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Richardson, D. M. and P. Pysek. Plant invasions: merging the concepts of species invasiveness and community invasibility. Progress in Physical Geography
Abstract
This paper considers key issues in plant invasion ecology, where findings published since 1990 have significantly improved our understanding of many aspects of invasions. The review focuses on vascular plants invading natural and semi-natural ecosystems, and on fundamental ecological issues relating to species invasiveness and community invasibility. Three big questions addressed by the SCOPE programme in the 1980s (which species invade; which habitats are invaded; and how can we manage invasions?) still underpin most work in invasion ecology. Some organizing and unifying themes in the field are organism-focused and relate to species invasiveness (the tens rule; the concept of residence time; taxonomic patterns and Darwin's naturalization hypothesis; issues of phenotypic plasticity and rapid evolutionary change, including evolution of increased competitive ability hypothesis; the role of long-distance dispersal). Others are ecosystem-centred and deal with determinants of the invasibility of communities, habitats and regions (levels of invasion, invasibility and propagule pressure; the biotic resistance hypothesis and the links between diversity and invasibility; synergisms, mutualisms, and invasional meltdown). Some theories have taken an overarching approach to plant invasions by integrating the concepts of species invasiveness and community invasibility (a theory of seed plant invasiveness; fluctuating resources theory of invasibility). Concepts, hypotheses and theories reviewed here can be linked to the naturalization-invasion continuum concept, which relates invasion processes with a sequence of environmental and biotic barriers that an introduced species must negotiate to become casual, naturalized and invasive. New research tools and improved research links between invasion ecology and succession ecology, community ecology, conservation biology and weed science, respectively, have strengthened the conceptual pillars of invasion ecology.
... Given the global priority of managing invasive alien species for biodiversity conservation, research has focused on identifying the traits that enhance invasiveness and assessing which habitats are most susceptible to 2 invasion (Pyšek et al., 1995;Alpert et al., 2000;Richardson and Pyšek, 2006;Pyšek et al., 2012). Plant productivity, influenced by competitive abilities and reproductive strategies, is particularly sensitive to environmental conditions (Daehler, 2003;Medina-Villar, 2020). ...
... Despite numerous studies, the latest reviews highlight that identifying specific traits linked to invasiveness remains challenging (Alpert et al., 2000;Richardson and Pyšek, 2006;Pyšek et al., 2012). However, key parameters such as species' evolutionary background, community structure, propagule pressure, habitat disturbance, and environmental stress are linked to invasiveness (Higgins and Richardson, 1999;Alpert et al., 2000;Richardson and Pyšek, 2006;Pyšek et al., 2012). ...
... Despite numerous studies, the latest reviews highlight that identifying specific traits linked to invasiveness remains challenging (Alpert et al., 2000;Richardson and Pyšek, 2006;Pyšek et al., 2012). However, key parameters such as species' evolutionary background, community structure, propagule pressure, habitat disturbance, and environmental stress are linked to invasiveness (Higgins and Richardson, 1999;Alpert et al., 2000;Richardson and Pyšek, 2006;Pyšek et al., 2012). ...
The negative impact of invasive alien species on biodiversity, agriculture, ecosystem services, and human well-being is a significant concern for scientists. Despite extensive research in the past decade to understand their effects on native communities and ecosystems, predicting and managing future invasions remains challenging. Humulus scandens, a species native to Asia, was introduced to Europe in 1880 for ornamental purposes. This vigorous climbing vine thrives in wetlands, riparian habitats (especially river and stream sides), and ruderal habitats (roadsides, wastelands, abandoned, and disturbed areas). Our research aimed to investigate the vegetative body structure of H. scandens to understand its high resilience in Romanian habitats. The structural characterization of the vegetative organs involved detailed microscopic examination of the coloured cross-sections. The results revealed a well-developed secondary structure of the root and stem, granting robustness and resistance to the plant, favouring it in competition with other species for environmental resources.
... An invasive alien plant is a naturalized species whose progeny reproduce at long distances from the parent plant and can therefore spread over large areas of the landscape (Richardson et al., 2000). This means that for a species to be a successful invader, it must not only be transported and introduced into a recipient community, but also have the ability to establish and spread (Richardson et al., 2000;Richardson & Pyšek, 2006). The level of invasion of an ecosystem is the result of three main interacting factors: (1) the effort of introduction (i.e., propagule pressure), (2) the capacity of a species to invade (i.e., invasiveness), (3) and the susceptibility of the recipient community to be invaded (i.e., invasibility; Lonsdale, 1999;Richardson & Pyšek, 2006;Catford et al., 2009). ...
... This means that for a species to be a successful invader, it must not only be transported and introduced into a recipient community, but also have the ability to establish and spread (Richardson et al., 2000;Richardson & Pyšek, 2006). The level of invasion of an ecosystem is the result of three main interacting factors: (1) the effort of introduction (i.e., propagule pressure), (2) the capacity of a species to invade (i.e., invasiveness), (3) and the susceptibility of the recipient community to be invaded (i.e., invasibility; Lonsdale, 1999;Richardson & Pyšek, 2006;Catford et al., 2009). These factors can control different barriers (i.e., survival, growth, reproduction and dispersal) that affect the progression of invasion steps (i.e., transport, introduction, establishment and spread) along the invasion process (Richardson & Pyšek, 2006;Theoharides & Dukes, 2007;Catford et al., 2009;Blackburn et al., 2011). ...
... The level of invasion of an ecosystem is the result of three main interacting factors: (1) the effort of introduction (i.e., propagule pressure), (2) the capacity of a species to invade (i.e., invasiveness), (3) and the susceptibility of the recipient community to be invaded (i.e., invasibility; Lonsdale, 1999;Richardson & Pyšek, 2006;Catford et al., 2009). These factors can control different barriers (i.e., survival, growth, reproduction and dispersal) that affect the progression of invasion steps (i.e., transport, introduction, establishment and spread) along the invasion process (Richardson & Pyšek, 2006;Theoharides & Dukes, 2007;Catford et al., 2009;Blackburn et al., 2011). ...
Question
Understanding the patterns of alien plant invasions and their underlying drivers is a key step in conserving the remaining native grasslands of Uruguay. We addressed the level of invasion by considering the four invasive alien plants of these ecosystems, Cynodon dactylon , Eragrostis plana , Senecio madagascariensis and Ulex europaeus , throughout the country.
Location
Remnant native grasslands of Uruguay, constituting part of the Río de la Plata grasslands.
Methods
Extensive fieldwork was carried out over five years of data collection, including hierarchically randomized observations (around 2000) nested in 137 10 × 10‐km ² squares covering different geomorphological regions. For each invasive alien species, we constructed distribution maps to show their patterns; for the two most abundant, we fitted models to identify the main explanatory variables at different spatial scales.
Results
We found that 77% of the squares were invaded by at least one target species. The level of invasion varied between regions and target plants. The most abundant invasive alien species were Cynodon dactylon and Senecio madagascariensis; while Eragrostis plana and Ulex europaeus were scarce. Cynodon dactylon cover was related to a set of variables at different spatial scales, including climate, topography and several local community descriptors. Senecio madagascariensis cover was positively associated with grassland fragmentation and anthropic disturbance at the landscape, and a few local descriptors.
Conclusions
The large sampling effort at the country level, with a randomized design, allowed for a reliable assessment of the level of invasion of Uruguayan grasslands and its possible drivers. This is an important step in the design of policies to conserve Uruguay's remaining native grasslands. We suggest that the prevention should focus on the Basaltic Cuestas region, while control and containment should prioritize the eastern and south‐central parts of the country, focusing mainly on Cynodon dactylon management.
... The process of invasion has been considered a multistage process starting from the introduction of a non-native species to becoming an invasive species. Only a small fraction of introduced species become invasive (Richardson and Pyšek 2006;Blackburn et al. 2014). ...
... In the literature, several synonymous terms exist often leading to confusion, especially for readers who are new to the field of invasion ecology. Non-native plants are synonymous with alien plants or exotic plants and have been used interchangeably (Richardson and Pyšek 2006). ...
... Confusion may arise when these terms are employed informally. For example, often the term naturalized is used to refer to invasive species and vice-versa although the distinction between the different stages of the invasion process is desirable (Richardson and Pyšek 2006). For this manuscript, we will follow the definitions by Richardson et al. in 2000 since they have been widely accepted in invasion ecology (Meyerson and Mooney 2007;Blackburn et al. 2011;Van Kleunen et al. 2015;Ricciardi et al. 2017;Van Kleunenet al. 2018). ...
Biological invasion is the second most important threat to biodiversity and consequently is a cause of great concern for the ecology and economy of the invaded community. Documentation of invasive plants in a region is crucial as it provides the baseline information for future research and management activities. In this study, we have produced an annotated checklist of the invasive alien plants of Gorakhpur district in the Terai region of Eastern Uttar Pradesh based on field observation, existing literature, and herbarium consultation. A total 58 alien plants species are listed, belonging to 25 angiosperm families of which 15 alien species are invasive having high impact, 37 alien species are naturalized having moderate impact and 6 alien species are casual having low impact over ecological communities. All the invasive plants are not equally problematic and spread across the district while some of them viz. Ageratum houstonianum Mill., Alternanthera philoxeroides (Mart.) Abh., Chromolaena odorata (L.) R.M. King & H. Rob., Mesosphaerum suaveolens (L.) Kuntze., Mikania micrantha Kunth Nov., Parthenium hysterophorus L., Pontederia crassipes Mart., Antigonon leptopus Hook. & Arn., Lantana camara L., are spread in most parts of the district and they are capable of spreading into the protected areas of this region. The present study is based on firsthand field observations, and provides a detailed and recent checklist of invasive species of Gorakhpur district. Therefore, this information can help researchers and policymakers to develop effective management strategies.
... The position of alien species throughout the introduction-naturalization-invasion continuum is the primary issue that needs to be addressed in trait-based approaches (Blackburn et al. 2011). Invasive species, or alien species, which propagate over specific distances, may differ in certain aspects from non-invasive species, or foreign species that reproduce in the wild but do not spread quickly in the introduced region (Richardson and Pyšek 2006). The habitat context of invasions is a crucial topic that needs to be covered in the trait-based research of invasiveness. ...
... The functional traits of the local flora, where certain organisms might be more saturated than others, lead to an invasion's success. Accelerated phenotypic plasticity in specific traits has been the subject of previous attempts and broad analysis (Richardson and Pyšek 2006). These studies suggest that high phenotypic plasticity in present traits may play a role in promoting invasion success by enabling the expression of advantageous phenotypes in a variety of ecosystems (Matesanz et al. 2015). ...
Plant functional traits refer to physio-morpho-phenological qualities that indirectly impact fitness or performance by influencing the life history strategies of plants. Unfortunately, climate change increase stressors that are making plants less resilient. This changes the structure of forests and the ecosystem services they provide, which causes these traits to change over time. Functional traits have been widely used in two key areas of research; firstly, they are employed to describe how communities respond to environmental changes, and secondly, functional traits are used to analyze the impact of community shifts on processes of the ecosystem. The researchers can assess how these alterations influence the functioning of ecosystems by examining changes in traits within a community. Numerous methodologies have been elucidated in analyzing predetermined trait sets in relation to the environment. This chapter explores the diverse aspects of plant functional traits, emphasizing their role in shaping ecosystems and addressing the pressing challenges of our time. Through an integrative approach that combines ecological research, data synthesis, and technological advancements, this chapter aims to deepen our understanding of plant functional traits and their significance or implications for the sustainable management of natural resources. Hence, measuring and understanding traits enhance our comprehension of ecological processes, contributing to advancing conservation and restoration efforts.
... Our results indicate that plant interaction networks can affect a community's vulnerability to invasion by affecting the average growth rate of the resident community. As a slower average growth rate (productivity) of the resident community equates to a reduced competitive ability, this result is consistent with theory that shows that invasion can occur when the invader has a competitive advantage over resident species 5,6 . However, how plant interaction networks affected the average growth rate of the community, and thus invasibility, was not simply due to the presence/absence of negative or positive interactions. ...
... However, interestingly, our results provide a novel explanation for why the relationship between coexistence, diversity, productivity, and community invasibility can be complex, based on plant species interaction networks alone. Therefore, our results add to a growing body of literature that suggests that how diversity affects invasibility depends critically on the processes regulating diversity in resident communities 5,12,28,29 . ...
Understanding what makes a community vulnerable to invasion is integral to the successful management of invasive species. Our understanding of how characteristics of resident plant interactions, such as the network architecture of interactions, can affect the invasibility of plant communities is limited. Using a simulation model, we tested how successfully a new plant invader established in communities with different network architectures of species interactions. We also investigated whether species interaction networks lead to relationships between invasibility and other community properties also affected by species interaction networks, such as diversity, species dominance, compositional stability and the productivity of the resident community. We found that higher invasibility strongly related with a lower productivity of the resident community. Plant interaction networks influenced diversity and invasibility in ways that led to complex but clear relationships between the two. Heterospecific interactions that increased diversity tended to decrease invasibility. Negative conspecific interactions always increased diversity and invasibility, but increased invasibility more when they increased diversity less. This study provides new theoretical insights into the effects of plant interaction networks on community invasibility and relationships between diversity and invasibility. Combined with increasing empirical evidence, these insights could have useful implications for the management of invasive plant species.
