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Plant traits and temporal scale: evidence from a 5-year invasion experiment using native species
Abstract
1A long-term experiment was established in 1990 in which seeds of 54 native species, not originally present at the site, were sown into a fertility × disturbance matrix established in unproductive limestone grassland at the Buxton Climate Change Impacts Laboratory (BCCIL). The objective was to examine the roles of productivity and disturbance as major factors controlling the invasibility of plant communities, and to identify the functional characteristics of successful invaders in response to different types of invasion opportunity. The results of the first 2 years of the study have already been published.2After 2 years, invasion was strongly promoted by disturbance and less so by increased fertility. Three years later the cover of invaders had declined over most of the matrix, and the greatest cover of sown species was where the highest levels of fertility and disturbance coincided. However, no part of the fertility–disturbance matrix was immune to invasion and the area of the matrix occupied by each of the sown species that successfully established was unique. Abundance of invaders was reduced by low soil pH.3The identity and distribution of the successful invaders changed as the early stages of invasion gave way to a later stage of consolidation. After 2 years regenerative traits (seed mass and germination characteristics) were the best predictors of success. After 5 years these traits were unrelated to success of the invaders, the most successful invaders were perennial grasses, and no single trait was a good predictor of invasiveness.4Our results are consistent with the hypothesis that invasions are promoted by an increase in the availability of resources, either through addition of extra resources or a reduction in their use by the resident vegetation.
... Several studies have tried to identify traits defining a successful colonizer but a review of these studies has highlighted some contradictions (see Pyšek & Richardson, 2007). This lack of consistency can partly be explained by interactions between different traits (Küster, Kühn, Bruelheide, & Klotz, 2008), by trait dissimilarity to resident species being more important for establishment success than specific traits values (Feng et al., 2018;Loiola et al., 2018), and by different traits values being advantageous at different stages of colonization or in different environments (Crawley, Harvey, & Purvis, 1996;Kempel et al., 2013;Van Kleunen, Dawson, & Maurel, 2015;Thompson, Hodgson, Grime, & Burke, 2001). Hence, different studies, both experimental and observational, might provide partially contrasting results. ...
... In addition to plant properties determining the outcome of colonization, environmental conditions such as nutrient availability, can modify ecosystem processes by affecting plant-plant interactions and community saturation. For instance Lepš (2014) showed that 15 years of fertilization in a central European oligotrophic meadow, led to increased competition between plants and species richness depletion by exclusion of subordinate species.In terms of colonization, lower nutrient availability was found to reduce establishment of colonizers (Fargione & Tilman, 2005) while higher levels of nitrate in the soil was found to increase the total abundance of colonizers in resident plant communities (Knops et al., 1999;Roscher et al., 2009;Thompson et al., 2001). ...
... Our analyses based on colonizing species' functional traits support observations made by previous studies, i.e. a shift in traits characterizing successful colonizers along successional phases of the colonization process: initial colonizers are replaced by species with different traits (Catford et al., 2019;Roscher et al., 2015;Thompson et al., 2001). In the first year after establishment, annual colonizers with therophytic life form, high SLA and low LDMC were relatively abundant, although no significant difference in abundance was detected TA B L E 2 Effect of the functional and phylogenetic structure of the resident community on resistance to colonization. ...
Functional and phylogenetic diversity (FD and PD respectively) of the resident community are expected to exert a key role in community resistance to colonization by surrounding species, and their establishment success. However, few studies have explored this topic experimentally or evaluated the interactive effects of these diversity measures.
We implemented a diversity experiment to disentangle the role of FD and PD by sowing mixtures of 6 species, drawn from a pool of 19 species naturally coexisting in central European mesic meadows. The mixtures were designed to cover four independent combinations of high and low FD and PD. Species covers were estimated in spring and late summer over two growing seasons. We then assessed the establishment success of colonizers as a function of their mean traits and phylogenetic distance to the resident (i.e. sown) communities, as well as the resistance of the resident communities to natural colonizers as a function of their functional and phylogenetic structure.
Results generally indicated a temporal shift regarding which trait values made a colonizer successful, from an acquisitive strategy in early stages to a more conservative trait syndrome in later stages.
