin edilmesinde (Akçakaya vd. 2006) uygulanmıştır. ...
In this study, habitat suitability for the Saffron milk-cap mushroom (Lactarius deliciosus) was investigated through GIS-integrated statistical and machine-learning methods in the Refahiye and Tekçam planning units. For this purpose, the relationships between predictive variables at different scales, such as topography, stand structure, and climate, and the presence/absence of the species were analyzed. 173 temporary sampling plots in temperate coniferous forests were determined by a simple random sampling method. Empirical relationships between the presence of the relevant species and environmental factors were defined using species distribution models. The model success was evaluated according to the TSS (True Skill Statistics) and ROC curve (Receiver Operating Characteristic curve). The modeling results indicated that the machine learning models performed slightly better than the statistical ones, however, all the models obtained total accuracy values greater than 80%. The random forests (RF) model was the most sensitive and specific with the highest values of ROC (0.96) and TSS (0.91), thus identifying it as the best modeling method. According to the results, L. deliciosus is a species highly affected by interannual variations in temperature, precipitation, solar radiation, and stand variables such as canopy closure. Furthermore, these methods can be valuable tools for predicting the distribution of other NWFPs and serve as a basis for elaborating sustainable management plans.
... Today it is categorized as invasive in Oceania, Europe, and many South American countries, such as Uruguay and Argentina. In Australia [7] and Africa [8], it is a potentially invasive species. ...
In Uruguay and neighbouring countries, Gleditsia triacanthos is an exotic tree species categorized as invasive; it produces severe ecological impact as it displaces native species, changing the structure of the native forest community. One way to mitigate its negative impact is to identify opportunities to use it by revaluating its biological products. This work studies the applicability of this species as a source of both combustible and non-wood products. The heat capacity, chemical composition, and anatomical description of its wood was determined. Polyphenols extracted by way of an adhesive for timber products were finally added, partially substituting petroleum derivatives; it showed promising results.
... Consequently, different underlying mechanisms of biological invasion have been proposed (Catford et al., 2009;Di Castri, 1989;Theoharides & Dukes, 2007). Among them, the 'climate matching' hypothesis (Richardson & Thuiller, 2007;Thuiller et al., 2005), which postulates that alien species are most likely to establish in areas that are climatically similar to their native range, has received mounting evidence (e.g., Cao Pinna et al., 2021;Capinha et al., 2015;Monnet et al., 2020). Recently, Yang et al. (2021) showed that the level of floristic homogenization due to plant introductions increases with climatic similarity, even among geographically distant regions. ...
Aim
Understanding the historical and contemporaneous drivers of invasion success in island systems can decisively contribute to identifying sources and pathways that are more likely to give rise to new invaders. Based on a floristic‐driven approach, we aimed at determining the origins of the invasive alien flora of the Canary Islands and shedding light in the mechanisms shaping their distribution within the archipelago.
Location
Canary Islands.
Taxon
Vascular plants.
Methods
An updated checklist of the invasive alien flora of the Canary Islands was assembled along with complementary information related to the native biogeographical regions, stage of invasiveness and dates of naturalization. Statistical models were employed to describe differences in the number of species over space and time. We also used multivariate techniques to evaluate competing hypotheses related to the mechanisms driving invasive floristic composition within the archipelago.
Results
We provided a list of 149 alien plant species with a certain degree of invasiveness. The greatest number of invasive species originated from the Neotropics followed by the Cape Region, tropical Africa and the Mediterranean Basin. We observed a slow but steady increase in numbers of invasive species until the 1950s, followed by a stronger rise thereafter. In order to explain composition dissimilarity of the invasive flora among islands, a climatic matching hypothesis was fully supported, with geographic isolation and contemporary human‐mediated connectivity hypotheses receiving less and null support respectively.
Main Conclusions
We showed that the Neotropical region is the main source of plant invasions to the Canary Islands, outnumbering those from other regions with a Mediterranean‐type bioclimate. The assembly of the invasive flora within the archipelago appears to be driven primarily by climate, but with geographic distance also playing a role. This study calls for archipelago‐dependent assessments of the underlying mechanisms that contribute to plant invasion success within insular systems.
... The best way to combat an invasive species is prevention (Richardson and Thuiller 2007). Once established, eradicating an invasive species is extremely difficult or impossible (Koch et al. 2006). ...
The genus Baccharis (Asteraceae) comprises over 440 species distributed along North and South America. Some species of this genus have remarkable invasiveness, and one of these species is the South American shrub Baccharis dracunculifolia DC. Most of the introductions of non-indigenous species are held indirectly through trade, so it is believed that this species could become invasive worldwide with a particular interest in the North American continent because of the increasing sale of products derived from honey to this continent. The resin extracted from B. dracunculifolia is the leading source for preparing the green propolis produced in Southeastern Brazil. Thus, the main objective of this work is to apply an approach based on distribution modeling to investigate possible areas of high environmental suitability for B. dracunculifolia in the North American continent and the potential to the entire globe using current and two future scenaries. Our results show many areas of environmental suitability for B. dracunculifolia. This species can invade over 33 countries distributed into five continents, including North America, some of the most critical parts of the southern USA, and large areas in Mexico. Since the best way of countering biological invasions is prevention, we propose that the introduction of this species should be monitored.
... Caucasian hogweeds have been analyzed on various scales (regional, landscape, national, continental) and have been considered a plant invasion of at least continental range [65][66][67]. It was predicted that the spread of invasive hogweeds might lead to the colonization of other continents [68]. Some studies concerned the rules of plant dispersal and the definition of vectors of this process, including anthropogenic impacts [69][70][71][72]. ...
Caucasian hogweeds are plants introduced to Europe from the Caucasus area. This review concerns the two most common ones—the giant hogweed Heracleum mantegazzianum and the Sosnowsky’s hogweed Heracleum sosnowskyi. The first of them was imported as garden decorations from the 19th century, mainly to Western Europe, while the second one was introduced from the mid–20th century to agricultural areas in Eastern Europe. Nowadays, these two species create one of the most problematic invasions in the world. This review aimed to synthesize research on those invaders based on 277 articles selected from the “Scopus” database. Most of the articles concerned their extensive distribution, at least on a continental scale and the rapid dispersal. The reviewed research showed that the complex physicochemical properties of hogweeds tissues and secretions significantly affected insects, aphids, ants, nematodes, fungi, soil microorganisms, plant communities, birds, and many other components of the ecosystems. This knowledge turned out to be disproportionately small to the scale of the problem. The review also showed what ecological traits of hogweeds were responsible for their wide and various role in the environment. Thus far, no effective method to eradicate Caucasian hogweeds has been found. This could be a growing mistake, given that they are probably during the rapid evolutionary changes within the range of their invasion.
... In Romania, it is primarily naturalized in riverine environments and urban localities (Doroftei et al. 2009), whereas in South Africa, it occurs in savannas, shrubs, xeric shrubland, and wetland areas (Henderson 2007). The honey locust is considered a potential invader of prairie biomes (Richardson and Thuiller 2007). ...
Native to the southeastern United States, the honey locust (Gleditsia triacanthos) is an invasive tree in several South American countries. Since eradication of invasive species is often costly, prevention is a better strategy. The relationship between invasive species and their habitats can be analyzed using species distribution models to produce maps of areas prone to the invasions. These maps can be used to develop efficient early detection plans of exotic species colonization. Here, we employed the Favorability Function model to assess the effects of environment and human activities on the invasive process of the honey locust in Uruguay. By integrating environmental and anthropic factors in our models, we obtained the best fitted prediction and classification indices. We showed that the southwestern region of the country concentrates the largest proportion of areas prone to the invasions. Environment was the main factor explaining the invasion of G. triacanthos, but the effect of human-related factors had a greatest effect in combination with environmental variables than on its own. We generated favorable risk maps and explanatory variables that can be used to more efficiently plan efforts to control the spread of this invasive.
... For alien species, these models can be used to extrapolate potential distribution from native ranges to other regions (transferability) . Transferability of SDMs assumes that niches are conserved in alien species (Wiens et al. 2010); consequently, predictions should properly be made only to climate analogue regions (Di Febbraro et al. 2013;Richardson and Thuiller 2007). Moreover, the size of the area predicted by SDMs can be regarded as a proxy of invasiveness, as this area represents the potential area that the species might occupy (Castro-Díez et al. 2011;Lloret et al. 2004). ...
Functional traits that predict plant invasiveness are a central issue in invasion ecology. However, in many cases they are difficult to determine, especially for a large set of species. Climatic niche traits can overcome this problem due to the ease of acquiring them for a large number of species. This effort is critical given that knowledge of species invasiveness is necessary (although not sufficient) to anticipate/manage invasive species.
In this study, we examined thermal and hydric niche traits to predict plant invasiveness. We used a set of 49 alien plant species, representative of the alien flora of Chile. Niche traits were obtained using environmental information (WorldClim) and global occurrences. Invasiveness was estimated using global niche models and projection of the potential distribution in Chile. As a final step, we reviewed the literature for a subset of species, documenting their impacts on a) biodiversity, b) crop agriculture and c) livestock.
Thermal niche breadth and thermal niche position were the most important niche traits to predict potential distribution (a proxy of invasiveness). Using thermal niche breadth and niche position traits, we constructed a graphical model that classifies alien species as highly invasive (wide thermal niche breadth and low niche position) or low potential to be invasive (narrow niche breadth and high niche position). We also found no association between our invasiveness classification and the documented impact of alien species.
... Gleditsia triacanthos es una especie leñosa perteneciente a la familia de las fabáceas originaria Norte América (USDA, 2017). En la actualidad se la considera como invasora en el cono sur (Chaneton et al., 2004;Nebel and Porcile, 2006) y como potencial invasor en Australia (Csurhes and Kriticos, 1994) y Africa (Richardson and Thuiller, 2007). Tolera un amplio rango de condiciones ambientales (USDA, 2017). ...
SOSA, B.; FERNÁNDEZ, G.; ACHKAR, M. Relación entre la propagación del proceso invasivo de gleditsia triacanthos y la deposición de arena en bosques del Río Uruguay. GeoUECE (online), v. 09, n. 16, p. 110-122, 2020.
... However, much less is known about how South Africa's native flora contributes to invasions elsewhere, by supplying naturalised and invasive species to other parts of the world. Conditions similar to those that occur in South Africa's terrestrial biomes occur over large parts of the world (Thuiller et al. 2005;Richardson and Thuiller 2007;Fig. 1.3 in van Wilgen et al. 2020, Chap. ...
... Thirdly, it could be that South African animals have few areas in the world for which they are suitable, or that they are particularly not invasive. This seems unlikely as South Africa has many areas of the world that are climate matched (Richardson and Thuiller 2007;van Wilgen et al. 2020, Chap. 1), and there are a considerable number of domestic exotic animals (see below). ...
This review provides the first assessment of animal species that are native to South Africa and invasive elsewhere in the world. While around a twelfth of all naturalised plants in the world are native to South Africa, there are very few examples of South African native marine, terrestrial, or freshwater animals becoming invasive elsewhere. We provide a narrative of each of the 34 cases that we could find. Three of these species, the Common Waxbill, Estrilda astrild, the Mozambique Tilapia, Oreochromis mossambicus and the African Clawed Frog, Xenopus laevis, were widely traded, and introduced on several continents with invasive populations becoming the subject of substantial research. Most other species are poorly documented in the literature such that it is often not known whether South African populations are the source of invasions. These species demonstrate the same trend in pathways of animals entering South Africa, moving from deliberate to accidental through time. The role of mavericks, individuals whose deliberate actions wilfully facilitate invasions, is highlighted. While South Africa has acted as an important bridgehead for the invasions of forestry pests, crayfish, fish and amphibians on the continent, it is clearly not a major donor of animal invasions, but rather a recipient. This could be due to South African ecosystems being fundamentally more invasible, or South African fauna showing reduced invasiveness, though it is likely that substantial differences in historical pathways also played a crucial role.