... The property of habitats or communities determining their susceptibility or resistance to invasions of alien plants is called invasibility [1][2][3]. The number [4][5][6][7] or proportion [6][7][8][9] of alien species in a particular description, habitat, or community is used as a quantitative invasibility characteristic. Sometimes, such parameters as "number/proportion of alien species" are attributed to the "invasion level" (or "level of invasion") characteristic [5,[8][9][10][11][12]; while invasibility is understood as a characteristic of the relative or potential participation of alien plants in a given type of habitat or community under leveled external conditions (urbanization, remoteness from human settle-ments and dissemination foci of alien plant propagules, disturbance, etc.) [3]. ...
... The number [4][5][6][7] or proportion [6][7][8][9] of alien species in a particular description, habitat, or community is used as a quantitative invasibility characteristic. Sometimes, such parameters as "number/proportion of alien species" are attributed to the "invasion level" (or "level of invasion") characteristic [5,[8][9][10][11][12]; while invasibility is understood as a characteristic of the relative or potential participation of alien plants in a given type of habitat or community under leveled external conditions (urbanization, remoteness from human settle-ments and dissemination foci of alien plant propagules, disturbance, etc.) [3]. Therefore, invasibility levels are computed using more mathematically sophisticated formulas compared to invasion levels [2,3,8,[13][14][15]. ...
The purpose of the study was to estimate invasion levels of alien plants in various natural and anthropogenic habitats of the Middle Urals in two urbanization manifestation variants: (1) within the boundaries of a large city; and (2) in suburban areas. In total, 965 geobotanical releves produced in natural (bogs, floodplains, petrophytic areas, meadows, and forests) and anthropogenic (wastelands, public gardens, and residential areas) habitats were analyzed. Natural habitats were surveyed within the boundaries of a large city and in its suburban zone (at distances of 30–40 km from the city). Invasion levels were determined based on the number and proportion of alien (adventitious) species in the description. Both in suburban and urban conditions, the lowest numbers of alien species were recorded in bog habitats (on average, 0–0.6 species per description); while the largest numbers, in anthropogenic habitats (on average, 9.8–17.6 species per description). Outside the city, average numbers of alien species in natural habitats (except for bogs) varied in the range of 1.0–2.8 species per description; within the city, 3.8–6.2 species per description. In natural habitats (except for bogs), average shares of alien species varied in the range of 1.8–5.6% outside the city and in the range of 8.1–16.2% within the city; in anthropogenic habitats, they varied in the range of 22.8–32.8%. Suburban and urban wastelands did not differ in numbers and proportions of alien species (10.3 and 12.9 species per description and 25.3 and 30.2%, respectively). Invasion levels identified in suburban areas are consistent with those recorded in Europe.
... It is important to note that the potential invasiveness of S. squamatum does not depend solely on climatic factors. Instead, its spread is likely influenced by a complex interaction of factors, including habitat suitability, dispersal mechanisms, and anthropogenic influences [100,101]. ...
Understanding the drivers of invasive species’ success is essential for predicting and managing their ecological impacts. Symphyotrichum squamatum, a South American species first recorded in Bucharest in 2015, is currently expanding into urban and peri-urban areas of Romania, raising concerns about its invasive potential. This study provides a comprehensive assessment of its invasiveness by integrating species distribution modeling, a reproductive trait analysis, and morpho-structural evaluations. To deepen our understanding, we compare S. squamatum with S. ciliatum, a species already invasive in Romania, to identify shared traits potentially driving their invasiveness. Using R software (version 4.3.0) with bioclimatic variables, we modeled the potential distribution of both species. The reproductive success of S. squamatum was evaluated through germination tests on seeds from distinct Romanian populations, while anatomical analyses revealed adaptations potentially linked to invasiveness. Our findings indicate that S. squamatum shares traits with successful invaders, as highlighted by its comparison with the invasive S. ciliatum. However, its expansion in Romania appears to be constrained by environmental factors, with continentality emerging as a key determinant influencing the distribution of both species. This study highlights the importance of combining ecological modeling with trait-based analyses to assess invasive potential, offering a robust framework for managing alien species.
... The combined findings led to the development of invasion hypotheses, which can be broadly categorized into those focusing on species traits, community structure, and environmental factors. Starting from the "Baker's rule" and "Tens rule" [4,5], many hypotheses regarding plant invasion emerged, significantly advancing understanding of the mechanisms and factors that contribute to the invasiveness of certain plant species [6][7][8][9]. Analyzing the mechanisms of invasion led to very important insights about competitive advantage of invaders due to chemical peculiarities. The "novel weapon hypothesis" posited that some invasive plants may have stronger allelopathic impacts on other species in introduced ranges than in native ranges because the former may not be as adapted to specific biochemical signatures of invaders compared to species in the native range [10][11][12][13]. ...
Globalization has greatly expanded the opportunities for plant species to enter new areas through a wide range of pathways. Elucidating the pathways of spread of alien species and the characteristics of organisms that make them invasive is one of the most pressing problems in ecological sciences. Once established, alien species may have serious implications for communities and vice versa. Allelopathy has been proposed as one of the possible invasion mechanisms of exotic plants. Impatiens parviflora and Impatiens glandulifera are among the widely spread invasive plant species in the Baltic region. The aim of the study was to evaluate the allelopathic effect of invasive Lithuanian Impatiens spp. and their neighboring plants (11 pristine species) using parameters of germination and seedling growth of biotest species Lepidium sativum, and to expand this study by determining the content of phenolic compounds and the radical scavenging activity in the leaf extracts of Lithuanian Impatiens spp. populations (20 of each Impatiens species). Leaf extracts of all species examined had an inhibitory effect on Lepidium sativum germination and morphology of the seedlings. In our study, at all leaf extract concentrations, significantly higher allelopathic potential on radicle growth was characteristic of I. glandulifera compared to native species Alnus glutinosa, Calystegia sepium, and Urtica dioica. At all leaf extract concentrations, I. parviflora showed significantly higher allelopathic potential on radicle growth compared to native species Urtica dioica. Impatiens glandulifera had a higher juglone index than Impatiens parviflora. I. glandulifera also had the highest juglone index compared to all neighboring species studied. The differences between the populations in the content of phenolic compounds, DPPH and ABTS radical scavenging activity were 2.3, 2.2 and 2.7 times for I. glandulifera and 2.6, 5.2 and 2.7 times for I. parviflora. The mean values of total phenolic content, DPPH and ABTS radical scavenging activity of I. glandulifera populations were 2.1, 2.7 and 3.3 times higher than those of I. parviflora populations, respectively. In general, our results about allelopathic potential and phenolics content, as well as free radical scavenging ability, confirm the supreme competitive ability of I. glandulifera compared to both I. parviflora and to the native co-occurring species.
... Conventional cover crops are gaining traction for production benefits, including weed suppression, erosion control and soil health improvements (Atucha et al., 2020;Gómez et al., 2009). Some native species can compete more strongly with weeds than conventional cover crops (Döring et al., 2012;Richardson & Pyšek, 2006), and diverse species phenology maintain vegetation cover in winter, reducing erosion (De Baets et al., 2007). Persistent vegetation may also increase soil moisture by increasing shading and water infiltration (Gómez et al., 2011). ...
Agroecological restoration aims to restore biodiversity and ecosystem function in agricultural landscapes while sustaining crop production. Adopting native plants as cover crops may restore ecological value to cropping systems such as nut orchards.
We focused on Oregon hazelnut orchards and compared how four seed mixes (native annuals, native perennials, conventional cover crops and unseeded controls) performed under three levels of orchard floor disturbance (flailing, flailing and scraping, and unmanaged/none) across three different orchard ages with corresponding differences in canopy shade over a 2‐year period.
We evaluated cover crop performance by three criteria: the survival criteria (response to disturbance and shading), the production criteria (effects on weeds, erosion potential and soil moisture) and the ecological functioning criteria (abundance and diversity of native plants and pollinator visitations). We found that native species generally outperformed conventional cover crops and bare ground across these criteria.
Plant survival was not affected by disturbance but shading reduced survival of most species. Native annuals had high cover in the first year, and native perennials had high cover across both years. Native perennial species provided the best weed reduction and erosion control while not reducing soil moisture, and hosted the highest pollinator abundances and diversity.
Synthesis and applications. Our results suggest that agroecological restoration of orchards through native cover cropping is a viable strategy for improving ecological outcomes without compromising production needs.
... This is not surprising, given that many NNT species have been selected for their high productivity and rapid growth to satisfy increasing demands for timber or other wood-derived products, or for land reclamation (Richardson, 1998;Castro-Díez et al., 2019b;L azaro-Lobo et al., 2023a). A rapid growth rate has also been shown to be a key trait in the naturalisation of NNT species (Richardson & Pyšek, 2006;Van Kleunen, Weber & Fischer, 2010). We found that carbon loss rates did not differ between NT and NNT forests, suggesting similar decomposition rates of wood, litter, and organic matter. ...
Climate change is one of the main challenges that human societies are currently facing. Given that forests represent major natural carbon sinks in terrestrial ecosystems, administrations worldwide are launching broad‐scale programs to promote forests, including stands of non‐native trees. Yet, non‐native trees may have profound impacts on the functions and services of forest ecosystems, including the carbon cycle, as they may differ widely from native trees in structural and functional characteristics. Also, the allocation of carbon between above‐ and belowground compartments may vary between native and non‐native forests and affect the vulnerability of the carbon stocks to disturbances. We conducted a global meta‐analysis to compare carbon stocks and fluxes among co‐occurring forests dominated by native and non‐native trees, while accounting for the effects of climate, tree life stage, and stand type. We compiled 1678 case studies from 250 papers, with quantitative data for carbon cycle‐related variables from co‐occurring forests dominated by native and non‐native trees. We included 170 non‐native species from 42 families, spanning 55 countries from all continents except Antarctica. Non‐native forests showed higher overall carbon stock due to higher aboveground tree biomass. However, the belowground carbon stock, particularly soil organic carbon, was greater in forests dominated by native trees. Among fluxes, carbon uptake rate was higher in non‐native forests, while carbon loss rate and carbon lability did not differ between native and non‐native forests. Differences in carbon stocks and fluxes between native and non‐native trees were greater at early life stages (i.e. seedling and juvenile). Overall, non‐native forests had greater carbon stocks and fluxes than native forests when both were natural/naturalised or planted; however, native natural forests had greater values for the carbon cycle‐related variables than plantations of non‐native trees. Our findings indicate that promoting non‐native forests may increase carbon stocks in the aboveground compartment at the expense of belowground carbon stocks. This may have far‐reaching implications on the durability and vulnerability of carbon to disturbances. Forestry policies aimed at improving long‐term carbon sequestration and storage should conserve and promote native forests.
... Traditionally, a nonnative species is defined as an organism introduced by humans (accidentally or intentionally) into an area where it has no evolutionary history . The term invasiveness has been commonly applied by institutions such as the International Union for Conservation of Nature or the CBD to describe nonnative species that harm the environment, human health, or the economy and that may also be widespread (Richardson and Pyšek 2006 ). However, these definitions raise some fundamental questions. ...
Invasion science addresses interconnected ecological, economic, and social challenges posed by the introduction of non-native species. Hence, invasion scientists have to consider and reconcile interdisciplinary needs while addressing potential implications of their findings. Navigating diverse disciplines, including environmental sciences, ecology, economics and the humanities, invasion scientists seek to arrive at informed decisions on invasion risk, impact, and management. Individual biases, uncertainties, and systemic pressures influence the ability to maintain objectivity and resist pressures that might otherwise distort findings or applications. This commentary examines conceptual and ethical dilemmas within the field of invasion science, particularly reputational and risks of the discipline perpetuating its own relevance by framing invasions as insurmountable challenges. The discussion highlights how incentive structures, biased assessments and framing, and conflicts of interest may compromise the discipline’s integrity. We also explore questions surrounding human responsibility to animal welfare and highlight ethical conundrums in the management of invasive species.
... This makes riparian ecosystems particularly prone to invasive alien (non-native) plants (IAPs). Alien plants are considered 'invasive' when they become dominant in their introduced range and change the biotic and abiotic conditions of their new environment [3]. This, in turn, can lead to the restructuring of native plant communities and to substantial changes in biodiversity [4,5], along with the modification of ecosystem functioning [6,7]. ...