FD decreased community resistance to natural colonization. However, PD tempered this effect: with high PD, FD was not significant, suggesting complementary information between these two components of biodiversity. On average, colonizing species were more functionally distant from the resident species in sown communities with high functional diversity, i.e. those that were more colonized.
Synthesis. Our results confirm an interplay between FD and PD during community assembly processes, namely resistance to colonizers, suggesting that these two descriptors of biodiversity only partially overlap in their contribution to the overall ecological structure of a community. The hypothesis that higher FD increases resistance through a more complete use of resources was challenged. Results rather suggested that greater FD could provide an unsaturated functional trait space allowing functionally unique species to occupy it.
... diversity) could arise depending on the factor, or set of factors, driving the disassembly process ( Zavaleta et al. 2009). Such community patterns may be depicted by shifts in abundance of native and exotic functional groups, reflecting differential species' responses to major environmental gradients ( Thompson et al. 2001;Chaneton et al. 2002;Huston 2004;Besaw et al. 2011). For instance, short-lived ruderal forbs are expected to thrive under disturbed, resource-rich conditions ( Grime 2001), whereas legumes would be favoured in N-poor soils ( Ritchie & Tilman 1995). ...
... Invasion may be also promoted by increased resource supply ( Burke & Grime 1996;Daehler 2003), provided there is sufficient delay in the uptake of extra resources by resident plants ( Shea & Chesson 2002). Moreover, the magnitude of invasion should be highest under the combined effects of disturbances and resource pulses ( Davis, Grime & Thompson 2000;Thompson et al. 2001). This implies that community invasibility is not static but fluctuates over time ( Davis & Pelsor 2001;Melbourne et al. 2007), a condition that should be common to grassland remnants ( Leach & Givnish 1996;Wiens 2009). ...
... This protocol augmented N supply rates, simulating anthropogenic inputs from cattle waste, fertilizer run-off and atmospheric deposition (Pi~ neiro, Paruelo & Oesterheld 2006). Overall, treatments were designed to alter resource availability through periodic reductions in the light intercepted by established plants and by pulsed addition of a limiting soil nutrient ( Davis, Grime & Thompson 2000;Thompson et al. 2001). D A T A C O L L E C T I O N We examined the effects of mowing and N addition on post-burn community dynamics during 2004-2007. ...
1. Native vegetation fragments embedded in anthropogenic landscapes are increasingly threatened by land-use intensification. Managing disturbance regimes and nutrient inputs may help maintain species diversity in such remnants. Yet it is unclear the extent to which changes in resource availability due to reduced capture by resident plants and/or increased supply rates may trigger native community disassembly and exotic invasions.2. We examined how mowing disturbance and N fertilizer addition affected plant community recovery after a burning event in a remnant corridor of tussock pampa grassland in Argentina. The percentage cover and richness of native and exotic plant functional groups were monitored over four years. According to the ‘fluctuating resource theory’, we expected invasion to be highest when both light and N availability were increased simultaneously.3. Mowing delayed recovery by dominant C4 tussock grasses and promoted subordinate, native C3 grasses and exotic legumes, thus enhancing both native and exotic species richness. Fertilization induced a transient increase in native forbs but decreased total plant richness. Moreover, N addition to mowed grassland led to rapid invasion by short-lived exotic forbs, which were then replaced by exotic perennial grasses. Exotic grasses eventually spread across the grassland corridor, although at different rates depending on the treatment, and in parallel to a generalized decline in native species cover.4. Synthesis and applications. Community disassembly patterns reflected differential responses of native and exotic functional groups to altered resource supply rates. Synergisms between canopy disturbances and N enrichment posed the greatest threat to preserving a pampa grassland remnant prone to invasion. Establishing buffer zones may be required to enhance the viability of corridor-like grassland remnants in agricultural landscapes.This article is protected by copyright. All rights reserved.
... However, in disturbed habitats, such as agricultural habitats, different species traits contribute to the success of alien species under different disturbance types (Pyšek et al. 1995, Lake and Leishman 2004). Although species traits of a successful invader are known to vary according to the habitat type and environmental conditions, the interaction has largely been ignored in the empirical studies in quest of species traits in successful plant invasions (but seeThompson et al. 2001, Lake and Leishman 2004, Lososová et al. 2006, Thuiller et al. 2006, Pyšek et al. 2009b). ...