... However, much less is known about how South Africa's native flora contributes to invasions elsewhere, by supplying naturalised and invasive species to other parts of the world. Conditions similar to those that occur in South Africa's terrestrial biomes occur over large parts of the world (Thuiller et al. 2005;Richardson and Thuiller 2007;Fig. 1.3 in van Wilgen et al. 2020, Chap. ...
This chapter provides the first assessment of South African native vascular plants as naturalised and invasive species in other parts of the world. For naturalised species, Global Naturalized Alien Flora (GloNAF) data were used, while for invasive species an assessment was made using the peer-reviewed literature, experience of the authors, and correspondence with authorities in many parts of the world. Results show that 1093 South African native plant taxa have been recorded as naturalised, but for only 79 of these is there strong and unequivocal evidence of invasiveness in natural or semi-natural ecosystems (another 132 taxa have been listed as invasive, but do not fulfil all criteria for listing as such). Thirty-five taxa have naturalised in more than 100 regions (countries, states, provinces, districts, or individual islands), and six taxa (all grasses—family Poaceae) are naturalised in more than 200 regions. However, of these, only 12 (34.2%) are recorded as invasive, and only nine fulfil the more conservative definition of invasive. These figures indicate that to be widely distributed does not automatically translate into being a strong invader, and that taxa that are extremely successful as invaders in some regions only succeed in specific environmental and geographic settings, and many of them are not widespread alien plants. Grasses are over-represented among both naturalised and invasive South African plant exports: 15% of naturalised species and 23% of invasive species are grasses. Temperate Asia and Europe are net donors of naturalised plants to South Africa, but Australasia and the Pacific Islands have received many more naturalised plants than they have donated to South Africa. Of taxa native to South Africa recorded as unequivocally invasive outside of cultivation elsewhere, 65% occur in Australia.
... This assumes that the species' niche maintains its original features when the species reaches a new area (Peterson 2003). Under a niche conservatism approach, researchers calibrate their models using the species' native range to extrapolate the described climatic niche into new areas (Richardson & Thuiller 2007). However, risk assessment based only on the climatic niche calibrated in the native range is likely to underestimate suitable areas, as the species' observed niche may be constrained by ecological interactions (e.g. by competitors, predation, parasitism), and species may have the ability to adapt to new climatic conditions (Hof et al. 2011, Di Febbraro et al. 2013. ...
Invasive alien species are major drivers of global change that can have severe impacts on biodiversity and human well-being. Management strategies implemented to mitigate these impacts are based on a hierarchical approach, from prevention of invasion, via early warning and rapid response, to invasive species management.
We evaluated how different classes of spatially explicit models have been used as predictive tools to improve the effectiveness of management strategies. A review of literature published between 2000 and 2019 was undertaken to retrieve studies addressing alien mammal species through these models.
We collected 62 studies, dealing with 70 (26.8%) of the 261 mammal species that are considered to be introduced worldwide. Most of the studies dealt with species from the orders Rodentia (34%) and Artiodactyla and Carnivora (both 24%); the most commonly studied families were Sciuridae (13%) and Muridae (12%).
Most of the studies (73%) provided spatial predictions of potential species spread, while only ca. 15% of the studies included evaluations of management options. About 29% of the studies were considered useful in risk assessment procedures, but only because they presented climatic suitability predictions worldwide, while studies modelling suitability before a species was introduced locally are still lacking for mammals. With some exceptions, spatially explicit population models are still little used, probably because of the perceived need for detailed information on life history parameters.
Spatially explicit models have been used in relatively few studies dealing with invasive mammals, and most of them covered a restricted pool of species. Most of the studies used climate matching to evaluate the suitability of geographic areas worldwide or the possibility of species that were already established spreading further. Modelling procedures could be a useful tool to assess the risk of establishment for species not yet present in an area but likely to arrive; however, such studies are lacking for mammals.
... P r e d i c t i o n i n t h e e a r l y s t a g e s , w i t h subsequent prevention, is the most effective management strategy for invasive species, and is often the most efficient too (Richardson and Thuiller 2007). Bioclimatic envelope models are one potentially useful tool to predict climatically suitable areas for the establishment of invasive species in non-native areas (Jiménez-Valverde et al. 2011), as well as in PAs (e.g., Beaumont et al. 2009b;Vicente et al. 2013). ...
Fabiana G. Barbosa, Camila Both, and Miguel B. Araújo (2017) Invasion of protected areas by non-native species is currently one of the main threats to global biodiversity. Using an ensemble of bioclimatic envelope models we quantify the degree of exposure of South American protected areas to invasion by two invasive amphibian species. We focus on protected areas that coincide with global biodiversity hotspots. The species modeled, Lithobates catesbeianus and Xenopus laevis, have been reported to threaten local faunas in several non-native areas that they invaded, including areas in Asia, Europe, North America, and South America. We show that 87.5% of the protected areas within the Atlantic Forest may be most at risk of invasion by L. catesbeianus and X. laevis under current climate conditions, followed by areas in the Cerrado (51.7), Tropical Andes (37.6%), Tumbes-Choco-Magdalena (22.5%), and Chilean Winter Rainfall and Valdivian Forests (20.5%). Conservation plans for these regions should, therefore, consider latent threats from multiple sources including invasion by highly competitive non-native species such as the ones modeled in our study.
... Prevention is still the best way to avoid problems arising from biological invasions (Pimentel, 2002;Richardson & Thuiller, 2007;ISSAC, 2018). However, once the invasion process is recognized, control measures should be taken immediately to prevent further damage, as costs and control effectiveness increase over times (Moody & Mack, 1988). ...
There are several techniques for the control and removal of invasive species that can be applied, and there is a demand among restoration practitioners for plant control methods. This study compared two methods for the control of jackfruit tree: mechanical method of trunk girdling and chemical method of herbicide injection into the trunk. It was evaluated both methods in terms of effectiveness in 10 plots (80 × 80 m). For the chemical method, triclopyr in concentrations of 2%, 6% and 8% was used. The progress of treatments was evaluated accordingly for the phytosanitary conditions. Method of trunk girdling proved to be ineffective and it had a low mortality rate (12%). The proportion of dead trees by chemical treatment was 100%. The results showed that chemical control of jackfruit trees was much faster and more effective.
... The conservation of the ancestral niche in the invaded ranges implies that climates between the native and invaded areas are analogous, and thus the likelihood of a successful invasion is high due to the pre-adapted condition of the introduced pool (climate match hypothesis 7 ). Accordingly, the hypothesis of niche conservatism has been extensively used as a proxy to predict the invasion risk of introduced species 8,9 . However, niche conservatism is not always a universal rule applicable to all biological invasions, since the species can grow, survive, or adapt to novel environmental conditions that do not exist in the source area, or that they are available but not yet occupied. ...
One of the topics currently under discussion in biological invasions is whether the species’ climatic niche has been conserved or, alternatively, has diverged during invasions. Here, we explore niche dynamic processes using the complex invasion history model of Lilium lancifolium, which is the first tested case of a native species (Korea) with two hypothesized spatial (regional and intercontinental) and temporal arrivals: (1) as an archaeophyte in East Asia (before AD 1500); and (2) as a neophyte in Europe, North America, Australia, and New Zealand (after AD 1500). Following a niche examination through both environmental and geographical spaces, the species in the archaeophyte range has apparently filled the ancestral native niche and, rather, would have increased it considerably. The species as a neophyte shows a closer climatic match with the archaeophyte range than with the native one. This pattern of niche similarity suggests that the neophyte range was probably colonized by a subset of archaeophyte propagules adapted to local climate that promoted the species’ establishment. Overall, niche conservatism is proposed at each colonization step, from native to archaeophyte, and from archaeophyte to neophyte ranges. We detected signals of an advanced invasion stage within the archaeophyte range and traces of an early introduction stage in neophyte ranges.
... Suitability refers to the degree to which the environment is appropriate for the species in question (Peterson et al., 2011). HSMs provide a step toward modeling habitat shifts under climate change scenarios (Botkin et al., 2007;Carroll et al., 2010;Hannah et al., 2011), predicting hotspots for invasive species (Peterson, 2003;Thuiller et al., 2005;Richardson & Thuiller, 2007), targeting areas for conservation or relocation (Hannah et al., 2002;Thuiller et al., 2004;Fuller et al., 2008;Eigenbrod et al., 2015), evaluating economic impacts to agricultural crops or timber (Hannah et al., 2011(Hannah et al., & 2013Mayer, 2013;Sparks, 2013), and developing metrics to quantify and monitor climate change pressure on tree species (Potter & Hangrove, 2013). The popularity of HSMs has grown dramatically over the past 10 years (e.g., one of the most popular HSMs is MaxEnt (Phillips et al. 2006) which has been cited over 5,000 times in the last 10 years (based on Google Scholar accessed on 16 Feb 2016)). ...
Habitat suitability models (HSMs) are powerful tools that encourage informed decision making in conservation planning, research, and policy making. They are typically derived from the correlation of environmental variables with the location of known species occurrences. Most publications within the last fifty years on HSMs or related habitat modeling techniques do not mention error, noise, or uncertainty. When uncertainty is not reported, these models may elicit a misleading sense of confidence or accuracy in model output. Sources of uncertainty are understood, but the methodology for addressing these sources are not well established. I investigated multiple sources of uncertainty within my data and simulated them using the novel modeling package, Hyper-envelope modeling interface (HEMI 2) for four North American tree species whose geographic ranges are known (redwood, red alder, paper birch, and Douglas-fir). I also investigated the impact of incomplete occurrence data and modeling extent on HEMI 2 using the same species. My study demonstrated that simulating multiple sources of uncertainty within HSMs can increase the coverage of predicted habitat suitability within a species’ geographic range. However, HSMs in general tended to predict a large proportion of potential habitat beyond the documented geographic range of each species. Additionally, HSMs had variable results when this predicted range was compared to each species’ geographic range, regardless of a uniform method for comparison. When manual model adjustment was appropriate, my study also demonstrated that geographic range coverage can increase in accuracy when the species response to its environment is known. With respect to modeling extent, I also found that as it increased beyond the geographic range of each species, the value of habitat suitability tended to decrease. My study provides a comprehensive methodology aimed at quantifying the uncertainty inherit within a few commonly used data sources (FIA, WorldClim, and BioClim), where my results support the overall importance of modeling uncertainty in HSMs.
... At the same time, forest restoration and native tree plantations are an interesting alternative for control of A. mangium and A. auriculiformis, since forest fragments act as a barrier to these species and they are not able to grow under dense canopy (Delnatte and Meyer 2012). However, in regions where A. mangium is not currently reported as invasive, but that have high suitability in the future scenarios, the installation of Acacia plantations should be carefully evaluated, because these plantations increase propagule pressure (Richardson and Thuiller 2007;Donaldson et al. 2014) in a hotspot full of pathways for invasive acacias due deforestation and land-use changes. ...
Climate change and biological invasions are two of the most cited factors that may affect species diversity in the coming decades. Here we used five climate scenarios to investigate the potential distribution of two invasive tree species, Acacia mangium and A. auriculiformis, in the Atlantic Forest hotspot. Additionally, we used expansion–contraction maps and maps of potential areas for forest restoration to investigate whether biological invasion could affect restoration efforts. We found A. mangium has a large suitable area in all scenarios (average 268,010.1 km² ± 25,292.4 SD), while A auriculiformis is confined to a relatively small region (average 13,123.1 km² ± 361.7 SD). In the low greenhouse gas emissions scenario (RCP 2.6), the suitable area for A. mangium varied from the current scenario of 24.8% of the Atlantic Forest to 26.2% and 25.4% in the years 2050 and 2070, respectively. In the high greenhouse gas emission scenario (RCP 8.5), the suitable area contracted to 23.1% and 20.5% in 2050 and 2070, respectively. Approximately 30.8% of the potential area for restoration currently overlaps the suitable area for A. mangium, and this overlap reaches at least 23.8% of the potential areas for restoration in the future scenarios (RCP 8.5 in 2070). A. mangium has a large suitable area in the Atlantic Forest and can become a barrier to restoration efforts in the coming decades. Expansion–contraction maps should be used to establish environmental policies that promote both forest restoration and prevention of biological invasion in suitable areas.