Riparian softwood forests support numerous ecological functions and high biodiversity. In the context of the LIFE+ Traisen project, a non-regulated new riverbed for the lower Traisen River (“New Traisen”) was created within an artificially lowered floodplain corridor. Using vegetation monitoring from 2014 to 2021, we determined (i) the role of Solidago gigantea in the establishment of softwood forests, (ii) the habitat parameters (such as flooding height, fine substrate layer thickness, and vegetation cover) that impact the establishment and growth of woody plants, and (iii) the successional phase at which woody plants become established, as well as the potential creation of new germination habitats. During early succession, the softwood species, as light-tolerant pioneer species, colonized the open sites together with S. gigantea and subsequently established a floodplain softwood forest. Unexpectedly, we observed negative forest development only when the S. gigantea cover exceeded 90%. Neither the habitat parameters nor S. gigantea cover significantly impacted tree occurrence. However, we highlight the need for optimum habitat parameters for softwood forest development in early succession phases, ideally before S. gigantea forms dense, monospecific stands. Tailored monitoring strategies are needed to guide the succession of such semi-aquatic habitats toward the development of the desired habitat type.
... Enemy release in the invaded range (i.e., the loss of predators, parasites and competitors, Brian & Catford 2023;Keane & Crawley, 2002) can lead to an expansion of the realised niche in new environments free of native antagonists. Species with traits typically associated with slow resource acquisition, such as short stature, slow growth and big seeds (e.g., Gioria et al., 2023;Richardson & Pyšek, 2006;van Kleunen, Weber & Fischer, 2010), are poor competitors in disturbed areas and may be more likely to expand their niche when they are released from their antagonists that otherwise limit their establishment. In contrast, plant species that are highly competitive in resource acquisition at home (e.g., high SLA) might be relatively unaffected by release from competitors, especially in disturbed habitats. ...
Aim
Humans have spread plants globally for millennia, inadvertently causing ecological disruptions. However, biological invasions also provide a unique opportunity to study the process of niche dynamics, through which species adapt their niche when confronted with novel environments. Focusing on the Mediterranean Basin, we assessed 1) which traits favour niche dynamics, and 2) whether niche conservatism or niche shift promotes invasion success.
Location
Mediterranean Europe and the World.
Methods
We selected the 85 most widespread alien vascular plants in Mediterranean Europe and compiled data on their distribution in their native and invaded ranges. We then tested how a species' residence time, biogeographic origin, dispersal ability, functional traits and intraspecific trait variability (ITV) influence its niche dynamics following invasion. Using already published independent data, we finally assessed whether niche dynamics can explain different dimensions of invasion success (such as regional spread or local abundance).
Results
We found that niche shifts were common (71% of species) and were mostly driven by species failing to occupy all suitable environments of their invaded range (unfilling), regardless of residence time. Niche unfilling and niche expansion were more important in species with high intraspecific trait variability introduced from non-mediterranean biomes (temperate or tropical). Niche expansion was also greater in species with long-distance dispersal, bigger seeds and a narrow native niche. Interestingly, invasion success correlated more with a species’ ability to conserve its niche and residence time than with niche expansion.
Main conclusions
Niche shifts were better predicted by species traits than residence time. For example, high adaptive potential (inferred from high intraspecific trait variability) favoured niche shifts in general, and long-distance dispersal favoured niche expansion. Understanding how these traits relate to niche dynamics is important since a species' ability to conserve and fill its niche is in turn a good predictor of invasion success.
... Specifically, approximately 10% of species transported beyond their native range will be released or escape in the new regions, about 10% of these introduced species will successfully establish themselves, and about 10% of established species will become invasive (tens rule; Williamson and Fitter 1996). Therefore, extensive long-term research has been conducted to identify which environments facilitate the establishment of invasive species and which species' characteristics contribute to the successful establishment (Richardson and Pyšek 2006;Hayes and Barry 2008;Hui et al. 2016). ...
Invasive alien plants cause severe global problems; therefore, determining the factors that lead to the success or failure of invasion is a critical question in the field of invasion ecology. In this study, we aimed to determine the factors underlying differences in the distribution range of alien plants in Japan by investigating why Lolium multiflorum thrives in a wide range of habitats while L. rigidum is mainly distributed on sandy beaches. We initially evaluated environmental niche suitability through species distribution modelling and subsequently examined whether species traits influence the differences in range expansion between the two species. We used MaxEnt modelling to identify potential environmental niches for both species. The analysis revealed that L. rigidum was considerably less suited to the Japanese climate compared to L. multiflorum, with high summer precipitation in Japan identified as one of the climatic factors limiting the distribution of L. rigidum. Given that these winter annual plants remain dormant as seeds during summer, in subsequent experiments, we buried seeds in paddy field soil and sandy beach sand during summer and evaluated their survival rate in autumn. The survival rate of L. rigidum seeds was significantly lower than that of L. multiflorum, particularly in paddy soil. Factors contributing to seed mortality may include the decay or early germination of L. rigidum seeds under Japan’s high rainfall conditions. This study emphasises the importance of considering local environmental factors alongside climate niche modelling in the risk assessment of invasive species. Moreover, the integration of species distribution modelling for large-scale evaluations and manipulation experiments for fine-scale assessments proved effective in identifying climatic conditions and species traits influencing the success or failure of alien species invasion.
... Its ability to regenerate from seeds and vigorously resprout from its extensive root system contributes to its persistence and makes eradication efforts particularly challenging [37]. Moreover, U. europaeus has allelopathic properties, releasing chemicals that inhibit the growth of other plant species, further hindering restoration endeavors [48]. Despite the implementation of various control methods such as manual removal, herbicide application, and biological control agents, achieving complete eradication of U. europaeus remains elusive in many regions [20,38]. ...
Invasive plant species have been recognized as adversely affecting native ecosystems. Some of these plant species become problematic in disturbed environments such as urbanized, agricultural, and abandoned developed or farmed land. In some cases, they can dominate the invaded ground, preventing a transition back to the native plant community. In Tenerife (Canary Islands), the invasive plant species Ulex europaeus L. has established dense infestations in abandoned agricultural lands. Removing such invasive species in Tenerife through ecological restoration is crucial for restoring ecosystem functionality and promoting biodiversity. This study evaluates various management methods for U. europaeus in abandoned fields, assessing their impact on species richness, diversity, composition, and regeneration. The findings can inform management strategies to combat this invasive species, contributing to biodiversity conservation and ecosystem resilience. The study was conducted in two highly invaded areas, evaluating chemical (C), mechanical (M), mechanical and chemical (MC), and mechanical, chemical, and plantation treatments (MCP), along with a control, to analyze changes in species richness, diversity, and plant community. Results indicate that U. europaeus remains capable of reoccupying treated areas. The different treatments led to differences in species richness and composition. The MCP treatment yielded the best results if the planted native species grew faster than Ulex europaeus, preventing its establishment due to its shade-intolerant nature. However, continual control is required to eliminate U. europaeus regeneration from seeds that can persist for at least 30 years.
... The minimum residence time refers to the time elapsed since the initial recording of an alien species (Richardson & Pyšek 2006). To estimate the species' minimum residence time, we used the earliest record of the species occurrence in the region based on the rst records in the scienti c literature and/or herbarium records (Hooker, 1875;Stewart, 1972;Kachroo et al., 1977;Gulzar et al., 2023). ...
Biological invasions pose a significant threat to sustenance of biodiversity and ecosystem services, with their incidence expected to rise due to globalization and climate change. Regional inventories of alien species are important for monitoring and managing the biological invasions, particularly in world’s mountains which till recently were immune to invasions but are increasingly becoming vulnerable to invasive species. This study presents the first comprehensive inventory and status assessment of the alien flora in Ladakh – a remote and unique biogeographic region in Indian Trans-Himalaya. Based on field data collected from 2018 to 2023, we provide taxonomic composition of alien flora in Ladakh, including information on invasion status (cultivated, naturalized and invasive), biogeographic affiliation, habitat and life-form characteristics, and pathways of introduction. In total, we recorded 104 alien plant species, accounting ∼ 5.7% to the region's flora. Of these, 24 alien species are under cultivation, while the remaining 80 are aliens growing in wild, with 52 naturalized and 28 invasive. The most species-rich families are Asteraceae (20 species), Amaranthaceae (12 species), Poaceae (7 species), Salicaceae (6 species), and Fabaceae (5 species). Most alien species in the region are native to temperate Asia (34 species), followed by Europe (30 species). The alien species primarily colonize human-dominated habitats, such as roadsides and agricultural fields. Additionally, we found that the elevational distribution of the alien species richness in the region exhibits a unimodal hump-shaped pattern, with the highest number of alien species (73 species) occurring between 2600–3000 meters. The elevational width and maximum elevation of alien species was positively correlated with the maximum elevation in their native region. In an era of rising risks of climate change and rapid land-use transformation in the Himalayan highlands, this first assessment of the alien flora of the Ladakh will foster further research, inform early eradication, and guide pro-active plant invasion management in the region, with lessons for such environments elsewhere.
... The impact of IAPs on native vegetation has been shown to vary from one invasive species to another (Richardson and Py sek, 2006;Hejda et al., 2009Hejda et al., , 2017 with the greatest impact most often being exerted by those species which form monocultures and have higher densities than native species (Hejda et al., 2009;Hejda and Py sek, 2006). Plant invasions can reduce native plant and animal species diversity, richness and evenness to varying degrees (L opez Rosas et al., 2005;Hejda et al., 2009;Kie»tyk and Delimat, 2019) as well as alter soil physiochemical status (Afreen et al., 2018;Stefanowicz et al., 2018;Vanderhoeven et al., 2005;Vila et al., 2006). ...
Nassella trichotoma (Poaceae) is a highly invasive South American grass that is invading montane grasslands in the Eastern and Western Cape provinces of South Africa. Although N. trichotoma has been recognised as a major problem in these mountains for decades, the primary concern has been on impacts on rangeland productivity and management, while the impacts of invasions on plant biodiversity have not been considered. To understand the impact of N. trichotoma on local plant biodiversity, 81 pairs of plots (total of 162 plots) were laid out in the Sneeuberg and Eastern Cape Drakensberg mountains, Eastern Cape, in March 2020 and March 2021. At each site plots were located in grassland invaded by N. trichotoma and in nearby uninvaded grassland (control). A total of 20 N. trichotoma patches were sampled with two to four plot pairs per site. All vascular plant species were recorded in all plots, the cover abundance of each species per plot was visually estimated, and the topsoil was sampled and analysed for differences in nutrient and physical factors between invaded and uninvaded plots. Plant species diversity was 24 % higher in uninvaded areas, and the native grasses Pentameris airoides (X 2 = 4.93, d.f. = 1, p < 0.01), Tenaxia disticha (X 2 = 5.51, d.f. = 1, p < 0.01), and The-meda triandra (X 2 = 9.28, d.f. = 1, p < 0.001) were significantly less abundant in invaded plots. Uninvaded areas had greater native species diversity (65 species) and fewer alien species (3) than invaded areas (47 and 9 respectively). Of the 18 soil variables measured, the following were significantly higher in invaded areas than uninvaded areas: boron (23 %), calcium (18 %), phosphorous (58 %), silt (10 %), total cations (12 %), and zinc (68 %). This suggest that N. trichotoma alters soil nutrients. The results indicate that N. trichotoma is a powerful driver of native biodiversity erosion in these montane grasslands and should be a cause for major concern by landowners and government.
... Previous studies analyzed the role of functional traits such as specific leaf area and CO 2 assimilation (Baruch and Goldstein 1999;Grotkopp and Rejmánek 2007), root mass allocation and nitrogen fixation ability (Morris et al. 2011), phenotypic plasticity (Richardson and Pyšek 2006) and reproductive characteristics (van Kleunen et al. 2007) for plant invasiveness. For example, enhanced seed germination and high relative growth rate (RGR) of seedlings are key traits that can contribute to the successful invasion of several alien plant species into new environments (Burns 2004;Kharel et al. 2024;Mandák 2003). ...
... Because only a fraction of introduced plant species establish and spread to the degree they are considered noxious weeds, it is critical to understand the processes underpinning this success in order to prevent further spread or to manage their negative impacts (Blackburn et al., 2011, Parker et al., 2013, Gioria et al., 2023. Myriad studies in the last two decades have investigated the characteristics of successful invaders and/or susceptible recipient ecosystems Pyšek, 2006, Pyšek andRichardson, 2007) and generated predictions about which species may pose threats or under what conditions they will impact receiving-habitats (Catford et al., 2009). Interactions between introduced species and natural enemies has generated considerable scholarship and contributed to development and refinement of population and community ecological theory Pyšek, 2006, Gioria et al., 2023). ...