... Among regions that have received imports of Australian acacias, perhaps none is more suitable in terms of broad-scale bioclimatic conditions than South Africa. All of South Africa's seven biomes have equivalent bioclimatic zones in Australia, and Australia has more than four times the land area with South Africa-like climate than exists in South Africa (Richardson & Thuiller, 2007). Broad-scale climatic matching is widely recognized as a fundamental requirement for the success of introduced plants. ...
Aim Australian acacias (1012 recognized species native to Australia, which were previously grouped in Acacia subgenus Phyllodineae) have been moved extensively around the world by humans over the past 250 years. This has created the opportunity to explore how evolutionary, ecological, historical and sociological factors interact to affect the distribution, usage, invasiveness and perceptions of a globally important group of plants. This editorial provides the background for the 20 papers in this special issue of Diversity and Distributions that focusses on the global cross-disciplinary experiment of introduced Australian acacias. Location Australia and global. Methods The papers of the special issue are discussed in the context of a unified framework for biological invasions. Distributions of species were mapped across Australia, their representation in bioclimatic zones examined and the potential global distribution of the group modelled. By collating a variety of different lists, we determined which Australian acacias have reached different stages in the introduction-naturalization-invasion continuum in different parts of the world. Paradigms and key research questions relating to barriers to invasion, stages of invasion and management perceptions are sketched. Results According to our global database of Australian acacia records, 386 species have been moved outside Australia by human agency, 71 species are naturalized or weedy, and 23 are unequivocally invasive. Climatic models suggest that about a third of the world's land surface is climatically suitable for Australian acacias. Many species are commercially important crops or are useful for other purposes and have been extensively planted, and many different human perceptions of Australian acacias exist in different parts of the world. The papers in the special issue cover all the barriers, stages and processes that define biological invasions and touch on many aspects: history and the human dimension; aspects of the species pool; species traits; biotic interactions; climate and niche; and management. Main conclusions Australian acacias are an excellent model group for examining interactions between evolutionary, ecological and socioeconomic drivers of species introductions. New insights have emerged on the biological, ecological and evolutionary correlates of naturalization and invasion, but human usage factors permeate all explanatory models. Understanding and managing introduced Australian acacias requires a fundamental and integrative appreciation of both intrinsic (e.g. species traits) and extrinsic (e.g. human usage and perceptions) aspects.
... The observed variation in invasiveness of Australian acacias clearly depends on a complex interplay of factors, including functional traits, dispersal strategies, climate similarity between Australia and recipient areas, as well as numerous extrinsic factors (e.g. Thuiller et al., 2006;Richardson & Thuiller, 2007;Wilson et al., 2007;Gallagher et al., 2011;Gibson et al., 2011). In this paper, however, we focus on exploring whether macroecological patterns of acacia distribution in their native range could potentially provide a simple accumulated index that would assist in predicting the probability of them becoming invasive. ...
Aim Species’ native ranges reflect the net outcome of interactions between life‐history strategies and biotic and abiotic influences over evolutionary time‐scales. Differences in native ranges might be indicative both of relative historical performance and adaptability to new conditions. Consequently, the native ranges of successful invaders might have distinctive biogeographical characteristics. We test this hypothesis by (1) quantifying macroecological patterns of the entire assemblage of native taxa in Acacia subgenus Phyllodineae in Australia, (2) testing whether highly invasive taxa represent random samples from the patterns observed for the assemblage as a whole and (3) exploring the link between native geographical range and the position of species along the introduction‐naturalization‐invasion continuum.
Location Australia and worldwide.
Methods Three distributional metrics representing particular biogeographical characteristics of species’ native ranges – the logarithms of range size, percolation intercept and percolation exponent – were calculated by fitting a revised alpha hull to records from Australia’s Virtual Herbarium. Randomization and cascaded tests were used to compare these metrics for species at different stages of invasion.
Results The macroecological patterns of the three distributional metrics displayed lognormal‐like frequency distributions. Most invasive species had significantly lower percolation exponents and larger native ranges than expected from random draws from the entire assemblage of Australian acacias, but percolation intercepts were not significantly different. This can be explained by a selection bias at the early stages of invasion.
Main conclusions The outcome of the natural experiment of transplanting many Australian acacias into novel environments is not random. While invasive species have a particular macroecological pattern, this can be explained by the observation that species with large native ranges and low percolation exponents (i.e. high population increase rate) are most likely to have been introduced and naturalized. Whether this pattern is an artefact of human selection or reflects a human bias towards selecting invasive species remains to be seen.
... As a minimal standard, use published maps of climate zones to check whether the climate in the Area is suitable for the Taxon. Such maps include the following: -Koeppen-Geiger climate zones, updated by Peel et al. (2007) - Richardson and Thuiller (2007) maps of global locations that match South African climates Climate models are more desirable and lead to a higher confidence in the assessment. If the Area encompasses multiple climate zones, consider those that are most likely suited and mention in the comments section which climatic zones were assessed. ...
This report presents a framework for analysing the risk of alien taxa under South Africa's National Environmental Management: Biodiversity Act of 2004, and the Alien and Invasive Species Regulations of 2014. While the report was initially designed to meet a specific South Africa need, the risk analysis processes developed can, we believe, be transferred to any specified geographic region. In outlining a series of questions related to a taxon’s likelihood of invasion and the consequences thereof, i.e. the potential impacts, the report provides a structure for collating data relevant to the process of listing taxa as well as a process for developing recommendations that is both mathematically sound, transparent, and that explicitly takes uncertainty into account. The framework is based on collating information according to international standards in biological invasions (specifically the IUCN Environmental Impact Classification of Alien Taxa Scheme, the CBD's scheme for classifying invasion pathways, and the Unified Framework for Biological Invasions proposed by Blackburn et al. 2011). The risk analysis framework is currently being implemented in South Africa in an effort to underpin national regulatory lists of invasive species.
... Species distribution modelling (SDM), although applied to plant species for more than twenty years (Box, 1981;Busby, 1986) and constrained in a number of ways (Pearson & Dawson, 2003;Araújo & New, 2007;Heikkinen et al., 2006), is now widely acknowledged as the most effective tool to use for initial assessment of species responses to climate change. Over the past decade these methods have been applied to invasive species in various parts of the world (Le Maitre et al., 2008;Richardson & Thuiller, 2007;Peterson, 2003;Richardson & Rejmánek, 2004;Rouget et al., 2004). With the exception of Scott et al. (2008) and Steel et al. (2008) most modelling of non-native plant species in Australia has been undertaken for relatively few weed species (Chejara et al., 2010;Kriticos et al., 2010;Kriticos et al., 2009;Kriticos et al., 2000;Kriticos et al., 2003b;Kriticos et al., 2003a;Kriticos et al., 2011;Kriticos et al., 2005;Potter et al., 2009;Watt et al., 2010;Beaumont et al., 2009a), or on a regional basis Steel et al., 2008). ...
Summary
Weeds and climate change are both significant threats to biodiversity and pose considerable challenges to managers of protected areas, such as national parks. Weeds are likely to respond to climate and atmospheric change (e.g. increased temperatures, changed rainfall patterns, and elevated CO2 levels) in complex ways but knowledge as to the magnitude and direction of these responses is very limited.
Species distribution models (SDMs) based primarily on climate data provide a first-step tool for assessing potential changes in the geographic range of species under climate change. These models can play an integral part in developing proactive management strategies for current and emerging weed threats.
We produced SDMs for 107 terrestrial and aquatic non-native plant species in Australia which incorporates the 20 Weeds of National Significance (WoNS), the WoNS shortlist, the National Alert List, and four major invasive grass species using the MaxEnt modelling program. Species location data came primarily from publicly available herbarium records. We built our models on the baseline climate of the late 20th Century provided by the WorldClim data set, and projected these models onto averaged future climate in three decades centred on 2020, 2050 and 2080. The latest climate data from the Inter-governmental Panel on Climate Change (IPCC) repository for the IPCC Fourth Assessment Report (AR4) was used for models of future climate. We also developed several novel ways of presenting and interpreting the data generated.
The results suggest two broad patterns of change:
Species with extensive current distributions in northern Australia are predicted to encounter increasingly favourable environmental conditions and are likely to extend their geographical range and/or become more abundant within existing locations.
Most species in south-east Australia are predicted to encounter much less suitable climatic conditions and are likely to show a south-east geographic range shift and/or decrease in climatic suitability.
There are two important points to note. First, many of the modelled species have not yet reached their potential distribution under current climate conditions and therefore the distribution and abundance of species may continue to increase from current locations despite a predicted reduction in favourable conditions under future climate. Second, the 107 species modelled are a small proportion of the pool of more than 2,800 naturalised plants species present in Australia. At least 12 new species are added to this naturalised species pool each year. In order to manage protected areas for biodiversity conservation under future climates, it is critical to assess the threat from these potential future weed species in addition to the 107 nationally-recognized species modelled here.
The methods we have developed can be used to rapidly and efficiently screen this pool of naturalised exotic species to provide indications of emerging threats to biodiversity under climate change.
The initial modelling presented in this report can be used to:
develop weed threat scenarios at a range of geographic levels and management areas (e.g. individual national parks, catchments or other areas of interest), and
identify future ―"invasion hotspots" to help prioritise control and resources, as well as limit impacts.
The emerging alien cactus Cylindropuntia pallida (Rose) F.M. Knuth originates from northern Mexico and introduced into South Africa in 1940s as an ornamental plant. Multiple populations of C. pallida have been detected in various areas of South Africa. C. pallida has effective propagule dispersal and rapid recruitment making it a likely key future invader, and thus, is a target for eradication in South Africa. To eradicate C. pallida populations, a foliar spray (i.e. using a 2% concentration of herbicide with fluroxypyr and triclopyr) has been applied to plants in nine populations, with population sizes ranging between 535 and 2701 plants and populations covering areas of 100 –1000 ha. The aims of the study were to investigate the efficacy of the foliar spray method used to eradicate C. pallida; to investigate the impacts of C. pallida invasions on native vegetation integrity; to apply species distribution models (SDMs) to identify suitable climates for C. pallida in South Africa; and to document the biomes vulnerable to the negative impact of C. pallida in South Africa. Results show that foliar spray killed many C. pallida plants (mean percentage of dead plants ± SE, 83.3 ± 6.4; n = 9; range, 70–96%), with adult plants taking about 2 months to die completely. The efficacy of the herbicide was not affected by plant size or the concentration of the herbicide used. The invaded site had significantly greater vegetation cover which persisted across winter compared to the uninvaded site, but the latter site’s vegetation cover significantly dropped in winter. Also, the invaded site had lower plant species diversity than the uninvaded site and was dominated by species in the Poaceae and Asteraceae plant families. Additionally, a normalised difference vegetation index (NDVI) analysis shows that the uninvaded site has higher vegetation cover and health than the invaded site wherein a notable decline in vegetation health was observed between 2019 and 2022. A large area (> 15 million hectares) was predicted to be suitable for invasion by C. pallida in provinces with arid and warm temperate climates - the fynbos and grassland biomes are the most vulnerable. Because of the observed negative impacts, high environmental compatibility, and high cost of clearing large infestations, we advocate for considering the biocontrol method for effectively managing C. pallida invasion in South Africa.
The benefits of early detection of biological invasions are widely recognized, especially for protected areas (PAs). However, research on incipient invasive plant species is scarce compared to species with a recognized history of invasion. Here, we characterized the invasion status of the non-native conifer Juniperus communis in PAs and interface areas of Andean Patagonia, Argentina. We mapped its distribution and described both the invasion and the environments this species inhabits through field studies, a literature review, and a citizen science initiative. We also modeled the species' potential distribution by comparing the climatic characteristics of its native range with those of the introduced ranges studied. The results show that J. communis is now widely distributed in the region, occurring naturally in diverse habitats, and frequently within and close to PAs. This species can be considered an incipient invader with a high potential for expansion in its regional distribution range, largely due to its high reproductive potential and the high habitat suitability of this environment. Early detection of a plant invasion affords a valuable opportunity to inform citizens of the potential risks to high conservation value ecosystems before the invader is perceived as a natural component of the landscape. Access: https://rdcu.be/deKrD
Introducción y objetivos: La información sobre la biodiversidad de áreas protegidas es fundamental para desarrollar estrategias de manejo y conservación. En este trabajo evaluamos el número de registros de plantas y vertebrados de Parques Nacionales (PN) de Argentina en función de la riqueza de especies de la provincia donde se encuentra cada PN, analizamos posibles variables explicativas del número de registros en cada PN, y describimos la vegetación registrada en tres PN icónicos del país.
M&M: Los registros de plantas vasculares y de vertebrados, las características de cada PN y la riqueza de especies de la provincia donde se encuentra cada PN se obtuvieron de bases de datos de acceso abierto. Para los PN Calilegua, Iguazú y Nahuel Huapi describimos el número de plantas según familia, origen, endemismo, forma de vida, estado de conservación según UICN e invasividad de especies no nativas.
Resultados: Los PN presentan gran variabilidad en sus registros. Existen pocos registros de especies no nativas. Los PN más antiguos registraron más plantas no nativas. La lista de plantas del PN Nahuel Huapi mostró un mayor número de registro que Calilegua e Iguazú. El número de plantas categorizadas por UICN es muy bajo. Casi todas las plantas no nativas registradas son invasoras en otros lugares del mundo.
Conclusiones: Destacamos la importancia de incrementar el relevamiento de especies en todos los PN, particularmente de plantas y en PN de reciente creación. Se requiere mayor atención a especies no nativas a fin evitar problemas socio-ecológicos asociados a invasiones biológicas.
The natural and semi-natural ecosystems of dry tropical regions are characterized by a high biodiversity with the new introduction of alien invasive species, especially at disturbed sites. The tropical regions due to favorable environmental conditions are considered rich reservoirs of much of the biodiversity of the earth. The Indian dry tropical urban region has also been reported to be highly diverse but fragile with abundant alien flora, of which American, Asian, and European and Asian species form the major contributions. By the allelopathic activity, these weeds alter the soil environment, cause low productive systems with weak soil microflora and accelerate their fast spread by fast colonization, fast reproduction, or highly competitive ability. These weedy species have a great potential to make persistent soil seed banks. The soil seed bank is a reservoir of viable but ungerminated seeds and acts as a genetic reservoir that could play an important role in determining the future vegetation of the community. The present study carried out four different land use patterns and focused on the seed bank dynamics of these sites. In this study, the abundance of alien invasive species in the floristic composition and density of the subterranean vegetation reflects the impact of disturbance and other anthropogenic factors.
Oenothera drummondii is a coastal dunes plant species from the North American continent that has affected the natural structure and dynamics of Spanish, Israeli, and Chinese shores as an invasive species. In South Africa, Australia, New Zealand, and France, it is reported as a naturalized species. Ecological niche and species distribution modeling has been widely used as a tool to find potential global invasions and assess invasion effects. Herein, we modeled the ecological niche and the potential distribution of Oenothera drummondii, using the Köppen–Geiger climate classification, bioclimatic variables and occurrence records that have been validated in their native and non-native distribution. In the native area, the temperature and precipitation values are higher compared to non-native zones, where the low temperatures and the absence of humidity are the main climatic limitations for the species. In the environmental space, new distribution areas were identified and a partial overlap between the native and non-native niches detected. This suggests that climate matching is not occurring for the species, and that the potential invasion of coastal dune areas seems to be higher than previously observed. Therefore, new potential invasion areas, where the species is not yet distributed, were also identified. Our predictions could be used to establish ecosystem management measures to mitigate the invasion of Oenothera drummondii, helping to prevent possible negative impacts on fragile coastal ecosystems.
The Peruvian Peppertree ( Schinus molle L.) is an evergreen tree native to semiarid environments of Peru and Bolivia in South America. This tree has been introduced and widely planted for ornamental and forestry purposes in several semiarid regions of the world because its seedlings are easily established and have a high survival rate; it also grows quickly, and it is tolerant of dry climates. We compared the global and regional niches of naturalized and planted populations of S. molle in order to examine the invasive stages and potential distribution of this species in four regions of the world. This work provides a novel approach for understanding the invasion dynamics of S. molle in these areas and elucidates the ecological processes that bring about such invasions. Most naturalized and planted populations were found to be in equilibrium with the environment. In its native range as well as in Australia and South Africa the models of the coverage area of habitat suitability for natural populations were the highest, whereas the coverage area of planted populations was lower. For planted populations in Australia and South Africa, a large percentage of predicted presences fell within sink populations. The invasion stages of S. molle vary across regions in its adventive range; this result may be attributable to residence time as well as climatic and anthropic factors that have contributed to the spread of populations.
Pale swallow-wort, Vincetoxicum rossicum (Kleopow) Barbar., is an invasive weed in the lower Great Lakes Basin of North America. We investigated the relationship between V. rossicum productivity and several environmental variables across 54 established V. rossicum populations in southern Ontario. Variables included climate measurements, soil characteristics (pH, texture, and nutrient status), habitat type, plant community, and the diversity of root-associated fungi. Vincetoxicum rossicum roots were collected at all 54 sites, and associated fungi were compared using terminal restriction fragment length polymorphism. Aboveground biomass of V. rossicum was measured at 23 sites with similar light regimes, allowing comparison between populations. Results suggested that abiotic soil variables, and habitat type have little effect on V. rossicum productivity. Aboveground biomass production was significantly correlated with precipitation, and the presence of fungal pathogens and dark septate endophytes. Annual precipitation and soil clay content were also positively correlated with the abundance of soil pathogens. Accumulation of these microbes may negatively affect co-occurring native plants and associated fungal partners. The presence of these fungal species in soil could be used as an indicator of site susceptibility to invasion by V. rossicum and assist in the development of management plans for this exotic vine.
Human livelihoods and well-being in almost all regions of the world depend on taxa which are alien. Such taxa also, however, threaten human health, sustainable development, and biodiversity. Since it is not feasible or desirable to control all alien taxa, decision-makers increasingly rely on risk analyses to formalise the best available evidence of the threats posed and whether and how they can be managed. There are a variety of schemes available that consider the risks of alien taxa, but we argue a new framework is needed: 1) given major recent developments in international frameworks dealing with biological invasions (including the scoring of impacts); 2) so that decisions can be made consistently across taxa, regions and realms; 3) to explicitly set out uncertainties; and 4) to provide decision-makers with information both on the risks posed and on what can be done to mitigate or prevent impacts. Any such scheme must also be flexible enough to deal with constraints in capacity and information. Here we present a framework to address these points – the Risk Analysis for Alien Taxa (RAAT). It outlines a series of questions related to an alien taxon’s likelihood of invasion, realised and potential impacts, and options for management. The framework provides a structure for collating relevant data from the published literature to support a robust, transparent process to list alien taxa under legislative and regulatory requirements, with the aim that it can be completed by a trained science graduate within a few days. The framework also provides a defensible process for developing recommendations for the management of assessed taxa. We trialled the framework in South Africa and outline the process followed and some of the taxa assessed to date.
Global changes and their impacts on biodiversity are currently attracting a great deal of
attention from the scientific community and natural ecosystem managers. The monitoring of land use changes is identified by the Global Climate Observing System (GCOS) as one of the five High Priority Climate Variables (VCEs).
The steppe occupies the majority of the southern high plains of South Algeria with steppe
plant communities such as Stipa tenacissima, Artemisia herba-alba and Ziziphus lotus groups.
Fieldwork has reported the isolation of people in these areas with no basic social infrastructure.
The prediction of land-use changes has provided an opportunity to assess the expansion,
regression and future stability of each type of occupation. Seven individual models were used to generate the suitability maps for each land use type of Zahrez El Gharbi, characterized by occurrence suitability values. In order to resolve their degrees of uncertainty, the combination of the individual models led to the development of seven consensus methods. The predictive performance of individual models and consensus methods was evaluated by the Area Under Curve (AUC) calculation. Finally, the CA-Markov model was used to model the land use map for 2045 on a trend scenario.
The results showed that there will be very important transitions between land use classes.
Urban agglomerations would be expanded by 3,695 ha on the expanse of other ccupancy
classes while keeping their present surface area, moreover courses would also have a positive change by gaining large areas, however this class would lose large areas in turn, in other words, the steppe would lose its current surface and gain other environments. The most
alarming finding of future change is the degradation of the forest; this occupation class will lose
more than 10,200 ha, the predicted regression insists on the immediate implementation of an
integrated territorial management plan.
The approach used in this work has predicted changes in each type of occupation by
integrating physical and anthropogenic factors and can support planners and managers inwords conserving natural resources and improving long-term territorial management
South Africa is a megadiverse country in terms of biodiversity, with continental South Africa composed of nine terrestrial biomes. This diversity is in part due to the wide range of climatic and topographic conditions that exist in the country. This chapter explores how these environmental features influence biological invasions (focusing on terrestrial ecosystems). We first discuss broad features of the different landscapes, and then discuss how different environmental factors [geomorphology, soils, climate (including rainfall seasonality), extreme events (specifically droughts and floods), fire, freshwater, and land use] determine which species can establish, spread, and cause adverse impacts. The high diversity of invasive species in South Africa is partly due to the variety of environmental conditions, but some conditions (e.g. fire and aridity) also limit invasions. With reference to plants, invasive species assemblages seem to be co-incident with native species assemblages at a broad-scale (although the driving mechanisms are unclear). However, finer-scale influences of anthropogenic factors (e.g. introduction effort and disturbance) also play important roles in shaping invasive biotas. Together these factors suggest that climate-based species distribution models (with an additional fire filter) can accurately predict the broad-scale potential range of invaders in South Africa. However, at finer scales and for management purposes, we need to understand how humans directly and indirectly influence patterns of invasion.
Thousands of plant species have been introduced, intentionally and accidentally, to South Africa from many parts of the world. Alien plants are now conspicuous features of many South African landscapes and hundreds of species have naturalised (i.e. reproduce regularly without human intervention), many of which are also invasive (i.e. have spread over long distances). There is no comprehensive inventory of alien, naturalised, and invasive plants for South Africa, but 327 plant taxa, most of which are invasive, are listed in national legislation. We collated records of 759 plant taxa in 126 families and 418 genera that have naturalised in natural and semi-natural ecosystems. Over half of these naturalised taxa are trees or shrubs, just under a tenth are in the families Fabaceae (73 taxa) and Asteraceae (64); genera with the most species are Eucalyptus, Acacia, and Opuntia. The southern African Plant Invaders Atlas (SAPIA) provides the best data for assessing the extent of invasions at the national scale. SAPIA data show that naturalised plants occur in 83% of quarter-degree grid cells in the country. While SAPIA data highlight general distribution patterns (high alien plant species richness in areas with high native plant species richness and around the main human settlements), an accurate, repeatable method for estimating the area invaded by plants is lacking. Introductions and dissemination of alien plants over more than three centuries, and invasions over at least 120 years (and especially in the last 50 years) have shaped the distribution of alien plants in South Africa. Distribution patterns of naturalised and invasive plants define four ecologically-meaningful clusters or “alien plant species assemblage zones”, each with signature alien plant taxa for which trait-environment interactions can be postulated as strong determinants of success. Some widespread invasive taxa occur in high frequencies across multiple zones; these taxa occur mainly in riparian zones and other azonal habitats, or depend on human-mediated disturbance, which weakens or overcomes the factors that determine specificity to any biogeographical region.