Natural or anthropogenic movement of plant species outside their historical ranges may result in exposure to new environmental conditions and a lack of natural enemies, thus promoting their establishment and spread into new areas. A biogeographical comparison of native and invasive populations can provide insight into the mechanisms of successful invasions and guide effective management strategies, such as biological control, by targeting plant traits that promote invasiveness. We studied the Eurasian aquatic plant, Nymphoides peltata, in situ in the native (China, Korea) and invaded (USA) ranges to determine whether there were differences in natural enemy attack rates (percent leaf damage, frequency of leaf herbivory or disease), productivity (plant cover, reproduction), and leaf traits (leaf elemental content, leaf toughness, dry matter content, specific leaf area) between areas. We also investigated whether there was evidence of a tradeoff between natural enemy attack and growth or reproduction, as would be predicted by invasion theory. Plant cover (23-29 % higher) and reproductive output (eight times more seeds / m 2) were consistently higher in the invaded range. Leaf traits consistently differed between ranges, which we would expect if plants in the invaded range had fewer herbivores or other pests. The amount of leaf damage present was similar between ranges, but the frequency of herbivory was 50 % greater, on average, in the native than invaded range. Although we did not quantify suppression of N. peltata by natural enemies, we found evidence of more frequent herbivory in Asia and reduced reproduction and plant cover compared to the USA, which supports further investigation into viability of biological controls.
... Biological invasions, representing one of the main components of global change, can have negative consequences on the structure, function and dynamics of ecosystems [1]. The success of biological invasions depends on a species' potential to colonize new habitats (e.g., high dispersal efficiency, the persistence of the seed bank, and population density) and on its competitive ability against native plant species (i.e., fast plant growth in terms of higher biomass production and high regeneration capacity; see [2]). ...
Plastic traits are argued to favor the establishment of invasive alien plants and to evolve during the invasion process, so that invasions may be favored by both plasticity and evolutionary changes in plasticity. Despite this aspect being pivotal to understanding invasion processes, no information is available about the effect of residence time on the evolution of phenotypic plasticity of aliens to produce locally adapted phenotypes. Therefore, we aimed to evaluate changes in the morpho-functional traits of the invasive alien Ambrosia trifida L. over time. Specifically, we grew A. trifida plants under laboratory (at different temperatures: 10 • C, 20 • C and 25 • C) and field conditions by using seeds collected from 2011 to 2020 from an Eastern European population. Data about seedling emergence, vegetative (laboratory and field) and reproductive (field) traits were collected, e.g., maximum plant height (cm), total dry biomass (g), number of flowers (n) and number of new seeds (n). Analysis of variance (ANOVA), linear regressions and a plasticity index were applied to assess differences in plant performances when grown from seeds of different ages. An auto-regressive integrated moving average (ARIMA) model was applied to predict future trends of some key plant traits (maximum height, total dry biomass and number of new seeds). Overall, the time of seedling emergence was not statistically different among seeds of different age, and regression analyses exhibited a positive relationship between residence time (seed age) and vegetative and reproductive parameters of A. trifida. Only male flower production exhibited a negative trend over time. At all temperatures (especially at 25 • C), the vegetative parameters increased with the decrease in residence time. The plasticity index of the measured traits tended to decrease over time for most traits both in the field and in the laboratory trials. The ARIMA model predicted that plant traits will continue to increase in size over time by 2030, suggesting further plastic adaptation of A. trifida. The results highlighted that residence time influences the evolution of phenotypic plasticity of A. trifida, which has strengthened its adaptability to the new conditions over a decade, also demonstrating a great adaptive and invasion potential for the future.
... proximity to human-altered landscapes or source populations) can also drive invasion success, even for species lacking the functional traits associated with high performance (Davis et al., 2000;Ni et al., 2021). Despite the rich literature describing biological invasions, the influence of disturbances and disturbance-mediated community characteristics on the functional strategies of co-occurring native and non-native species has rarely been quantified or investigated across broad environmental gradients and varied forest communities (Perkins et al., 2011;Richardson & Pyšek, 2006). ...
Although disturbance is considered a major driver of plant invasions across many systems, our understanding of the mechanisms by which disturbance mediates understorey invasions in natural forests is limited.
We used a national natural forest inventory dataset spanning New Zealand's wide climatic and soil fertility gradients to disentangle disturbance‐mediated community characteristics driving abundance, species richness and functional composition of understorey plant invasions.
Disturbance‐mediated declines in canopy tree abundance and increases in soil fertility and pH increased non‐native plant richness and cover relative to co‐occurring native plant assemblages. Cover of non‐native species also increased with proximity to anthropogenic land cover.
Non‐native plant assemblages had higher community‐weighted mean (CWM) values for specific leaf area (SLA) but lower CWM values for height and woodiness relative to native assemblages irrespective of disturbance. However, greater nearby anthropogenic land cover drove increased woodiness in non‐native assemblages but decreased woodiness in co‐occurring native assemblages.
Synthesis: Our study provides the first national‐scale evidence that canopy disturbance effects on soil properties increase both richness and abundance of non‐native plants in natural forest understories. We also revealed functional trait differences between native and non‐native assemblages (SLA in particular), which could alter fundamental forest ecosystem processes like litter decomposition and nutrient cycling. Finally, landscape‐scale anthropogenic impacts may exacerbate forest invasions by increasing non‐native abundance and favouring woody invaders, which may achieve dominance in future forest communities over the longer‐term.
... These results are in line with the hypothesis that different invasion stages (i.e., introduction, naturalisation and spread) are dominated by different genotypes. In theory, it is likely that invasive populations of any species include genotypes of differential fitness (Richardson and Pyšek 2006;Theoharides and Dukes 2007;Zenni et al. 2014). An alternative explanation is that colonisation of new areas away from plantations involved only a few individuals which could erode the genetic diversity along the route of expansion due to consecutive founding events (Austerlitz et al. 1997;Dlugosch and Parker 2008). ...
To understand the success of invasive alien species, it is necessary to evaluate the site-specific eco-evolutionary challenges they face in their new environments. We explored whether the rearrangement of genetic diversity is linked to the invasiveness of Prosopis juliflora by (i) comparing different stages of invasion (founding vs invasive populations) in two invaded areas (Afar Region, Ethiopia and Baringo County, Kenya) to evaluate whether different stages are dominated by different genetic attributes (e.g., characteristic genotypes or levels of genetic diversity) and by (ii) evaluating if landscape features affected dispersal between invasive populations in the two invaded areas. We hypothesised that different invasion stages would have unique genetic characteristics due to either site-specific demographic and/or dispersal dynamics. We also compared the genetic characteristics at an ‘invasive–non-invasive congener’ level by studying the non-invasive P. pallida, introduced to Baringo County, and assessed whether it hybridises with P. juliflora. In the Afar Region, the establishment and spread of P. juliflora were characterised by extensive gene flow that homogenised genetic diversity across all populations. In contrast, in Baringo County, invasive populations had lower genetic diversity than founders, and genetic differentiation was lower between invasive populations than between invasive and founder populations. In both invaded areas, we found no evidence that dispersal was hampered by geographic distance, bioclimatic conditions, or distance to roads, rivers and villages, at least at the spatial scales of our study; indicating frequent long-distance dispersal. Allelic richness was higher in P. juliflora than P. pallida founders and hybrids were mainly planted trees probably resulting from the sympatric cultivation of the two species following their introduction. Thus, management actions on Prosopis invasion in eastern Africa should consider site-specific dynamics occurring during the invasion.
... Studies of this hypothesis have yielded contradictory results (Fridley et al., 2007;Smith and Côté, 2019;Ernst et al., 2021;Elton, 1958), indicating both positive and negative relationships between species richness and invasibility. This indicates that the negative association between diversity and invasibility does not exist in all ecosystems (Davies et al., 2005;Herben, 2005;Richardson and Pyšek, 2006). ...
Understanding the relationship between plant diversity and invasibility is essential in invasion ecology. Elton proposed that species-rich communities are more resistant to invasions than species-poor communities. While soil microorganisms play a crucial role in regulating this diversity–invasibility relationship, the effects of plant competition mode and soil nutrient status on their role remain unclear. To address this, we conducted a two-stage greenhouse experiment. Soils were first conditioned by growing nine native species separately in them for one year, then mixed in various configurations with soils conditioned using one, three, or six species, respectively. Next, we inoculated the mixed soil into sterilized substrate soil and planted the alien species Rhus typhina and native species Ailanthus altissima as test plants. We set up two competition modes (intraspecific and interspecific) and two nutrient levels (fertilization using slow-release fertilizer and non-fertilization). Under intraspecific competition, regardless of fertilization, the biomass of the alien species was higher in soil conditioned by six native species. In contrast, under interspecific competition, the biomass increased without fertilization but remained stable with fertilization in soil conditioned by six native species. Analysis of the soil microbial community suggests that the greater diversity of arbuscular mycorrhizal fungi (AMF) in the soil conditioned by six native species might reflect the primary influence on R. typhina growth, but the interaction between AMF and R. typhina varies depending on competition mode and nutrient status. Our findings suggest that the soil microbiome is pivotal in mediating the diversity–invasibility relationship, and this influence varies with competition mode and nutrient status.
... This indicates that the negative association between plant diversity and invasibility does not exist in all ecosystems (Davies et al., 2005;Herben, 2005;Richardson & Pyšek, 2006). ...
Understanding the relationship between plant diversity and invasibility is essential in invasion ecology. Species‐rich communities are hypothesized to be more resistant to invasions than species‐poor communities. However, while soil microorganisms play a crucial role in regulating this diversity–invasibility relationship, the effects of plant competition mode and soil nutrient status on their role remain unclear. To address this, we conducted a two‐stage greenhouse experiment. Soils were first conditioned by growing nine native species separately in them for 1 year, then mixed in various configurations with soils conditioned using one, three, or six species, respectively. Next, we inoculated the mixed soil into sterilized substrate soil and planted the alien species Rhus typhina and native species Ailanthus altissima as test plants. We set up two competition modes (intraspecific and interspecific) and two nutrient levels (fertilization using slow‐release fertilizer and nonfertilization). Under intraspecific competition, regardless of fertilization, the biomass of the alien species was higher in soil conditioned by six native species. By contrast, under interspecific competition, the biomass increased without fertilization but remained stable with fertilization in soil conditioned by six native species. Analysis of soil microbes suggests that pathogens and symbiotic fungi in diverse plant communities influenced R. typhina growth, which varied with competition mode and nutrient status. Our findings suggest that the soil microbiome is pivotal in mediating the diversity–invasibility relationship, and this influence varies according to competition mode and nutrient status.
... 17 This term is well established in ecology, where it describes the vulnerability of a habitat to be invaded by foreign species. 18,19 In the case of tissues, the invasive cell type can be a cancer cell population, the extra villous trophoblast cells of the placenta or a iScience Article leukocyte. In brief, the model claims that the nature of the fetal-maternal interface is determined by the invasibility of the uterine endometrium (reviewed in the study by Wagner et al. 16 ) and that the evolution of endometrial invasibility by placental cells will lead to correlated changes in the invasibility of somatic tissues, thus leading to a corresponding change in invasibility by cancer cells of other parts of the body. ...
The success of invasive species can be measured by invasiveness, which depicts intrinsic characteristics that enable them to thrive in new environments. In invasive seaweeds, for example, the persistence of multiple overlapping cohorts throughout the year plays a key role in increasing plant cover and exerting unrelenting pressure on invaded areas. The marine brown macroalgae Rugulopteryx okamurae has recently established abundant populations in the Mediterranean Sea and Atlantic Ocean, negatively affecting both biodiversity and socioeconomic factors by unprecedently aggressive invasive behaviour. The objective of the study is to understand the invasiveness of R. okamurae through its popu lation dynamics. For this, a year-round study was conducted in a protected habitat of Posidonia oceanica in southern Spain, revealing that R. okamurae uses alternating mechanisms for population maintenance. It achieves high density of young individuals in late summer and autumn, peaking at 3285 individuals per square metre. In spring and early summer, the population shifts towards fewer – but larger – individuals, with densities dropping to 888 individuals per square metre and biomass reaching a peak of 170 g dry weight (DW) per square metre. Six overlapping cohorts were identified by Gaussian curves. They persisted throughout the year, but they were not related to environmental factors, which indicates adaptive physiological mechanisms that sustain dense monospecific populations. Additionally, the association between cohorts and different morphotypes suggests that R. okamurae phenotypic plasticity enables its persistence in introduced areas. These findings provide valuable insights into the biological traits underpinning its invasiveness in P. oceanica meadows, revealing temporal windows of invasiveness driven by different mechanisms. This knowledge is crucial for developing effective conservation and management strategies aimed at mitigating the impact of this invasive species.