The vast colonisation of some wetlands by Cyclosorus afer in Lafia, Nigeria has been a serious concern to ecologists and indigenous dwellers. In this study, we used the Maximum Entropy (Maxent) modelling technique to predict the habitat suitability of this fern in Lafia, Nigeria. We obtained the presence data of this fern in three already invaded wetlands of size 500 x 500m2 each using multiple 200m transect. Bioclimatic and elevation variables which were obtained from different databases were imputed into the model as predictor variables of C. afer. After that, the Maxent model was run with 70% of the presence data as training and 30% as test data. Our model result revealed that the area under the curve for receiver operating characteristics of training is 0.847 while and test data is 0.970. The model’s sensitivity was observed to be 100%. The model was assessed based on a jackknife test of individual contributions of each predictor variable to the model. Therefore, the environmental predictors of the occurrence of C. afer in this study area include precipitation seasonality, Precipitation of driest quarter, precipitation of coldest quarter and elevation. This model could be described as accurate, and the occurrence of C. afer in Lafia, Nigeria, is influenced by limiting environmental factors
With climate change and increasing globalisation of trade and travel, the risks presented by invasive pests and pathogens to natural environments, agriculture and economies have never been greater, and are only increasing with time. Governments world-wide are responding to these increased threats by strengthening quarantine and biosecurity. This book presents a comprehensive review of risk-based techniques that help policy makers and regulators protect national interests from invasive pests and pathogens before, at, and inside national borders. Selected from the research corpus of the Centre of Excellence for Biosecurity Risk Analysis at the University of Melbourne, this book provides solutions that reflect scientific rigour coupled with practical, hands-on applications. Focusing on surveillance, stochastic modelling, intelligence gathering, decision making and risk communication, the contents combine the strengths of risk analysts, mathematicians, economists, biologists and statisticians. The book presents tested scientific solutions to the greatest challenges faced by quarantine and biosecurity policy makers and regulators today.
A subset of invasive alien plant species in southern Africa was analysed in terms of their history of introduction, rate of spread, countries/region of origin, taxonomy, growth forms, cultivated uses, weed status and current distribution in southern Africa, and comparisons made of those originating from south of the tropic of Capricorn, north of the tropic of Cancer and from the tropics. The subset of 233 species, belonging to 58 families, includes all important declared species and some potentially important species. Almost as many species originate from temperate regions (112) as from the tropics (121). Most southern temperate species came from Australia (28/36), most tropical species from tropical America (92/121) and most northern temperate species from Europe (including the Mediterranean) and Asia (58/76). Transformers account for 33% of all species. More transformers are of tropical origin (36) than of northern temperate (24) and southern temperate origin (18). However, 50% of southern temperate species are transformers, compared to 32% of northern temperate and 29% of tropical species. Southern temperate transformer species are mainly woody trees and shrubs that were established on a grand scale as silvicultural crops, barriers (hedges, windbreaks and screens) and cover/binders. Most aquatics, herbs, climbers and succulent shrubs are from the tropics. Ornamentals are the single largest category of plants from all three regions, the tropics having contributed twice as many species as temperate regions.
A new computation framework (BIOMOD: BIOdiversity MODelling) is presented, which aims to maximize the predictive accuracy of current species distributions and the reliability of future potential distributions using different types of statistical modelling methods. BIOMOD capitalizes on the different techniques used in static modelling to provide spatial predictions. It computes, for each species and in the same package, the four most widely used modelling techniques in species predictions, namely Generalized Linear Models (GLM), Generalized Additive Models (GAM), Classification and Regression Tree analysis (CART) and Artificial Neural Networks (ANN). BIOMOD was applied to 61 species of trees in Europe using climatic quantities as explanatory variables of current distributions. On average, all the different modelling methods yielded very good agreement between observed and predicted distributions. However, the relative performance of different techniques was idiosyncratic across species, suggesting that the most accurate model varies between species. The results of this evaluation also highlight that slight differences between current predictions from different modelling techniques are exacerbated in future projections. Therefore, it is difficult to assess the reliability of alternative projections without validation techniques or expert opinion. It is concluded that rather than using a single modelling technique to predict the distribution of several species, it would be more reliable to use a framework assessing different models for each species and selecting the most accurate one using both evaluation methods and expert knowledge.
We examine the consequences of restricting the range of environmental conditions over which niche-based models are developed to project potential future distributions of three selected European tree species to assess first, the importance of removing absences beyond species known distributions (“naughty noughts”) and second the importance of capturing the full environmental range of species. We found that restricting the environmental range of data strongly influenced the estimation of response curves, especially towards upper and lower ends of environmental ranges. This induces changes in the probability values towards upper and lower environmental boundaries, leading to more conservative scenarios in terms of changes in distribution projections.
Using restricted data analogous to not capturing the fun species’ environmental range, reduces strongly the combinations of environmental conditions under which the models are calibrated, and reduces the applicability of the models for predictive purposes. This may generate unpredictable effects on the tails of the species response curves, yielding spurious projections into the future provided that probability of occurrence is not set to zero outside the environmental limits of the species. Indeed, as the restricted data does not capture the whole of the response curve, projections of future species distributions based of ecological niche modelling may be only valid if niche models are able to approach the complete response curve of environmental predictors.
Recent observations show that human-induced climate change (CC) and land transformation (LT) are threatening wildlife globally. Thus, there is a need to assess the sensitivity of wildlife on large spatial scales and evaluate whether national parks (NPs), a key conservation tools used to protect species, will meet their mandate under future CC and LT conditions. Here, we assess the sensitivity of 277 mammals at African scale to CC at 10′ resolution, using static LT assumptions in a ‘first-cut’ estimate, in the absence of credible future LT trends. We examine the relationship between species' current distribution and macroclimatic variables using generalized additive models, and include LT indirectly as a filter. Future projections are derived using two CC scenarios (for 2050 and 2080) to estimate the spatial patterns of loss and gain in species richness that might ultimately result. We then apply the IUCN Red List criteria A3(c) of potential range loss to evaluate species sensitivity. We finally estimate the sensitivity of 141 NPs in terms of both species richness and turnover. Assuming no spread of species, 10–15% of the species are projected to fall within the critically endangered or extinct categories by 2050 and between 25% and 40% by 2080. Assuming unlimited species spread, less extreme results show proportions dropping to approximately 10–20% by 2080. Spatial patterns of richness loss and gain show contrasting latitudinal patterns with a westward range shift of species around the species-rich equatorial zone in central Africa, and an eastward shift in southern Africa, mainly because of latitudinal aridity gradients across these ecological transition zones. Xeric shrubland NPs may face significant richness losses not compensated by species influxes. Other NPs might expect substantial losses and influxes of species. On balance, the NPs might ultimately realize a substantial shift in the mammalian species composition of a magnitude unprecedented in recent geological time. To conclude, the effects of global CC and LT on wildlife communities may be most noticeable not as a loss of species from their current ranges, but instead as a fundamental change in community composition.
This paper demonstrates the use of a bioclimatic model mapped over geographical regions as a tool for spatially refined risk assessment for the establishment of non-indigenous plants with invasive behaviour. Drawing on the relationship between plant distribution and climate, the approach uses gridded spatial interpolated monthly means of temperature and precipitation linked with accurate maps of general native distribution ranges to predict the long-term potential of a plant species to invade a certain region. The ascertained potential for establishment is illustrated by the example of garlic mustard (Alliaria petiolata[M. Bieb.] Cavara & Grande) in North America. The first step is to calculate and visualize the number of populated grid cells along climatic gradients in frequency diagrams for the general native distribution range. Interpretations of the response curves recorded are used for assessing apparent climatic range boundaries. Modelling was gradually optimized based on the results of experience-based interpretations and by examining omission and over-representation errors. The obtained climatic model of the range of A. petiolata shows considerable congruencies with its mapped, native Eurasian range. Degrees of climatic similarity between North America and the native range of A. petiolata were calculated with the help of GIS methodology and were used to assess the regionally different likelihood of establishment in North America of the invasive species under consideration.
In a field experiment with 30 locally occurring old-field plant species grown in a common garden, we found that non-native plants suffer levels of attack (leaf herbivory) equal to or greater than levels suffered by congeneric native plants. This phylogenetically controlled analysis is in striking contrast to the recent findings from surveys of exotic organisms, and suggests that even if ‘enemy release’ does accompany the invasion process, this may not be an important mechanism of invasion, particularly for plants with close relatives in the recipient flora.
Increasing concern over the implications of climate change for biodiversity has led to the use of species–climate envelope models to project species extinction risk under climate-change scenarios. However, recent studies have demonstrated significant variability in model predictions and there remains a pressing need to validate models and to reduce uncertainties. Model validation is problematic as predictions are made for events that have not yet occurred. Resubstituition and data partitioning of present-day data sets are, therefore, commonly used to test the predictive performance of models. However, these approaches suffer from the problems of spatial and temporal autocorrelation in the calibration and validation sets. Using observed distribution shifts among 116 British breeding-bird species over the past ∼20 years, we are able to provide a first independent validation of four envelope modelling techniques under climate change. Results showed good to fair predictive performance on independent validation, although rules used to assess model performance are difficult to interpret in a decision-planning context. We also showed that measures of performance on nonindependent data provided optimistic estimates of models' predictive ability on independent data. Artificial neural networks and generalized additive models provided generally more accurate predictions of species range shifts than generalized linear models or classification tree analysis. Data for independent model validation and replication of this study are rare and we argue that perfect validation may not in fact be conceptually possible. We also note that usefulness of models is contingent on both the questions being asked and the techniques used. Implementations of species–climate envelope models for testing hypotheses and predicting future events may prove wrong, while being potentially useful if put into appropriate context.
Prediction of species’ distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species’ distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species’ occurrence data. Presence-only data were effective for modelling species’ distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.
Any organism must be equipped for life in a given environment, otherwise it will die. The fundamental question is how well does an organism need to be “equipped”,or what syndrome of traits must it possess to survive and flourish at a given locality.
In the current human-mediated biodiversity crisis, where alien species play an important role, we need to know whether some
species are inherently better equipped to become invasive when moved to new areas by humans. If so, we can identify such species
and consider management options to prevent, or at least reduce the damaging effects of biological invasions.
Despite the importance of chance and timing in the establishment and spread of alien plants (Crawley 1989), invasions are
clearly not entirely random events (Crawley et al. 1996). Much of the early work on invasions was directed at collating traits
associated with invasiveness (Booth et al. 2003). The question of whether is it possible to determine a set of traits that
predispose a species to be invasive has been a central theme since the emergence of invasion ecology as a discrete field of
study.
In the last two decades, interest in species distribution models (SDMs) of plants and animals has grown dramatically. Recent advances in SDMs allow us to potentially forecast anthropogenic effects on patterns of biodiversity at different spatial scales. However, some limitations still preclude the use of SDMs in many theoretical and practical applications. Here, we provide an overview of recent advances in this field, discuss the ecological principles and assumptions underpinning SDMs, and highlight critical limitations and decisions inherent in the construction and evaluation of SDMs. Particular emphasis is given to the use of SDMs for the assessment of climate change impacts and conservation management issues. We suggest new avenues for incorporating species migration, population dynamics, biotic interactions and community ecology into SDMs at multiple spatial scales. Addressing all these issues requires a better integration of SDMs with ecological theory.
Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well-known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high-risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility. The close match that we found between the climatic component of the ecological habitat suitability and the current pattern of occurrence of South Africa alien species in other parts of the world is encouraging. If species' distribution data in the donor country are available, climatic niche modelling offers a powerful tool for efficient and unbiased first-step screening. Given that eradication of an established invasive species is extremely difficult and expensive, areas identified as potential new sites should be monitored and quarantine measures should be adopted.
Plant species continue to be introduced in North America for various purposes. If the trend continues, it is probable that some will escape cultivation and become invasive in native ecosystems. We present a retrospective analysis of several structural, life history, and biogeographical attributes of woody plants introduced in North America to determine which traits characterize species that have and have not invaded. Predictive models derived from discriminant analysis correctly classified 86.2% of the species in cross-validation, whereas those derived from classification and regression trees classified 76% correctly. From these models we created a hierarchical predictive tree that allows the user to divide species into three categories: admit (low risk of invasiveness), deny admission (high risk of invasiveness), or delay admission for further analyses and/or monitor intensively (risk cannot adequately be assessed based on only the included attributes). We recommend that species that are highly invasive elsewhere not be allowed into the U.S. and that a more conservative introduction policy using a hierarchical predictive method be employed.
. Comparisons of the positions of species on Grimes'C-S-R triangular ordination model with their responses to individual environmental gradients indicates that the C-S-R model does not necessarily predict species ecological behaviour. The importance of the stress, productivity and disturbance gradients relative to other environmental gradients needs to be determined. In studies of species behaviour along a biomass/productivity gradient the collective vegetation property, biomass, has been confused with the environmental factor, fertility. Patterns of responses to biomass gradients e.g. Keddy's centrifugal model, should be examined in a two-dimensional environmental space to avoid such confounding effects. Assumptions regarding the shapes of species responses to environmental gradients remain untested. A recent model of species response functions to environmental gradients suggested that skewed responses curves show a pattern in the direction of the skew, always with the tail towards the presumed most mesic position on the gradient. Further evidence is presented to support this model for a temperature gradient in eucalypt forest in south-eastern Australia. 21 out of 24 species tested conform to the model.
A new predictive modelling technique called the fuzzy envelope model (FEM) is introduced. The technique can be used to predict potential distributions of organisms using presence-only locality records and a set of environmental predictor variables. FEM uses fuzzy logic to classify a set of predictor variable maps based on the values associated with presence records and combines the results to produce a potential distribution map for a target species. This technique represents several refinements of the envelope approach used in the BIOCLIM modelling package. These refinements are related to the way in which FEMs deal with uncertainty, the way in which this uncertainty is represented in the resultant potential distribution maps, and the way that these maps can be interpreted and applied. To illustrate its potential use in biogeographical studies, FEM was applied to predicting the potential distribution of three invasive alien plant species (Lantana camara L., Ricinus communis L. and Solanum mauritianum Scop.), and three native cicada species (Capicada decora Germar, Platypleura deusta Thun. and P. capensis L.) in South Africa, Lesotho and Swaziland. These models were quantitatively compared with models produced by means of the algorithm used in the BIOCLIM modelling package, which is referred to as a crisp envelope model (the CEM design). The average performance of models of the FEM design was consistently higher than those of the CEM design. There were significant differences in model performance among species but there was no significant interaction between model design and species. The average maximum kappa value ranged from 0.70 to 0.90 for FEM design and from 0.57 to 0.89 for the CEM design, which can be described as 'good' to 'excellent' using published ranges of agreement for the kappa statistic. This technique can be used to predict species' potential distributions that could be used for identifying regions at risk from invasion by alien species. These predictions could also be used in conservation planning in the case of native species.
Simple interval estimate methods for proportions exhibit poor coverage and can produce evidently inappropriate intervals. Criteria appropriate to the evaluation of various proposed methods include: closeness of the achieved coverage probability to its nominal value; whether intervals are located too close to or too distant from the middle of the scale; expected interval width; avoidance of aberrations such as limits outside [0,1] or zero width intervals; and ease of use, whether by tables, software or formulae. Seven methods for the single proportion are evaluated on 96,000 parameter space points. Intervals based on tail areas and the simpler score methods are recommended for use. In each case, methods are available that aim to align either the minimum or the mean coverage with the nominal 1 - α.
Ecological response surfaces are nonlinear functions describing the way in which the abundances of taxa depend on the joint effects of = or >2 environmental variables. Continental-scale patterns in the relative abundances of plant taxa are dominated by the effects of macroclimate on the competive balance among taxa. Pollen analyses record such regional variations for major vegetation components. Empirical ecological response surfaces were derived from high-resolution climate models to yield testable reconstructions of vegetation in E North America. Response surface analysis consists of a remapping of abundance patterns from geographic space into climate space, and complements efforts to explain distributions in terms of biological processes. The surfaces focus attention on the climatic location of range limits and optima, and on less obvious phenomena such as the spatial pattern in the relative sensitivity of different taxa to spatial variation in the climatic variables. Such response surfaces may be coupled to palaeoclimatic simulations from high-resolution climate models to yield testable reconstructions of vegetational history.-from Authors
A model to predict global patterns in vegetation physiognomy was developed from physiological considerations influencing the distributions of different functional types of plant. Primary driving variables are mean coldest-month temperature, annual accumulated temperature over 5-degrees-C, and a drought index incorporating the seasonality of precipitation and the available water capacity of the soil. The model predicts which plant types can occur in a given environment, and selects the potentially dominant types from among them. Biomes arise as combinations of dominant types. Global environmental data were supplied as monthly means of temperature, precipitation and sunshine (interpolated to a global 0.5-degrees grid, with a lapse-rate correction) and soil texture class. The resulting predictions of global vegetation patterns were in good agreement with the mapped distribution of actual ecosystem complexes (Olson, J.S., Watts, J.A. & Allison, L.J. (1983) ORNL-5862, Oak Ridge Nat. Lab., 164 pp.), except where intensive agriculture has obliterated the natural patterns. The model will help in assessing impacts of future climate changes on potential natural vegetation patterns, land-surface characteristics and terrestrial carbon storage, and in analysis of the effects of past climate change on these variables.
The number of studies dealing with plant invasions is increasing rapidly, but the accumulating body of knowledge has unfortunately also spawned increasing confusion about terminology. Invasions are a global phenomenon and comparison of geographically distant regions and their introduced biota is a crucially important methodological approach for elucidation of the determinants of invasiveness and invasibility. Comparative studies of alien floras provide substantial new insights to our understanding of general patterns of plant invasions. Such studies, using information in previously published floras and checklists, are fundamentally dependent on the quality of the assessment of particular species with respect to their taxonomic identity, time of immigration and invasion status. Three crucial decisions should be made when defining the status of a plant species in a given region: (1) whether the taxon is native or alien to that region (origin status); (2) what is its position in the invasion process, i.e., when was it introduced (residence status); and (3) what is the degree of its naturalization and possible invasion (invasion status). Standard floras differ hugely in their treatment of non-native species and those with appropriate categorization of alien species according to their status are rather rare. The present paper suggests definitions of terms associated with plant invasions and places these into the context of floras. Recommendations are outlined on how to deal with the issue of plant invasions in standard floras with the aim of contributing to a better understanding between taxonomists and ecologists and allowing more detailed comparative analyses of alien floras of various regions of the world.
Cette étude explore les patrons géographiques de la richesse en espèces chez les plantes exotiques de l'Afrique du Sud au sein de zones ayant une superficie approximative de 675 km2 (25 × 27 km). Nous avons tenu compte de toutes les espèces exotiques pour lesquelles nous avions une mention et d'un sous-ensemble de celles-ci, soit les espèces qui envahissent la végétation naturelle et semi-naturelle. Nous avons utilisé comme principale source d'informations une banque de données nationale constituée à l'aide de spécimens d'herbier. Les données spécifiques aux espèces exotiques envahissantes proviennent d'un projet d'atlas national. Nous avons d'abord évalué l'importance de la disponibilité en énergie et l'hétérogénéité de l'habitat en tant qu'indicateurs de la richesse des espèces indigènes, exotiques et envahissantes. Les modèles de régression linéaire montrent que la richesse en espèces des trois groupes de plantes est expliquée par les mêmes variables. Les deux groupes de variables les plus importants sont les facteurs climatiques et le relief. Nous avons également examiné le role des espèces indigènes, de plusieurs variables environnementales et d'autres variables associées aux activités humaines pour expliquer la richesse des espèces exotiques et envahissantes. Les résultats révèlent une interaction entre les caractéristiques naturelles et les variables qui quantifient l'importance des activités humaines. Lorsque la richesse des espèces indigènes est ignorée, les variables associées aux activités humaines sont plus fortement corrélées à la richesse des espèces exotiques qu'avec celle des espèces envahissantes. Le nombre d'espèces exotiques et d'espèces envahissantes au sein de chaque zone de 675 km2 est corrélé de façon significative avec la richesse des espèces indigènes, un phénomène qui a été observé ailleurs dans le monde. L'analyse des résidus des valeurs observées et des valeurs prédites montre que les patrons diffèrent toutefois selon les biomes. Les résultats peuvent servir à planifier des politiques d'intervention à long terme, à l'échelle nationale. Ils suggèrent que les secteurs riches en espèces indigènes seront plus susceptibles d'être colonisés de façon soutenue par des plantes exotiques envahissantes et que des mesures d'atténuation devront être prises pour en diminuer les impacts.
Homoclime analysis of three weed species of potential significance to agriculture in New Zealand was undertaken. Using the Bio-climate Prediction System computer program (BIOCLIM), climatically suitable regions in New Zealand were estimated for Homeria flaccida Sweet, Chondrilla juncea L. and Emex australis Steinh., on the basis of their respective distributions in Australia. These estimates indicated that the current eradication campaign for Homeria is warranted, owing to the existence of extensive areas with a suitable climate on both of New Zealand's main islands. For Homeria, most of the known occurrences fell within regions predicted to be climatically suitable. For Chondrilla, only very small areas were predicted to be climatically suitable, due to the generally low temperatures that prevail during its reproductive period. This suggests that the designation of Chondrilla as a quarantine pest may be unwarranted. Much of the land in the interior of the North Island was estimated to be climatically suitable for Emex. However, invasion has not occurred, despite the presence of this weed in New Zealand for over 100 years. The failure of Emex to invade perennial pastures is probably a result of its poor competitiveness, since climatic and edaphic characteristics appear to be suitable over large areas. It is concluded that homoclime analysis can be used to identify regions at risk of invasion by a species which has been weedy elsewhere, when potentially modifying factors such as soils, land use/management practices and competitive interactions are taken into account.
We summarize information on naturalized and invasive conifers (class Pinopsida) worldwide (data from 40 countries, some with remote states/territories), and contrast these findings with patterns for other gymnosperms (classes Cycadopsida, Gnetopsida and Ginkgoopsida) and for woody angiosperms. Eighty conifer taxa (79 species and one hybrid; 13% of species) are known to be naturalized, and 36 species (6%) are ‘invasive’. This categorization is based on objective and conservative criteria relating to consistency of reproduction, distance of spread from founders, and degree of reliance on propagules from the founder population for persistence in areas well outside the natural range of species. Twenty-eight of the known invasive conifers belong to one family (Pinaceae) and 21 of these are in one genus (Pinus). The Cupressaceae (including Taxodiaceae) has six known invasive species (4%) in four genera, but the other four conifer families have none. There are also no known invasive species in classes Cycadopsida, Gnetopsida or Ginkgoopsida. No angiosperm family comprising predominantly trees and shrubs has proportionally as many invasive species as the Pinaceae.
In the northern Mediterranean Basin, agricultural land abandonment over the last century has resulted in increasing frequencies of very large, intense fires. In Catalonia (NE Spain) some fires have been locally associated with the expansion of the large, evergreen, resprouting tussock grass Ampelodesmos mauritanica. We tested the hypothesis of a positive feedback between the abundance of A. mauritanica and changing fire regimes.
We used permanent plots distributed across a natural gradient of density of A. mauritanica in the Garraf Natural Park near Barcelona. Total aboveground biomass nearly doubled from plots with low to high density through a combination of A. mauritanica replacing the biomass of other components of the community (predominantly native shrubs), and its absolute standing biomass increasing. The quantity of litter also increased. This increase in fuel load and changes in community functional composition resulted from the simultaneous decrease in shrub productivity and an increase in litter accumulation. Litter accumulation was the consequence of A. mauritanica litter decomposing 30% more slowly than that of shrubs. Under standardized conditions, A. mauritanica and its litter were considerably more flammable than any of the shrub species. This resulted in a more than 40-fold increase in calculated plot flammability from low-to-high-density plots.