Riparian forests are among the most vulnerable ecosystems to biological invasions. Effective management
strategies require a nuanced understanding of both species invasiveness and environmental conditions, but
analysing these interactions is complex. We designed an Agent-Based Model (ABM) to simulate the spatio-
temporal spread of Gleditsia triacanthos in the riparian forest of the Esteros de Farrapos e Islas del Río
Uruguay National Park; Uruguay. This is a parsimonious and generalisable model that incorporates distinctive
features of woody invasions in riparian systems—such as environmental heterogeneity and flooding regimes—as
well as common characteristics of woody invaders. Management simulations suggest that if control measures are
maintained over time, the abundance of the invader will remain constant at low levels; thus, the invasion can be
controlled, even if not completely eradicated. The results also indicate that without control, the invasion process
would spread even into unsuitable areas. The SWIRS model facilitates the evaluation of targeted management
strategies, ultimately providing a framework to enhance biodiversity conservation efforts in riparian ecosystems.
Canarias conserva una importante biodiversidad de flora endémica, una lista que continúa incrementándose con numerosos estudios recientes. Sin embargo, hay pocos estudios sobre los rasgos funcionales de las especies, especialmente aquellos que conllevan mediciones directas en campo, pese a la importancia que esto puede tener en el actual contexto de cambio climático. Las variaciones de la tasa de productividad vegetativa y reproductora entre poblacionales de diferentes islas, o dentro de una misma isla, pueden implicar diferencias en la capacidad de respuesta al cambio climático. Aquí analizamos el esfuerzo reproductor de las especies del género Descurainia en Canarias, con el objetivo deevaluar si existen diferencias interespecíficas e intrapoblacionales en este rasgo funcional. Además, se pretende determinar cuál de los dos tipos de variables (climáticas o morfométricas), tiene mayor peso en la explicación del esfuerzo reproductor de las especies del género. Para ello, se seleccionaron al azar 45 individuos en tres poblaciones distribuidas en cada isla. Cada individuo fue medido y contabilizado el número de flores y semillas por unidad de superficie (cm2). Los resultados muestran diferencias significativas entre especies y entre poblaciones. Además, los modelos obtenidos indican que las variables climáticas explican mejor el esfuerzo reproductivo que las variables morfométricas.
The mating system of non-native plant populations plays a role in determining the colonizing success following introduction into locations outside of the native distribution. For plant species capable of mixed-mating, both selfing and outcrossing can be advantageous and promote the establishment, persistence, and spread of newly arrived populations. To investigate how mating systems may contribute to the invasion process we estimated mating system parameters in perennial populations of the model plant species, Mimulus guttatus from its native range (West coast USA), non-native populations that are established but have not become invasive (East coast USA, >50 years), and populations in invasive regions (UK >200 years). Studies that include mating system data across the continuum of the invasion process are rare, thus here we utilize molecular markers to estimate outcrossing rates (t), inbreeding coefficients (F), and inbreeding depression in native, naturalized, and invasive populations. Overall, we found support for the persistence of mixed-mating across populations, variability in the relationship between outcrossing rates and inbreeding depression across populations, and evidence for the bridgehead process, where non-native populations may be the sources for the further establishment or reinforcement of additional non-native populations. The methodology we deployed had its own assumptions and sampling design constraints, that contributed to the variation in the parameter estimates. All M. guttatus populations likely rely on selfing through both within clone, and within flower and plant mating in addition to vegetative propagation. The results underscore the importance of introduction history in determining the role of both sexual and asexual reproduction in the successful establishment of a plant species outside its native range.
Although herbivory and allelopathy play important roles in plant invasions, their roles in mediating the effect of plant diversity on invasion resistance remain unknown. In a 2‐year field experiment, we constructed native plant communities with four levels of species richness (one, two, four, and eight species) and used a factorial combination of insecticide and activated carbon applications to reduce herbivory and allelopathy, respectively. We then invaded the communities with the introduced plant Solidago canadensis L. One year after the start of the experiment, there was no statistically significant net effect of species richness on biomass of the invader. However, a structural equation model showed that species richness had a positive direct effect on invader biomass that was partially balanced out by a negative indirect effect of species richness via increased light interception. In the second year, the relationship between invader biomass and species richness was negative when we analyzed the treatment combination with herbivory and allelopathy separately. Therefore, we conclude that joint effects of herbivory and allelopathy may play major roles in driving the diversity–invasibility relationship and should be considered in future studies.
Aim
We aim to investigate whether invasive alien plants introduced at different times exhibit variations in elevational distribution patterns and to explore the correlations of these patterns with climate, native plants and human activity.
Location
Guangxi, China.
Methods
We recorded plant richness and cover across elevational gradients at 25–34 sites within each reserve, utilising 84–134 roadside plots per site. Using generalised linear mixed model (GLMM), we assessed the impacts of climate, native plants and human activity on the distributions of all, old and new invasive alien plants across the region and within the nature reserves.
Results
At regional scales, the cover of all, new and old invasive alien plants decreased with increasing elevation, while only the richness of old invasive alien plants exhibited a similar pattern. Contrasting patterns were observed in Dayao Mountain, where the cover of old invasive alien plants decreased while the cover of new invasive alien plants increased. The richness patterns of all and new invasive alien plants were opposite between Dayao Mountain and Yachang Orchid. Moreover, native plant richness was negatively correlated with the richness of invasive alien plants, while interference intensity positively affected new invasive alien plants at both regional and reserve scales. At the regional scale, native plant richness accounted for 78.27%, 91.94% and 60.9% of all, old and new invasive alien plants respectively. Interference intensity accounted for 33.85% of the variation in new invasive alien plants. Annual mean temperature positively influenced the cover of all and old invasive alien plants at both regional and reserve scales, explaining 36.91% and 74.28% of their regional variation. Additionally, interference intensity and distance to human settlements positively impacted the cover of new invasive alien plants, contributing to 50.95% and 31.92% of their variation at regional scales.
Main Conclusion
The distinct distribution patterns of old and new invasive alien plants highlight the significance of residence time in understanding their dynamics. Climate factors constrain the cover distribution of all and old invasive alien plants, whereas interference intensity and distance to settlements determine the distribution of new invasive alien plants. Notably, native plants play a vital role in preventing the establishment and spread of invasive alien plants within nature reserves, and their effectiveness increases with longer residence times. Our findings highlight the critical importance of minimising human interference and conserving native species for the effective management of invasive alien plants in nature reserves.
The degree of domestication can influence the ability of introduced species to survive and reproduce. Species with higher degrees of domestication are highly dependent on humans for survival and reproduction. On the other hand, lower degrees may result in lower survival rates and reproduction output. However, the interrelationship between degrees of domestication and plant invasion remains underexplored. We focused our study on plant species native to the Americas with distinct degrees of domestication, with fruits used for human consumption, to test the hypothesis that plants with intermediate degrees of domestication show higher invasion potential than plants with lower or higher degrees of domestication. We calculated an invasion potential index as the ratio between the number of checklists where an introduced species was recorded as invasive and the total number of checklists where it was registered as introduced. Our results show a negative non-linear relationship between the degree of domestication and invasion potential. While species with intermediate degrees of domestication show higher invasion potential than those fully domesticated, species with the lowest degrees of domestication showed the highest invasion potential. These findings suggest that full domestication does not eliminate invasion risk, highlighting the complexity of the relationship between domestication and invasion. Our results provide valuable insights to support public policies, inform future studies on plant invasions, and the need for management strategies that consider different degrees of domestication.
Riparian zones, interfaces between aquatic and terrestrial ecosystems, are known to support distinct floral elements which play vital ecological functions. For recording the diversity of floral elements in these habitats, a survey of riparian zones was undertaken in Kashmir Valley which revealed occurrence of 265 plant species belonging to 46 families and 170 genera. Riparian areas of this region are dominated by alien species as they represented 74.72% (198 species) while as native species represented only 25.28% (67 species). Of the 198 alien species, 84 were invasive, 100 were naturalized, 9 were casuals and 5 were casual or naturalized. Most of the species inhabiting these habitats were herbaceous perennial species. In comparison to riversides, number of species per site and mean values of diversity indices were higher in streamsides. In addition, riversides were characterised by highest level of invasion expressed both as proportion of aliens and invasives. High level of invasion in riversides is because of high level of disturbances in these habitats in comparison to streamsides which in turn has resulted in low levels of species diversity in these habitats. This high percentage of alien species in riparian habitats is alarming for the region as the connected nature of rivers and streams is likely to spread alien plant species to distant places in the region. This study provides baseline knowledge about the species composition and diversity patterns of these important vegetation zones which will help in their proper management in view of the spread invasive plants in the region.
Background and Aims
Invasive species usually demonstrate remarkable adaptability across diverse environments, successfully inhabiting a wide variety of regions. This adaptability often links to genetic differentiation and phenotypic plasticity, leading to latitudinal trends in phenotypic traits. In this study, we collected seeds of invasive plant Phytolacca americana from different latitudes and planted them in homogeneous gardens to investigate the latitudinal variation of P. americana phenotypic traits and to evaluate the effects of herbivory and heavy metals on plant growth, defence, and reproductive characteristics.
Methods
P. americana seeds from different latitudes were planted in a homogeneous garden. For the experimental treatment, the seeds were divided into four groups: a heavy metal treatment group and its corresponding control group, and a cover treatment group with its corresponding control group. After the fruits matured, their growth, reproduction, and defence indicators were measured.
Key Results
Significant latitudinal trends were observed in P. americana’s growth and defence characteristics, including changes in branch number, underground biomass, total biomass, and leaf tannin content. Compared to previous field surveys on P. americana, our study found that the latitude trends in growth structure and defence traits were consistent. But the latitudinal trend of reproductive structure is different. Moreover, heavy metals and herbivory substantially influenced the plant’s growth, reproduction, and defence mechanisms, further shaping its latitudinal patterns.
Conclusions
The observed phenotypic variations in P. americana across latitudes can be largely attributed to the synergistic effects of phenotypic plasticity and genetic variation. At a broader geographical scale, adaptations to heavy metal stress and herbivory pressure among different P. americana populations involve distinct trade-offs related to growth, reproduction, and defence strategies.
Elton’s biotic resistance hypothesis posits that species-rich communities are more resistant to invasion. Yet, there is evidence that species richness alone may not fully explain community resistance, as phylogenetic and functional richness, along with environmental factors and human-induced disturbances, also play pivotal roles. Additionally, it remains unknown how these factors collectively affect plant invasion as alien species progress along the introduction-naturalization-invasion continuum. For 12,056 local plant communities of Central Europe, we investigate how these factors affect the presence and richness of alien species at different stages along the invasion continuum. Our study reveals varying effects of these factors on the presence and richness of alien species at different invasion stages, highlighting the complexity of the invasion process. Specifically, we demonstrate although species richness and functional richness of resident communities had mostly negative effects on alien species presence and richness, the strength and sometimes also direction of these effects varied along the continuum. By uncovering the stage-dependent effects of these factors, our study not only offers a more nuanced understanding of Elton’s biotic resistance hypothesis but also suggests that other invasion hypotheses should be carefully revisited given their potential stage-dependent nature.
Elton’s biotic resistance hypothesis posits that species-rich communities are more resistant to invasion. However, it remains unknown how species, phylogenetic and functional richness, along with environmental and human-impact factors, collectively affect plant invasion as alien species progress along the introduction–naturalization–invasion continuum. Using data from 12,056 local plant communities of the Czech Republic, this study reveals varying effects of these factors on the presence and richness of alien species at different invasion stages, highlighting the complexity of the invasion process. Specifically, we demonstrate that although species richness and functional richness of resident communities had mostly negative effects on alien species presence and richness, the strength and sometimes also direction of these effects varied along the continuum. Our study not only underscores that evidence for or against Elton’s biotic resistance hypothesis may be stage-dependent but also suggests that other invasion hypotheses should be carefully revisited given their potential stage-dependent nature.
La ville d’Abidjan connaît une urbanisation marquée par une crise multiforme. Elle
s’aperçoit principalement par la rapide croissance démographique entrainant la
déstructuration du cadre de vie. Cocody, commune du district d’Abidjan en est une parfaite illustration. Elle abrite sur son territoire des quartiers frappés par cette crise de l’urbanisation. La présente étude s’intéresse à Colombie, un bloc d’habitation spontanée dans le quartier des 2 plateaux. L’objectif poursuivi par cet article est d’y identifier les formes de dégradation du cadre de vie. Spécifiquement, il est question d’évaluer le niveau de dégradation du cadre de vie.
La méthode de collecte des données a consisté à un pointage des formes de dégradation du cadre de vie avec un GPS. L’examen d’une image satellitalle de type quick bird couplée à une observation directe ont permis de procéder à l’occupation du sol. Un modèle de quantification de la dégradation du cadre de vie a été élaboré à l’issue de notre démarche.
Les valeurs indiciaires obtenues ont été cartographiées suivant un procédé de
représentation par carroyage.
Les résultats ont révélé que 2831 formes de type ponctuel participent à la dégradation du cadre de vie. Ces formes sont principalement le fait des activités économiques informelles,
des points d’écoulement des eaux usées et des dépôts sauvage d’ordures. Quant aux formes d’expression surfaciques contribuant à la dégradation du cadre de vie, la végétation spontanée non entretenue et les espaces d’habitations ont été mis en cause. Celles-ci représentent respectivement 30,87 % et 28,67 % de l’aire totale du quartier. Les 40,06 % restant sont le fait de sol nu considéré comme neutre.
La spatialisation par carroyage des indices de la dégradation du cadre de vie indique les valeurs les plus importantes sont localisées dans les secteurs ou l’habitat est plus dense.
On en a conclu que la dégradation est induite par la pression produite par la densification du bâti et des effectifs de population.
Mot clés : dégradation, cadre de vie, urbanisation, cartographie, Cocody.
Introduction history, including propagule pressure and residence time, has been proposed as a primary driver of biological invasions. However, it is unclear whether introduction history increases the likelihood that a species will be invasive or only the likelihood that it will be established. Using a dataset of non‐native species historically available as ornamental plants in the conterminous United States, we investigated how introduction history relates to these stages of invasion. Introduction history was highly significant and a strong predictor of establishment, but only marginally significant and a poor predictor of invasive success. Propagule pressure predicted establishment better than residence time, with species likely to be established if they were introduced to only eight locations. These findings suggest that ongoing plant introductions will lead to widespread establishment but may not directly increase invasive success. Instead, other characteristics, like plant traits and local scale processes, may better predict whether a species becomes invasive.
Invasive alien species implications in ecological threats are attributed to their unique characteristics that are linked to their invasion. Veronica persica (Plantaginaceae family) is an alien weed species in Egypt. Regardless of its widespread globally in various regions, the growth traits and behavior of V. persica remain poorly understood. The comprehensive analysis, reveals the optimal germination (Gmax) was detected at 10/20 °C, 15/20 °C, and 20/25 °C at the moderate temperature regimes. The rapid germination rate (G rate) peaked at 10/20 °C regime, with a rate of 0.376 per day. Furthermore, under stress conditions, V. persica has 50% germination inhibition (G50) and 50% of growth inhibition occurred at − 0.91 MPa and 0.75 MPa of osmotic pressure and 3225.81 ppm and 2677.1 ppm of salt stress (NaCl) respectively. The germination ranged from 6 to 9 pH, with the highest germination percentage occurring at a pH of 7 & 8, reaching 88.75% compared to the control group. There is a strong interaction effect between habitats and plant stages, the plant stages and habitats have significant effects (p ≤ 0.00) on V. persica growth. There was high and moderate plasticity in the response of morphological and growth features between stages. During the seedling-juvenile interval and the juvenile-flowering stages, respectively, there was a noticeable increase in both Relative Growth Rate and Net Assimilation Rate. Demographic surveys identified approximately 24 species across 11 families associated with V. persica in invaded areas. The Sorenson indices of qualitative index exhibited high similarity values in the invaded sites by (82.35%) compared to (72.72%) in non-invaded sites. However, interactions with native communities were reflected in lower richness, diversity, and evenness, displaying slightly higher Simpson index 1 (λ) values compared to invaded and non-invaded sites (0.043 and 0.0290) vs. (0.0207 and 0.268), in rangelands and F. carica orchards respectively. These results emphasize the substantially higher adaptability of V. persica to variable environmental conditions and abilities to invade a new community. This knowledge about invasive V. persica weeds germination and growth is itemized as the consistent predictive base for future invasion and informs strategic management priorities.
Symphyotrichum squamatum (Spreng.) G.L.Nesom, a South American species, was first introduced to Europe in 1905 and has since become invasive in numerous countries. In Romania, it was first documented in Bucharest in 2015 and it has since spread to various urban and peri-urban areas. This study aims to assess the invasive potential of Symphyotrichum squamatum in Romania through a comprehensive approach that includes modeling the species’ potential distribution, evaluating its reproductive success, and analyzing morpho-structural characteristics of its vegetative body. Additionally, we compared the species’ traits with those of another alien species from the same genus, Symphyotrichum ciliatum (Ledeb.) G.L.Nesom, which is currently invasive in Romania, thereby demonstrating its potential for invasiveness. The potential distribution of both Symphyotrichum squamatum and Symphyotrichum ciliatum in Romania was modeled using the R software, with the SSDM package and environmental variables corresponding to the species’ ecological preferences, such as climatic variables, local topographic, pedological factors, and anthropogenic impact. Reproductive success of Symphyotrichum squamatum was assessed through germination tests on individuals from different populations. The modeling results suggested that Symphyotrichum squamatum ’ distribution in Romania is largely influenced by the anthropogenic impact index and soil classes. Furthermore, the high percentages obtained from germination tests, along with the structural characteristics which highlighted its ability to adapt to a wide range of environmental conditions, indicate that Symphyotrichum squamatum is a species with expansion potential if it establishes under favorable environmental conditions, primarily represented by wetlands along watercourses and marshy areas.
The ecological impacts of invasive alien species are well known, as are the large-scale economic losses caused by these species. Less well known are the impacts of these species on human
wellbeing. In developing countries, like India, where a large proportion of the population is rural and intricately dependent on natural resources for its sustenance, the impacts of invasive species
on people’s wellbeing are likely to be as important as their ecological impacts. In this paper, we undertake a qualitative review of the literature on impacts of invasive alien species, specifically
plants, on human wellbeing in India. Our results show that impacts are diverse across various aspects of wellbeing and are both positive or negative based on local contexts. This plurality is
indicative of the need for a more nuanced approach to impact analysis and stakeholder mapping. We use constituents of human wellbeing as outlined in the Socioeconomic Impact Classification
for Alien Taxa (SEICAT) and the Sustainable Livelihoods Framework (SLF) to analyze invasive plant impacts, identify knowledge gaps, and discuss recommendations for future research on
impacts of invasive species. Although the widespread natural resource dependency among rural, tribal, and other marginalized communities of India gives biological invasions a socioeconomic
dimension (due to impacts of invasion on these resources), the human and social dimensions of species invasions have been neglected compared to their ecological dimension. We suggest that
understanding the pluralities of wellbeing circumstances with invasive species could help improve policies for management of invasive species in India.
Invasive plants may alter ecological and ecosystem processes, including the N-cycle. The Fallopia species complex is a well-studied invasive species whose N-resource acquisition traits define it as an acquisitive species. However, the study of the impacts of invasive plants on the N-cycle never considers the N-acquisition strategy as a reference for choosing another suitable plant control. The purpose of this study is to assess the impacts of an invasive species (Fallopia japonica FJ) on the N-cycle and to compare with those caused by a native acquisitive species (Dactylis glomerata DG), all compared to unplanted soils. A four-months mesocosm experiment was conducted by growing FJ and DG on nine different soils and measuring their impacts on N-cycle microbial activities (free-living nitrogen fixation FLNF, denitrification DEA, nitrification NEA), on N-mineral forms and on functional N-cycle gene abundance (nifH, AOA, AOB, nirS, nirK) as well as the total bacterial community gene (rRNA 16S). The nine soils differ in microbial enzymatic activities, N-mineral form concentrations, physico-chemical factors, texture, and gene abundances. Plant effects on FLNF, NEA and DEA are only soil dependent and no effect of invasive status was found. In addition, the native plant DG generally affected microbial parameters over a wider range of soils than the invasive plant. Stronger impacts of the native DG on microbial gene abundances were found compared to the invasive FJ. A stronger effect of the invasive plant was found for the soil NO3− concentration, with a significant decrease under the FJ than under the DG. Under both FJ and DG, NH4+ concentrations were not significantly affected. In conclusion, the invasive status in the ecosystem of the two plants studied cannot be explained through their impacts on microbial enzymatic activities and gene abundances of the soil N-cycle and the soil N mineral pools.
https://authors.elsevier.com/a/1ixoh1R%7EeWaDg
Inventories of alien species are important for monitoring and understanding the dynamics of invasion, which is crucial in devising management policies. The present study prepared a comprehensive inventory of alien plant species in Pakistan. Based on field observations, published work, scientific reports and online databases, 400 alien taxa were identified (83 families, 265 genera), 180 of which were classified as casual alien, 117 as naturalized, and 103 as invasive. Poaceae (61 taxa) and Asteraceae (46 taxa) were the richest families, while Ipomoea (9), Amaranthus (8) and Euphorbia (8) were the genera with the largest numbers of alien taxa. The greater majority of alien species were annuals (32%) irrespective of their stage in the process of invasion. Alien species from all continents have invaded Pakistan but the primary donors of alien species are Temperate Asia (176) and Africa (143 species). Alien taxa inhabit all six geographic regions of Pakistan and the largest number (117) is found on the Punjab fertile plains. Ruderal habitats support a wide array of alien plant species, hosting almost all the alien species irrespective of their invasion status. The introduction pathway of the great majority of alien species remains unclear (67%) due to insufficient data on their history of introduction. Our account of the alien flora of Pakistan draws attention to further work needed and highlights the gaps that need to be addressed for devising a national alien species management strategy.
The distribution of four alien Reynoutria taxa (R. japonica var. japonica, R. japonica var. compacta, R. sachalinensis and R. x bohemica), native to East Asia, and history of their introduction to and spread in the Czech Republic was studied. The most widely distributed representative of the genus, R. japonica var. japonica, was first recorded in 1883 by A. Weidmann in cultivation in S Bohemia. The first record outside cultivation is from N Bohemia in 1902. Up to 2000, it has been recorded in 1335 localities, most frequently in riparian and human-made habitats. The dwarf variety R. japonica var. compacta is of a limited distribution that depends on rare cultivation and subsequent escape. The first herbarium specimen was collected in 1948 and the first record out of cultivation is from 1995. R. sachalinensis was recorded in 261 localities. It was first collected in 1921 in Central Bohemia. A herbarium specimen of a plant cultivated in the Botanical Garden of the Charles University in Prague, collected in 1950, has been re-determined as R. x bohemica, the hybrid between R. japonica var. japonica and R. sachalinensis, and represents the earliest record of the hybrid in the Czech Republic. Since then, this taxon was observed in 381 localities. Herbarium records were used to compare the rate of spread among the three common taxa in 1952-1995, i.e. since when the hybrid started to appear in herbaria. R. japonica var. japonica has been spreading significantly faster than R. sachalinensis and the hybrid exhibits twice the rate of invasion of its parents.
Data on 15 reserve characteristics were derived from surveys of 234 reserves. The most important characteristics influencing the number of problem weeds in reserves are proximity to towns, distance from roads and railway lines, human use, reserve shape, and habitat diversity. Reserves with the most weeds are narrow remnants on fertile soils with clearings and a history of modification, and those close to towns or sites of high human activity. -from Authors
No account of the effects of fire in mountain fynbos would be complete without considering invasive alien plants. Introduced plants are a striking feature of fynbos landscapes, and they have a marked effect on the functioning of natural ecosystems (Richardson et al. 1991).
Alien flora of the Czech Republic is presented. In Appendix 1, 1378 alien taxa (33.4% of the total flora) are listed with information on the taxonomic position, origin, invasive status (casual, naturalized, invasive; a new category post-invasive is introduced), time of immigration (archaeophytes vs. neophytes), habitat type invaded (natural, seminatural, human-made), vegetation invaded (expressed as occurence in phytosociological alliances), mode of introduction into the country (accidental, deliberate), and date of the first record. Number of phytogeographical as well as biological and ecological attributes were compiled for each species in the database; its structure is presented in Appendix 2 as a suggestion for similar work elsewhere. Czech alien flora consists of 24.1% of taxa which arrived before 1500 (archaeophytes) and 75.9% neophytes. There are 891 casuals, 397 naturalized and 90 invasive species. Of introduced neophytes, 21.9% became naturalized, and 6.6% invasive. Hybrids contribute with 13.3% to the total number of aliens, and the hybridization is more frequent in archaeophytes (18.7%) than in neophytes (11.7%). If the 184 hybrids are excluded from the total number of aliens, there are 270 archaeophytes and 924 neophytes in the Czech flora, i.e. total of 1195 taxa. Accidental arrivals account for 53.4% of all taxa and deliberate introduction for 46.6%; the ratio is reversed for neophytes considered separately (45.5 vs. 54.5%). Majority of aliens (62.8%) are confined to human-made habitats, 11.0% were recorded exclusively in natural or seminatural habitats, and 26.2% occur in both types of habitat. Archaeophytes and neophytes occur in 66 and 83 alliances, respectively, of the phytosociological system. Flora is further analysed with respect to origin, life histories, life forms and strategies. Only 310 species (22.4% of the total number of all alien taxa) are common or locally abundant; others are rare, based on a single locality or no longer present. The following 19 taxa are reported as new for the Czech alien flora: Agrostis scabra, Alhagi pseudalhagi, Allium atropurpureum, Bromus hordeaceus subsp. pseudothominii, Carduus tenuiflorus, Centaurea xgerstlaueri, Centaurea nigra x phrygia, Cerastium xmaureri, Gilia capitata, Helianthus strumosus, Hieracium pannosum, Hordeum leporinum, Oenothera coronifera, Papaver atlanticum subsp. mesatlanticum, Parietaria pennsylvanica, Polypogon fugax, Rodgersia aesculifolia, Sedum pallidum var. bithynicum, Sedum stoloniferum; these represent results of our own field research as well as of herbaria search, and unpublished data from colleagues. Other 44 taxa are reported as escaping from cultivation for the first time. Twenty two archaeophytes are listed in the Red List of the Czech flora.