Feedbacks, at the landscape scale, were then analysed using the landscape simulation platform LAMOS. Invasion success and contribution to community biomass of A. mauritanica increased with decreasing fire return intervals. Total area burnt in the landscape during each fire year was positively and exponentially related to the total biomass of A. mauritanica. Simulations showed that landscapes can abruptly switch from regimes of small localized to extensive fires as a result of the spread of A. mauritanica. Therefore, increases in fires under climate change represent threats not only through their direct impacts on ecosystems, but also by promoting invaders such as A. mauritanica, which have the potential to induce powerful feedforward processes and, thereby, fundamental changes to ecosystems.
Models based on generalized plant physiological theory represent a promising approach for describing vegetation responses to environmental drivers on large scales but must be tested for their ability to reproduce features of real vegetation. We tested the capability of a generalized vegetation model (LPJ-GUESS) to simulate vegetation structural and com-positional dynamics under various disturbance regimes at the transition between prairie, northern hardwoods, and boreal forest in the Great Lakes region of the United States. LPJ-GUESS combines detailed representations of population dynamics as commonly used in forest gap models with the same mechanistic representations of plant physiological processes as adopted by a dynamic global vegetation model (the Lund-Potsdam-Jena [LPJ] model), which has been validated from the stand to the global scale. The model does not require site-specific calibration. The required input data are information on climate, at-mospheric CO 2 concentration, and soil texture class, as well as information on generally recognized species traits (broad-leaved vs. needle-leaved, general climatic range, two fire-resistance classes, shade-tolerance class, and maximum longevity). Model predictions correspond closely to observed patterns of vegetation dynamics and standing biomass at an old-growth eastern hemlock (Tsuga canadensis)/hardwood forest (Sylvania Wilderness, Michigan), an old-growth forest remnant from the ''Great Lakes Pines Forest'' (Itasca State Park, Minnesota), and a presettlement savanna (Cedar Creek Natural History Area, Minnesota). At all three sites, disturbance (wind or fire) strongly controls species composition and stand biomass. The model could be used to simulate vegetation dynamics on a regional basis or under past or future climates and atmospheric CO 2 levels, without a need for reparameterization.
We investigated factors hypothesized to influence introduction success and subsequent geographical range size in 52 species of bird that have been introduced to mainland Australia.
The 19 successful species had been introduced more times, at more sites and in greater overall numbers. Relative to failed species, successfully introduced species also had a greater area of climatically suitable habitat available in Australia, a larger overseas range size and were more likely to have been introduced successfully outside Australia. After controlling for phylogeny these relationships held, except that with overseas range size and, in addition, larger‐bodied species had a higher probability of introduction success. There was also a marked taxonomic bias: gamebirds had a much lower probability of success than other species. A model including five of these variables explained perfectly the patterns in introduction success across‐species.
Of the successful species, those with larger geographical ranges in Australia had a greater area of climatically suitable habitat, traits associated with a faster population growth rate (small body size, short incubation period and more broods per season) and a larger overseas range size. The relationships between range size in Australia, the extent of climatically suitable habitat and overseas range size held after controlling for phylogeny.
We discuss the probable causes underlying these relationships and why, in retrospect, the outcome of bird introductions to Australia are highly predictable.
Much confusion exists in the English-language literature on plant invasions concerning the terms ‘naturalized’ and ‘invasive’ and their associated concepts. Several authors have used these terms in proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology.
Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction (approximate scales: > 100 m over < 50 years for taxa spreading by seeds and other propagules; > 6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers.
We propose that the term ‘invasive’ should be used without any inference to environmental or economic impact. Terms like ‘pests’ and ‘weeds’ are suitable labels for the 50–80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed ‘transformers’.
Anthropogenic changes in the global climate are shifting the potential ranges of many plant species.
Changing climates will allow some species the opportunity to expand their range, others may experience a contraction in their potential range, while the current and future ranges of some species may not overlap. Our capacity to generalize about the threat these range shifts pose to plant diversity is limited by many sources of uncertainty.
In this paper we summarize sources of uncertainty for migration forecasts and suggest a research protocol for making forecasts in the context of uncertainty.
Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well-known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high-risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility.
The homoclime approach has been used to estimate the potential distributions of the exotic goldenrods Solidago altissima, S. gigantea, and S. graminifolia in Europe. These three rhizomatous perennial plants were introduced as ornamentals about 250 years ago. Whereas S. altissima and S. gigantea have become widespread and serious invaders of abandoned fields, forest edges, and river banks, S. graminifolia is still confined to a few sites in Europe. Climatic profiles of their native ranges have been established for each species based on nine parameters from stations throughout their American ranges. I determined potential distributions for each species by mapping European stations that match the climatic profiles. The potential distributions of all three species are substantially larger than their current distributions in Europe. Areas not yet colonized but predicted to be climatically suitable included parts of southern and southeastern Europe, Scandinavia, and the Middle East. Among the three species, the potential range of S. altissima was largest in its latitudinal extent. The discrepancy between current and potential range was highest in S. graminifolia because of its restricted distribution. My results strongly suggest that the spread of S. altissima and S. gigantea has not yet reached its limits and that their range expansion will continue. Large parts of Europe were estimated to be climatically suitable to S. graminifolia, but invasion has not yet occurred. This species is either in lag phase or its spread is limited by factors other than climate.
Successful management of invasive weeds will require active attempts to prevent new introductions, vigilant detection of nascent populations and persistent efforts to eradicate the worst invaders. To achieve these objectives, invasion ecology offers five groups of complementary approaches. (i) Stochastic approaches allow probabilistic predictions about potential invaders based on initial population size, residence time and number of introduction attempts. (ii) Empirical taxon-specific approaches are based on previously documented invasions of particular taxa. (iii) Evaluations of the biological characters of non-invasive taxa and successful invaders give rise either to general or to habitat-specific screening procedures. (iv) Evaluation of environmental compatibility helps to predict whether a particular plant taxon can invade specific habitats. (v) Experimental approaches attempt to tease apart intrinsic and extrinsic factors underlying invasion success. An emerging theory of plant invasiveness based on biological characters has resulted in several rather robust predictions which are presented in this paper.
Most, if not all, alien plant species of the family Acanthaceae (acanths) found in tropical islands were intentionally introduced as garden ornamentals, because of their showy coloured flowers, bracts or leaves. Some have ‘escaped’ gardens and have naturalized in human-disturbed areas as weeds, adventives, or ruderal species. A few species have successfully invaded secondary and relatively undisturbed native wet forests. This paper reviews the naturalized alien acanths in tropical islands, and focuses on the currently invasive and potentially invasive species. This study is based on recent (1994–2004) botanical surveys and field observations conducted in several tropical oceanic islands of the Pacific and Indian Oceans, and on bibliographical searches of other tropical islands and countries. A total of 52 acanth species are naturalized in the Indo-Pacific islands; 26 of them are native to Asia, 18 to tropical America, and only 8 to Africa. The number of naturalized acanths in selected tropical oceanic and continental islands varied from 7 to 25 species and the rate of naturalized acanths (number of naturalized species/number of introduced species) from 27% to 62%. We recorded eight major invasive species: the erect herbs or shrubs Justicia carnea, Odontonema strictum, Phlogacanthus turgidus, Sanchezia speciosa and Strobilanthes hamiltonianus form dense monospecific thickets in the understorey of wet forests; the woody vine Thunbergia grandiflora smothers native trees; the creeping herb Hemigraphis alternata forms dense carpets that totally cover the ground; and the herb Ruellia brevifolia colonizes the understorey of closed-canopy wet forest. We also discuss eight potentially or incipient invasive acanths which are subspontaneous or sparingly naturalized, but which are not yet considered invasive. Most of the currently invasive acanths are sterile, the lack of fruit production being explained by the absence of pollinators and/or to their particular floral structure and reproduction modes. They reproduce vegetatively by stem fragmentation or by root suckers, and their range expansion is thus relatively slow. Their success may be attributed to their long (50–100 years) residence times, and long-distance dispersal by humans. Many potentially invasive acanths are newly introduced ornamentals that produce seeds, thus constituting potentially greater threats. The Acanthaceae is not yet recognized as an ‘aggressive’ plant family (e.g. compared to the Fabaceae, Melastomataceae, Poaceae, or Rosaceae). It is, however, one of the most popular ornamental families in the Tropics, and should receive more attention because of the increasing number of current and incipient invasive species found in tropical islands.
Biotic resistance describes the ability of resident species in a community to reduce the success of exotic invasions. Although resistance is a well-accepted phenomenon, less clear are the processes that contribute most to it, and whether those processes are strong enough to completely repel invaders. Current perceptions of strong, competition-driven biotic resistance stem from classic ecological theory, Elton's formulation of ecological resistance, and the general acceptance of the enemies-release hypothesis. We conducted a meta-analysis of the plant invasions literature to quantify the contribution of resident competitors, diversity, herbivores and soil fungal communities to biotic resistance. Results indicated large negative effects of all factors except fungal communities on invader establishment and performance. Contrary to predictions derived from the natural enemies hypothesis, resident herbivores reduced invasion success as effectively as resident competitors. Although biotic resistance significantly reduced the establishment of individual invaders, we found little evidence that species interactions completely repelled invasions. We conclude that ecological interactions rarely enable communities to resist invasion, but instead constrain the abundance of invasive species once they have successfully established.
To assess the validity of previously developed risk assessment schemes in the conditions of Central Europe, we tested (1) Australian weed risk assessment scheme (WRA; Pheloung et al. 1999); (2) WRA with additional analysis by Daehler et al. (2004); and (3) decision tree scheme of Reichard and Hamilton (1997) developed in North America, on a data set of 180 alien woody species commonly planted in the Czech Republic. This list included 17 invasive species, 9 naturalized but non-invasive, 31 casual aliens, and 123 species not reported to escape from cultivation. The WRA model with additional analysis provided best results, rejecting 100% of invasive species, accepting 83.8% of non-invasive, and recommending further 13.0% for additional analysis. Overall accuracy of the WRA model with additional analysis was 85.5%, higher than that of the basic WRA scheme (67.9%) and the Reichard–Hamilton model (61.6%). Only the Reichard–Hamilton scheme accepted some invaders. The probability that an accepted species will become an invader was zero for both WRA models and 3.2% for the Reichard–Hamilton model. The probability that a rejected species would have been an invader was 77.3% for both WRA models and 24.0% for the Reichard–Hamilton model. It is concluded that the WRA model, especially with additional analysis, appears to be a promising template for building a widely applicable system for screening out invasive plant introductions.
Ecosystems of Hawaii and other Pacific Islands have been greatly affected by invasive pest plants, and ongoing, deliberate plant introductions make it likely that additional pest plants will become established. We tested the ability of a modified version of the Australian and New Zealand weed risk-assessment system to identify pest plants in Hawaii and other Pacific Islands. We used information taken from outside Hawaii to predict the behavior—“pest” or “not a pest”—of almost 200 plant species introduced to Hawaii and other Pacific Islands. The screening system initially recommended further evaluation of 24% of these species, but an additional secondary screening was applied to this group, thereby reducing the rate of indecision to only 8%. To independently test the accuracy of the screening system, we compared its decisions—pest or not a pest—to opinions of 25 expert botanists and weed scientists who had substantial field experience in Hawaii or other Pacific Islands. We asked the experts to rate each species as “major pest,”“minor pest,” or “not a pest” in native or managed ecosystems. The screening system correctly identified 95% of major pests and 85% of nonpests. Among minor pests identified by the experts, 33% were classified as nonpests by the screening system. Use of the screening system to assess proposed plant introductions to Hawaii or other Pacific Islands and to identify high-risk species used in horticulture and forestry would greatly reduce future pest-plant problems and allow entry of most nonpests. The screening process is objective, rapid, and cost-efficient. With minor modifications, it is likely to be useful in many parts of the world.