We evaluated the effects of plant functional group richness on seasonal patterns of soil nitrogen and phosphorus cycling, using serpentine grassland in south San Jose, California. We established experimental plots with four functional types of plants: early-season annual forbs (E), late-season annual forbs (L), nitrogen-fixers (N), and perennial bunchgrasses (P). These groups differ in several traits relevant to nutrient cycling, including phenology, rooting depth, root:shoot ratio, size, and leaf C:N content. Two or three species of each group were planted in single functional group (SFG) treatments, and in two-, three-, and four-way combinations of functional groups. We analyzed available nutrient pool sizes, microbial biomass nitrogen and phosphorus, microbial nitrogen immobilization, nitrification rates, and leaching losses.
We used an index of “relative resource use” that incorporates the effects of plants on pool sizes of several depletable soil resources: inorganic nitrogen in all seasons, available phosphorus in all seasons, and water in the summer dry season. We found a significant positive relationship between increasing relative resource use (including both plant and microbial uptake) and increasing plant diversity. The increase in relative resource use results because different functional groups have their maximum effect on different resources in different seasons: E’s dominate reduction of inorganic nitrogen pools in winter; L’s have a stronger depletion of nitrogen in spring and a dominant reduction of water in summer; P’s have a stronger nitrogen depletion in summer; N-fixers provide additional nitrogen in all seasons and have a significant phosphorus depletion in all seasons except fall. Single functional group treatments varied greatly in relative resource use; for example, the resource use index for the L treatment is as high as in the more diverse treatments.
We expected a reduction of leaching losses as functional group richness increased because of differences in rooting depth and seasonal activity among these groups. However, measurements of nitrate in soil water leached below the rooting zone indicated that, apart from a strong reduction in losses in all vegetated treatments compared to the bare treatment, there were no effects of increasing plant diversity. While some single functional group treatments differed (P ≤ L, N), more diverse treatments did not. Early- and late-season annuals, but not perennial bunchgrasses, had significant positive effects on microbial immobilization of nitrogen in short-term (24 h) ¹⁵N experiments.
We conclude that: (1) total resource use, across many resource axes and including both plant and microbial effects, does increase with increasing plant diversity on a yearly timescale due to seasonal complementarity; (2) while the presence of vegetation has a large effect on ecosystem nitrogen retention, nitrogen leaching losses do not necessarily decrease with increasing functional group richness; (3) indirect effects of plants on microbial processes such as immobilization can equal or exceed direct effects of plant uptake on nutrient retention; and (4) plant composition (i.e., the identity of the groups present in treatments) in general explains much more about the measured nutrient cycling processes than does functional group richness alone (i.e., the number of groups present).
The expansion of Alliaria petiolata into a broadrange of habitats in New Jersey was examined by comparing demographic and reproductive characteristics in four habitats that differed in availability of moisture and light. Plants behaved as strict biennials in all sites in all years. Survivorship, seed weight, and seed germination were lower in the drier habitats. The timing of flowering was later (1-2 weeks) in the drier habitats, although it did not appear to affect fruit maturation (as estimated by fruit abortion) which occurred during the drier months in all sites. Fecundity as measured by seeds/ fruit and fruit production significantly differed among the populations although seeds/plant did not differ. Fruit abortion, which differed among the populations and among years, may be most influenced by environmental fluctuations rather than any characteristics intrinsic to the sites. The allocation of resources (biomass) to reproduction was greatest in the most disturbed site. A common garden experiment using seedlings from the two most contrasting sites suggested that variation in most traits (flowering phenology and resource allocation) was primarily a response to the environment. However, survivorship was more affected by seedling origin. This research suggests that A. petiolata responds to the broad range of habitats primarily by phenotypic plasticity. While A. petiolata had lower survivorship in the drier habitats, its phenotypic variation in demographic and reproductive characteristics may have allowed successful range expansion.
Ecosystem engineers are organisms that directly or indirectly modulate the availability of resources to other species, by causing physical state changes in biotic or abiotic materials. In so doing they modify, maintain and create habitats. Autogenic engineers (e.g. corals, or trees) change the environment via their own physical structures (i.e. their living and dead tissues). Allogenic engineers (e.g. woodpeckers, beavers) change the environment by transforming living or non-living materials from one physical state to another, via mechanical or other means. The direct provision of resources to other species, in the form of living or dead tissues is not engineering. Organisms act as engineers when they modulate the supply of a resource or resources other than themselves. We recognise and define five types of engineering and provide examples. Humans are allogenic engineers par excellence, and also mimic the behaviour of autogenic engineers, for example by constructing glasshouses. We explore related concepts including the notions of extended phenotypes and keystone species. Some (but not all) products of ecosystem engineering are extended phenotypes. Many (perhaps most) impacts of keystone species include not only trophic effects, but also engineers and engineering. Engineers differ in their impacts. The biggest effects are attributable to species with large per capita impacts, living at high densities, over large areas for a long time, giving rise to structures that persist for millennia and that modulate many resource flows (e.g. mima mounds created by fossorial rodents). The ephemeral nests constructed by small, passerine birds lie at the opposite end of this continuum. We provide a tentative research agenda for an exploration of the phenomenon of organisms as ecosystem engineers, and suggest that all habitats on earth support, and are influenced by, ecosystem engineers.
ABSTRACT Geographical differentiation of populations can be interpreted as a result of adaptive processes in response to environmental gradients and biotic interactions. Such adaptations are particularly interesting in invasive alien species which have been present in an area for a relatively short time. There are few observations of latitudinal trends in alien plants, and no account exists for Impatiens glandulifera, a problematic annual weed in most countries of central and north-western Europe. Here we describe variation in growth and phenology in 26 populations of this species from nine European regions in a common garden in Denmark. Above-ground biomass (an estimate of fecundity), height and basal diameter were lower in the northern populations which were first to produce flowers. Some differences were also observed in biomass allocation to leaves, flowers and fruits, albeit without a latitudinal pattern. The latitudinal trends in growth and survival disappeared in a field experiment, probably due to suboptimal site conditions. Most variation in plant traits was explained by differences among regions with some minor effects of populations within regions. Besides latitude, no other geographical, climatic or population trait correlated with the observed differences in growth and phenology. Differences in latitude may mainly represent variation in length of the growing season. The causes and potential consequences of such latitudinal trends for population dynamics and dispersal of alien plants are discussed.
ABSTRACT The traditional approach to understanding invasions has focused on properties of the invasive species and of the communities that are invaded. A well-established concept is that communities with higher species diversity should be more resistant to invaders. However, most recently published field data contradict this theory, finding instead that areas with high native plant diversity also have high exotic plant diversity. An alternative environment-based approach to understanding patterns of invasions assumes that native and exotic species respond similarly to environmental conditions, and thus predicts that they should have similar patterns of abundance and diversity. Establishment and growth of native and exotic species are predicted to vary in response to the interaction of plant growth rates with the frequency and intensity of mortality-causing disturbances. This theory distinguishes between the probability of establishment and the probability of dominance, predicting that establishment should be highest under unproductive and undisturbed conditions and also disturbed productive conditions. However, the probability of dominance by exotic species, and thus of potential negative impacts on diversity, is highest under productive conditions. The theory predicts that a change in disturbance regime can have opposite effects in environments with contrasting levels of productivity. Manipulation of productivity and disturbance provides opportunities for resource managers to influence the interactions among species, offering the potential to reduce or eliminate some types of invasive species.
ABSTRACT Introduced plant species that became successful invaders appear often more vigorous and taller than their conspecifics in the native range. Reasons postulated to explain this better performance in the introduced range include more favourable environmental conditions and release from natural enemies and pathogens. According to the Evolution of Increased Competitive Ability hypothesis (EICA hypothesis) there is a trade-off between investment into defence against herbivores and pathogens, and investment into a stronger competitive ability. In this study, we conducted field surveys to investigate whether populations of the invasive perennial Solidago gigantea Ait (Asteraceae) differ with respect to growth and size in the native and introduced range, respectively. We assessed size and morphological variation of 46 populations in the native North American range and 45 populations in the introduced European range. Despite considerable variation between populations within continents, there were pronounced differences between continents. The average population size, density and total plant biomass were larger in European than in American populations. Climatic differences and latitude explained only a small proportion of the total variation between the two continents. The results show that introduced plants can be very distinct in their growth form and size from conspecifics in the native range. The apparently better performance of this invasive species in Europe may be the result of changed selection pressures, as implied by the EICA hypothesis.
Concern over the consequences of species loss has generated tremendous interest in how species diversity affects ecosystem processes (Naeem et al. 1994; Tilman and Downing 1994; Chapin et al. 1998; Hector et al. 1999). Resistance to biological invasions has been a process of particular interest because exotic species are well documented to have large ecological and economic impacts (Mooney and Drake 1986; Drake and Mooney 1989; Vitousek et al. 1997). Furthermore, that diverse communities better resist biological invasions is a classic notion in ecology, credited to Elton (1958), but also implicit in island biogeography (MacArthur and Wilson 1967) and species packing (MacArthur 1970, 1972) theories. Recently, however, this commonly held notion has become controversial (Enserink 1999).
The application of new molecular technology has greatly increased our understanding of the role of chromosomal change in plant evolution. There is now a broad database on genome size variation within and among species and a wide array of nuclear and cytoplasmic genetic markers. There is a variety of literatures addressing this subject but much of it is scattered. This book created a contemporary synthesis of work in this area and addresses issues such as herogeneity, polyploidy, chromosomal rearrangements within species and phenotypic consequences of chromosome doubling.
The weed floras of tropical (Mexico City) and temperate (Bariloche City, Argentina) urbanizations are compared. At world level, under medium to strong disturbance, no relationships were found between latitude (L) and percentage of exotic plant species (PES) (94 censuses), but under low disturbance, there is a significant positive correlation between L and PES. For 23 Argentine provinces there is an inverse relation between the native/exotics ratio and latitude (between 22-54°S). Eurasian weeds are more successful in temperate countries while tropical weeds are more influential in warm countries. About 4% of the 260 000 species of nominated vascular plants have become international weeds due to commerce and transportation; 10% of the natives, in different floras, show marked colonizing abilities. If the present process of the mingling of floras continues, then the number of international potential future weeds may (conservatively) be 26 000 species. -from Author
The family Fabaceae (Leguminosae) is used as a starting point for creating a database of naturalized/invasive plant taxa in Taiwan, a Pacific island with very limited available information on plant invasions. A comprehensive list of naturalized Fabaceae, with background information on origin, habit, life form, and minimum residence time for most of the species is presented. This family is the second largest dicotyledon family in Taiwan, with non-native species accounting for one-sixth of the naturalized flora of this island: 54 naturalized species (approximately 23.8% of resident legume flora, including native and naturalized species) represent 34 genera (eleven exotic to Taiwan) and three subfamilies. Most of the naturalized taxa belong to the subfamily Papilionoideae, and the majority of them are herbaceous perennials with a minimum resident time ≥ 60 years. Among these naturalized species, two are listed among the world's worst weeds, and at least six of them are known as important environmental weeds in other parts of the world. Most of the naturalized legumes were introduced from the Neotropics, and a notable portion (at least 50%) of them was introduced deliberately for cultivation as forage or ornamentals. Naturalized legumes often exhibit different rates of spread within similar time frames. For example, Crotalaria zanzibarica is known from approximately 70 localities, while C. bialata is known from only three different localities even though both have the same minimum residence time of 69 years. Such differences suggest that different taxa have a different degree of invasiveness.
It has been suggested that more species have been successfully introduced to oceanic islands than to mainland regions. This suggestion has attracted considerable ecological interest and several theoretical mechanisms have been proposed. However, few data are available to test the hypotheses directly, and the pattern may simply result from many more species being transported to islands rather than mainland regions. Here I test this idea using data for global land birds and present evidence that introductions to islands have a higher probability of success than those to mainland regions. This difference between island and mainland landforms is not consistent among either taxonomic families or biogeographic regions. Instead, introduction attempts within the same biogeographic region have been significantly more successful than those that have occurred between two different biogeographic regions. Subsequently, the proportion of introduction attempts that have occurred within a single biogeographic region is thus a significant predictor of the observed variability in introduction success. I also show that the correlates of successful island introductions are probably different to those of successful mainland introductions.
Determining which biological traits enable a species to become invasive has been a major objective in invasion ecology [1-5]. Part of the theory relies on comparisons of large species sets; such studies attempt to identify the factors that contribute to the probability that a species will be introduced to a region [6] and become naturalized or invasive [7-9]. It has been shown that different factors are of different importance at particular stages of the invasion process [6, 10]. Recently, sophisticated data on alien floras from around the world have become available in the scientific literature [8, 11-16]. Some biological and ecological traits of invading species were identified as contributing to the success of invasive species, e.g., high fecundity [17], efficient dispersal [18], ability to utilize generalist mutualists [19], ability to evade specific natural enemies [20], small genome size [3], relative growth rate [5] or specific leaf area [5, 20].
A unique attribute of invaders is that they thrive in a country in which they did not evolve. In this chapter, I review the physiological, demographic and genetic attributes of invaders sensu stricto (excluding native weeds or colonists). When compared to similar native species, invaders often have features likely to endow them with higher relative fitness. However, the few available comparisons may constitute a biased sample. Attempts to generalize show that the invasive flora of a country is composed of a large array of plant types and that there are no attributes with which to characterize invaders in general. More specific approaches of invasions, centered on the invaders or the recipient habitats, are reviewed. The need for an approach combining ecolological and evolutionary features of habitats and introduced species is emphasized.
The flora of 96 rubbish dumps consisting of organic, inorganic and industrial wastes was studied in the Czech Republic. Some dumps contained toxic substances (heavy metals, chlorethylenes, phenols, polychlorinated biphenyls, oil hydrocarbons and biogas). Statistically significant factors explaining the number and proportional representation of native plant species, archaeophytes (introduced before 1500) and neophytes (introduced later) were determined. In total, 588 species of vascular plants were recorded, with archaeophytes (133 species) over-represented and native species (322 species) and neophytes (133 species) under-represented compared to their proportions in the national flora. Minimum adequate models were used to determine the effects of several factors on species numbers and proportions, independent of other factors. Dump area, human density in the region and altitude (non-significant only in archaeophytes) were correlated positively with species numbers. Dump age, expressed as time since dump establishment, interacted with the dump toxicity; species numbers increased with dump age on non-toxic dumps, whereas on toxic dumps no increase in numbers was noted. For neophytes, dump toxicity also interacted with human density; the increase in numbers of neophytes with human density is more pronounced on toxic than on non-toxic dumps. The variables measured failed to explain observed differences in proportional representation of native species, archaeophytes and neophytes. This suggests that the occurrence of species growing in such extreme habitats is driven overwhelmingly by factors such as anthropogenic disturbance. A possible explanation for the positive effect of altitude on species numbers on dumps is that the effect of heating of the deposited substrate by microbiological processes, documented by previous studies, overrides the effect of altitude which was shown repeatedly to have a negative effect on species richness. Neophyte distribution is driven by an interplay of factors distinct from those influencing the distribution of native species, namely toxicity and human density (the latter we interpret as a surrogate for propagule pressure). Their distribution on studied dumps is more restricted than that of native taxa and archaeophytes, and they are more limited by toxic substrata; more intensive propagule pressure is required for their establishment at dumps with higher toxicity levels.
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.
With increasing frequency, humans have transported species around the globe, leading to geographic homogenization of formerly distinct communities. This loss of uniqueness among communities, and its consequences, have become major concerns for conservation biologists (Soule 1990). Competition and predation from alien species, as well as the spread of introduced diseases are well-recognized factors contributing the decline and disappearance of unique native species. More recently, genetic homogenization has been recognized as an additional consequence of alien species introductions. Genetic homogenization, at a global scale, results from hybridization between native and introduced species or populations. Rhymer and Simberloff (1996) reviewed cases of hybridization between native and alien species and populations, emphasizing examples and consequences in a wide variety of animal taxa. This chapter focuses on hybridization between native and alien plant species and its implications for plant conservation. We consider a species alien when it is known to have been introduced to a given region from a different region of the world.
Tropical island ecosystems appear to be especially vulnerable to invasive species as indicated by the often high numbers and percentages of exotic species on oceanic and continental islands. Here I reexamine hypotheses offered to account for the apparently high invasibility of tropical islands and suggest a simple synthesis based on resource availability, propagule supply, and relative competitive abilities of exotic and island species. This review suggests that fundamentally two interacting processes-high net resource availability and poor ability of native species to preempt those resources-make island communities vulnerable to the establishment and spread of alien species. In addition, historically high rates of introduction have provided opportunity in the form of a diverse and abundant propagule rain of exotic species. The combination produces a scenario that is not an optimistic one for island ecosystems. It suggests that these native ecosystems on islands are particularly vulnerable to naturalizing exotics growing on their borders, and that while disturbance from a variety of causes, including pigs, fire, grazing, and natural dieback of the canopy dominants, increases the opportunities for exotic incursions, even intact forests are not immune. Unless these forests are aggressively managed and alien propagule pressure reduced, they will be highly modified by expanding exotic plant populations. Tropical islands are an effective early warning system of the impacts that successive waves of exotic species invasions may cause to isolated ecosystems. As mainland natural areas become fragmented, degraded and depauperate, they acquire many of the ecological attributes of islands, including limited habitat area, missing functional groups, declining species diversity, and disturbed habitats. A better understanding of invasions on islands may improve our attempts to protect both mainland and island ecosystems from the impacts of exotic species.
1. Human activity is an increasingly important mechanism of plant dispersal, particularly in densely populated countries such as England. We investigated which species are commonly dispersed by the following vectors: (i) soil carried on motor vehicles, (ii) topsoil, (iii) sugar factory topsoil, (iv) horticultural stock, and (v) garden throw-outs. 2. We compared the ecological traits of the species associated with each vector with those of a representative sample of the regional flora. Traits examined were life history, canopy height, lateral spread, flowering start, flowering period, seed persistence in the soil, vegetative reproduction, wind dispersal, log seed weight and specific leaf area. 3. We identified two major anthropogenic dispersal pathways, each associated with a clearly defined group of species. Species associated with topsoil, cars and horticulture depend essentially on soil movement, and are often small and fast-growing, but their most consistent unifying characteristic is the production of numerous, small, persistent seeds. In contrast, garden throw-outs, which are themselves functionally similar to increasing garden escapes, tend to be tall, spreading perennials with transient seed banks, attributes which are almost the exact opposite of the soil-borne group. 4. Some recent studies of the British flora have failed to find any dispersal-related differences between those species with increasing or decreasing ranges, or between natives and invasive aliens. Others have found contradictory attributes of aliens; they were more likely to have bigger seeds than natives, but also more likely to have a persistent seed bank. These findings are consistent with the suggestion that there exist two contrasting groups of successful alien invaders: tall, spreading competitors and small, short-lived, fast-growing species with high reproductive outputs. The parallel with the two groups of species identified here is remarkable, and is further evidence of the probable importance of anthropogenic dispersal in the modern landscape.
Models of plant migration based on estimates of biological parameters severely underestimate the rate of spread when compared to empirical estimates of plant migration rates. This is disturbing, since an ability to predict migration and colonization rates is needed for predicting how native species will distribute themselves in response to habitat loss and climate change and how rapidly invasive species will spread. Part of the problem is the difficulty of formally including rare long‐distance dispersal events in spread models. In this article, we explore the process of making predictions about plant migration rates. In particular, we examine the links between data, statistical models, and ecological predictions. We fit mixtures of Weibull distributions to several dispersal data sets and show that statistical and biological criteria for selecting the most appropriate statistical model conflict. Fitting a two‐component mixture model to the same data increases the spread‐rate prediction by an average factor of 4.5. Data limit our ability to fit more components. Using simulations, we show that a small proportion (0.001) of seeds moving long‐distances (1–10 km) can lead to an order of magnitude increase in predicted spread rate. The analysis also suggests that most existing data sets on dispersal will not resolve the problem; more effort needs to be devoted to collecting data on long‐distance dispersal. Although dispersal had the strongest effect on the predicted spread rate, we showed that dispersal interacts strongly with plant life history, disturbance, and habitat loss in influencing the predicted rate of spread. The importance of these interactions means that an approach that integrates local and long‐distance dispersal with plant life history, disturbance, and habitat availability is essential for predicting migration rates.
Experiments are described showing that most artificial autopolyploids derived from native or introduced perennial grass species from California are far inferior in behavior under field conditions than their diploid ancestors. In a single species, Ehrharta erecta in two out of 22 localities, the autotetraploid maintained itself for, respectively, 19 and 39 years, but remained either in the exact locality of planting or in nearby localities having very similar ecological conditions. The control diploids, direct descendants of the progenitors of the autopolyploids, spread more widely and evolved more variation with respect to growth habit among each progeny. These results, along with other evidence derived from several literature sources, strengthen the hypothesis that successful polyploids among natural populations are usually or almost always the result of increased heterozygosity accompanying either interracial or interspecific hybridization. The hypothesis that polyploids succeed because of their greater tolerance of severe ecological or climatic conditions is again rejected, and that which postulates secondary contacts between previously isolated populations as the principal cause for their high frequencies in some groups of angiosperms is favored. The unusually high frequency of polyploids in the Gramineae is attributed to the probable fact that habitats to which they are best adapted have changed in extent and position repeatedly during the geological periods since the initial evolution of the family.
Some theories and experimental studies suggest that areas of low plant species richness may be invaded more easily than areas of high plant species richness. We gathered nested-scale vegetation data on plant species richness, foliar cover, and frequency from 200 1-m2 subplots (20 1000-m2 modified-Whittaker plots) in the Colorado Rockies (USA), and 160 1-m2 subplots (16 1000-m2 plots) in the Central Grasslands in Colorado, Wyoming, South Dakota, and Minnesota (USA) to test the generality of this paradigm. At the 1-m2 scale, the paradigm was supported in four prairie types in the Central Grasslands, where exotic species richness declined with increasing plant species richness and cover. At the 1-m2 scale, five forest and meadow vegetation types in the Colorado Rockies contradicted the paradigm; exotic species richness increased with native-plant species richness and foliar cover. At the 1000-m2 plot scale (among vegetation types), 83% of the variance in exotic species richness in the Central Grasslands was explained by the total percentage of nitrogen in the soil and the cover of native plant species. In the Colorado Rockies, 69% of the variance in exotic species richness in 1000-m2 plots was explained by the number of native plant species and the total percentage of soil carbon. At landscape and biome scales, exotic species primarily invaded areas of high species richness in the four Central Grasslands sites and in the five Colorado Rockies vegetation types. For the nine vegetation types in both biomes, exotic species cover was positively correlated with mean foliar cover, mean soil percentage N, and the total number of exotic species. These patterns of invasibility depend on spatial scale, biome and vegetation type, spatial autocorrelation effects, availability of resources, and species-specific responses to grazing and other disturbances. We conclude that: (1) sites high in herbaceous foliar cover and soil fertility, and hot spots of plant diversity (and biodiversity), are invasible in many landscapes; and (2) this pattern may be more closely related to the degree resources are available in native plant communities, independent of species richness. Exotic plant invasions in rare habitats and distinctive plant communities pose a significant challenge to land managers and conservation biologists.
Impatiens glandulifera was estimated as having a rate of spread of up to 38 km yr-1, compared to a rate of up to 24 km yr-1 for I. parviflora. Impatiens capensis was also studied. The use of vice-county data as opposed to 10 km squares is discussed. To identify characters which enabled I. glandulifera to be so successful, frost tolerance and seed output seem to be important factors. Occasional long distance dispersal events, probably aided by humans, are considered to be responsible for the rapid spread of I. glandulifera. Impatiens glandulifera is a pest plant because it forms dense monospecific stands in damp woodland, swamping all other plants. It is able to do so because of early germination and rapid growth to a height higher than any other British annual. Local spread is limited to 2 m yr-1 from its own ballistic dispersal and to a small multiple of that from animal spread. -from Authors
Weed status in Australia was associated with being geographically widespread in southern Africa, being found in a wide range of climates in southern Africa, being described as a weed or targeted by herbicides in southern Africa, with early introduction and establishment in Australia, and with weediness in regions other than southern Africa. Multiple logistic regressions were used. The best fitting regressions were for weeds present for a long time in Australia (>140 yr). They utilized three variables, namely weed status, climatic range in southern Africa and the existence of congeneric weeds in southern Africa. The highest level of variation explained (43%) was obtained for agricultural weeds using a single variable, weed status in southern Africa. Being recorded as a weed in Australia was related to climatic range and the existence of congeneric weeds in southern Africa (40% of variation explained). Recently-arrived species which were predicted to become weeds are Acacia karroo (Mimosaceae), Arctotis venustra (Asteraceae), Sisymbrium thellungii (Brassicaceae) and Solanum retroflexum (Solanaceae). Analysis of the residuals of the regressions indicated two long-established species which might prove to be good targets for biological control: Mesembryanthemum crystallinum (Aizoaceae) and Watsonia meriana (Iridaceae). -from Authors