Screening systems for predicting invasive plants have been independently developed for the non-indigenous floras of North
America, the South African fynbos, and Australia. To evaluate the performance of these screening systems outside the regions
for which they were developed, we tested them for the non-indigenous flora of the Hawaiian Islands. When known invasive plant
species in the Hawaiian Islands were evaluated using the North American and Australian systems, 82% and 93% of the species
were predicted to be invasive, respectively, and the remainder were classified as requiring further study. The South African
fynbos system correctly predicted only 60% of the invasive species in the Hawaiian Islands. All three screening systems correctly
classified a majority of the non-invaders as non-invasive. The Australian system has several advantages over the other systems,
including the highest level of correct identification of invaders (>90%), ability to evaluate non-woody plants, and ability
to evaluate a species even when the answers to some questions are unknown. Nevertheless, with the Australian system, a large
fraction of species known not to be invasive were recommended for further study before importing, so there remains room for
improvement in identifying non-invasive species. Based on our results for the Hawaiian Islands and a previous evaluation in
New Zealand, the Australian system appears to be a promising template for building a globally applicable system for screening
out invasive plant introductions.
In the last two decades, interest in species distribution models (SDMs) of plants and animals has grown dramatically. Recent advances in SDMs allow us to potentially forecast anthropogenic effects on patterns of biodiversity at different spatial scales. However, some limitations still preclude the use of SDMs in many theoretical and practical applications. Here, we provide an overview of recent advances in this field, discuss the ecological principles and assumptions underpinning SDMs, and highlight critical limitations and decisions inherent in the construction and evaluation of SDMs. Particular emphasis is given to the use of SDMs for the assessment of climate change impacts and conservation management issues. We suggest new avenues for incorporating species migration, population dynamics, biotic interactions and community ecology into SDMs at multiple spatial scales. Addressing all these issues requires a better integration of SDMs with ecological theory.
Disturbance and land transformation seem to enhance the ability of exotic species to invade, possibly due to increased resource levels and greater immigration potential from surrounding disturbed areas. To investigate the role disturbance may play in enhancing exotic species invasion, we used retrospective analysis to discriminate the characters associated with naturalized and non-naturalized exotic woody plants in New Hampshire utilizing the biological information contained in the US Department of Agriculture (USDA) PLANTS database and selected other sources. Exotic plants were partitioned into two groups: those known to have self-sustaining populations and those that did not display self-sustaining populations. To predict membership into these groups, we used stepwise logistic regression. Variables were screened for correlation coefficients higher than 0.5. Model development was constrained using Akaike’s information criteria with the correction factor for sample size. The 11th model step containing 11 characters was selected and it differed significantly from the constant-only model (χ2=66.383, P<0.001). Exotic species were correctly classified into the known non-naturalized or naturalized categories in 90% of the cases. The resulting model could be used to reliably screen novel woody plant introductions. Additionally, we provide a framework for preliminarily assessing the importance of different factors in encouraging woody plant invasion in the northeastern US.
An important statistical development of the last 30 years has been the advance in regression analysis provided by generalized linear models (GLMs) and generalized additive models (GAMs). Here we introduce a series of papers prepared within the framework of an international workshop entitled: Advances in GLMs/GAMs modeling: from species distribution to environmental management, held in Riederalp, Switzerland, 6–11 August 2001.We first discuss some general uses of statistical models in ecology, as well as provide a short review of several key examples of the use of GLMs and GAMs in ecological modeling efforts. We next present an overview of GLMs and GAMs, and discuss some of their related statistics used for predictor selection, model diagnostics, and evaluation. Included is a discussion of several new approaches applicable to GLMs and GAMs, such as ridge regression, an alternative to stepwise selection of predictors, and methods for the identification of interactions by a combined use of regression trees and several other approaches. We close with an overview of the papers and how we feel they advance our understanding of their application to ecological modeling.
We present generalized regression analysis and spatial prediction (GRASP) conceptually as a method for producing spatial predictions using statistical models, and introduce and demonstrate a specific implementation in Splus that facilitates the process. We put forward GRASP as a new name encapsulating an existing concept that aims at making spatial predictions using generalized regression analysis. Regression modeling is used to establish relationships between a response variable and a set of spatial predictors. The regression relationships are then used to make spatial predictions of the response. The GRASP process requires point measurements of the response, as well as regional coverages of predictor variables that are statistically (and preferably causally) important in determining the patterns of the response. This approach to spatial prediction is becoming more commonplace, and it is useful to define it as a general concept. For instance, GRASP could use a survey of the abundance of a species (the response), and existing spatial coverages of environmental (e.g. climate, landform) variables (the predictors) for a region. A multiple regression can be used to establish the statistical relationship between the species abundance and the environmental variables. These regression relationships can then be used to predict the species abundance from the environmental surfaces. This process defines relationships in environmental space and uses these relationships to predict in geographic space. We introduce GRASP (the implementation) as an interface and collection of functions in Splus designed to facilitate modern regression analysis and the use of these regressions for making spatial predictions. GRASP standardizes the modeling process and makes it more reproducible and less subjective, while preserving analysis flexibility. The set of functions provides a toolbox that allows quick and easy data checking, model building and evaluation, and calculation of predictions. The current version uses generalized additive models (GAMs), a modern non-parametric regression technique the advantages of which are discussed. We demonstrate the use of the GRASP implementation to model and predict the natural distributions of two components of New Zealand fern biodiversity: (1) the natural distribution of an icon species, silver fern (Cyathea dealbata); and (2) the natural pattern of total fern species richness. Key steps are demonstrated, including data preparation, options setting, data exploration, model building, model validation and interpretation, and spatial prediction.
Prediction of the potential for plant species to invade new ranges has long attracted the attention of ecologists motivated by both fundamental and practical considerations. Consequently, a conceptually diverse array of correlative and experimental approaches have been developed to predict the identity and fate of future invaders. The most straightforward approach has long involved simply compiling lists of species known to be aggressive either in their native range or a new range. Although these lists can be encyclopedic, they often fail to include species that have yet to become aggressive anywhere. As a result, much effort has been devoted instead to searching for commonality in the ecological traits of invading species as a predictive tool. Success in using such distillations is hampered by the emphasis on the traits of ruderals, despite the ability of non-ruderals to become naturalized, and the frequent inability to decipher which traits contribute to a species' naturalization from those that are merely coincidental with naturalization. The intuitively-appealing approach of identifying a region's future invaders among species that are aggressive in regions with a similar climate (‘climatic-matching’) fails to account for the often quite different biotic restrictions among regions with similar climates. A fourth correlative tool, predictions of an alien species' future distribution and prominence based on its initial rate of spread, is handicapped by our lack of comprehensive knowledge on the areal patterns and temporal course that invasions may follow. In contrast to these correlative tools, prediction has also been sought by determining the constraints of the physical environment on alien species in controlled-growth facilities and glasshouses. Although such facilities certainly provide instructive results, potential interactions between and among factors, especially biotic factors, are difficult to simulate. Three other experimental approaches offer a higher rate of prediction: simultaneous field comparisons between congeners (e.g. one naturalized, one native), and following the fate of a species deliberately sown in a natural community beyond its current range, with or without environmental manipulation. Evaluation of the efficacy of these last three approaches awaits their wider application. Although the experimental approaches hold greater promise, none is a panacea. Prediction will be the highest when several approaches are combined simultaneously (e.g. manipulating the environment for congeners in the field).
New plant taxa from around the world continue to be imported into Australia and New Zealand. Many of these taxa have the potential to become agricultural or environmental weeds and this risk needs to be assessed before allowing their entry. A weed risk assessment system is described that uses information on a taxon's current weed status in other parts of the world, climate and environmental preferences, and biological attributes. The system is designed to be operated by quarantine personnel via a user-friendly computer interface.The model was tested against experts' scores for weediness for 370 taxa present in Australia, representing both weeds and useful taxa from agriculture, the environment, and other sectors. The model was judged on its ability to correctly ‘reject’ weeds, ‘accept’ non-weeds, and generate a low proportion of taxa which could not be decisively categorised, termed ‘evaluate’. More than 70% of the taxa were rejected or accepted. All taxa classified as serious weeds, and most minor weeds, were rejected or required further evaluation, while only 7% of non-weeds were rejected. The model was modified to New Zealand conditions and evaluated against the opinions of several groups of experts and against economic measures. The model produced a weediness score very similar to the mean of the experts scores. The latter were highly variable: agriculturalists tended to accept known weeds, conservationists tended to reject most adventive taxa, and only botanists produced scores similar to the model. The model scores also tended to be independent of economic value as measured in this study. The model could be adapted for use as a screening tool in any region of the world.
The development and application of an expert system is described for screening alien woody plants for their invasive potential in South African fynbos. The system is proposed for use by potential introducers to demonstrate low invasive risk before importing woody alien species for cultivation. Rules for the system were derived from empirical evidence by quantifying invasion windows and barriers that have limited the set of widespread woody invaders (trees and shrubs) in fynbos to fewer than 20, out of several hundred introduced species. The system first compares broad-scale environmental conditions (climate and soil) between the home environment of a species and fynbos. Features of the plant in its home environment (basic life history traits, population characteristics, regeneration biology, habitat preferences) are then assessed. Finally, an assessment is made of life history adaptations to the prevailing fire regime in fynbos (juvenile period, fire-survival capacity of adult plants, seed bank longevity). The reasoning is explicit and the steps leading to a conclusion (high risk/low risk) can be retraced.Besides the obvious application in identifying species with a high risk of invading, the system has considerable potential for modelling, and for teaching the concepts of biological invasions. The rules provide an explicit conceptualization of invasion processes in fynbos and identify multiple paths to invasive success (not all of which have been realized yet). The system can therefore be used in planning control operations (for optimal allocation of control effort to critical stages in invasion), and for predicting the outcome of changes (e.g. in fire frequency) on the dimensions of invasion windows, and for assessing what changes are needed to prevent or reduce the extent of invasion by a given taxon.Application of the system is demonstrated on Pinus and Banksia taxa and a selection of species from Californian chaparral.
Natural areas are becoming increasingly fragmented and embedded in an urban matrix. Natural and semi-natural areas at the urban/wildland interface are threatened by a variety of ‘edge effects’, and are especially vulnerable to invasion by introduced plants, with suburban gardens acting as significant sources of alien propagules. Urban/wildland interfaces also provide access for humans, leading to various types of disturbance. Alien plant invasions are one of the biggest threats facing remaining natural areas on the Cape Peninsula, South Africa. The area provides an ideal opportunity to study the dynamics of invasions at the urban/wildland interface, since the largest natural area, the Table Mountain National Park (TMNP), is surrounded by the city of Cape Town. We explored invasion patterns in Newlands Forest (a small section of the TMNP) and detailed the roles of habitat features and distance from putative source populations in three main habitat types: natural Afromontane forest, riverine woodland habitats, and plantations of exotic pines (Pinus radiata and P. pinaster). We also examined the role of disturbance in driving invasions in two of these habitat types (Afromontane forest and pine plantations). We hypothesized that alien richness and alien stem density would decrease with distance from the urban/wildland interface, and that alien richness and alien stem density would increase with increasing levels of human disturbance.
The Rain Use Efficiency (RUE) factor is the quotient of annual primary production by annual rainfall, ie the number of kilograms aerial dry matter phytomass produced over 1 ha in 1 year per millimetre of total rain fallen. It may be expressed in Above Ground Net Primary Production, in Maximum Standing Crop (for therophytic or ephemeroid vegetation types), in Herbage Yield or in any other production measurement system, as long as the reference system is clearly indicated. All other conditions remaining equal, RUE tends to decrease when aridity increases together with the rate of useful rains, and as potential evapotranspiration increases.-from Author