... Although agricultural habitats are among the most invaded habitats (e.g.Lonsdale 1999, Pyšek et al. 2010a), the studies of the temporal, spatial and within-habitat variation in the invasion level of alien plants in agricultural habitats are lacking. In addition the factors contributing to the invasion level have been studied insufficiently (but seeThompson et al. 2001, Lake and Leishman 2004, Leishman and Thompson 2005, Thuiller et al. 2006), especially in the boreal region. Species vary in their response to environmental conditions (e.g.Richardson and Pyšek 2006) and in their effect on native species diversity (e.g.Stohlgren et al. 1999). ...
... Grime also initiated impressive experiments on plant communities outdoors, notably on the controls limiting invasion by species not naturally present (Thompson et al., 2001) Grubb, 1980) and at greater length (as nobody else could bring themselves to do it), in my chapter in White (1985). By the time I wrote my paper on three basic and strikingly different strategies of plants which cope with shortages of resources (Grubb, 1998), I related my three types to Grime's one because readers were familiar with his system, but I was no longer primarily directing my comments against the CSR scheme, and had a lot more positive new things to say. ...
Perhaps as much as any other scientist in the 20th century, J.P. Grime transformed the study of plant ecology and helped shepherd the field toward international prominence as a nexus of ideas related to global environmental change. Editors at the Journal of Ecology asked a group of senior plant ecologists to comment on Grime's scientific legacy.
This commentary piece includes individual responses of 14 scientists from around the world attesting to Grime's foundational role in plant functional ecology, including his knack for sparking controversy, his unique approach to theory formulation involving clever experiments and standardized trait measurements of large numbers of species, and the continued impact of his work on ecological science and policy.
... For example, soil pH may influence the distribution of alien plants, because soil pH affects nutrient availability (Bigelow and Canham 2002). Several studies have shown that alien plants are less abundant in areas with high soil acidity (Thompson et al. 2001;Collette andPither 2015, but Ender et al. 2017). However, there are only a few studies of the relationship between the distribution of alien plants and soil pH (e.g., Dyderski and Jagodziński 2019a, b), and therefore the role of soil pH as a barrier to the invasion of alien plants deserves further investigation (Teo et al. 2003). ...
Invasion of alien plant species can have irreversible effects on ecosystems. Although alien plants often distribute in disturbed area, understanding of the initial invasion process soon after disturbance is poor. We compared forest floor vegetation between thinning treatment plots and intact control plots in a red pine (Pinus densiflora) forest in central Japan to test whether the thinning treatment (i.e. disturbance) induced invasion of alien plants. We also examined how invasion of aliens is influenced by the environment, plant traits, and buried seeds in the soil. In control plots, few alien plants emerged at the herbaceous layer and only a few buried seeds of alien plants were found. In treatment plots, on the other hand, many alien plants were observed both at the herbaceous layer and in the soil seed bank. Treatment plots had a larger percentage of canopy openness than control plots. In treatment plots, the cover of alien plants was negatively correlated with the distance from the nearest primary road. Alien plants had taller maximum plant height, larger leaves, and greater leaf nitrogen concentration than native species in treatment plots. This indicates that alien plants were superior to native plants in growth, competition, and carbon assimilation abilities. Alien plants tended to have seeds with long dispersal abilities, such as anemochory and zoochory, and short life histories, such as annual and biennial histories. These findings suggest that thinning promoted invasion of alien plants and that alien plants had the potential for further invasion by rapid dispersion, establishment, and growth.
... Regenerative traits have an evident influence on the expansion rate of exotic species in a new environment (Thompson et al. 2001;Tecco et al. 2012). For this reason, the study of the germination responses of A. dealbata to different factors leads to a better understanding of its autoecology and provides knowledge for development of management strategies. ...
Ecological theory predicts that the success of exotic plants in new environments depends on a combination of ecological attributes. Requirements for germination and seedling traits are the main components in the regenerative niche, and largely determine the success of exotic species in a new environment. Acacia dealbata Link is an Australian species with a great invasive potential. In Chaco Mountains (central Argentina), it seems to be undergoing a lag phase, as some local dominance in the form of dense monospecific patches has been recorded, although restricted to few disperse populations. In the present study we assessed which functional traits would allow this global invader to successfully overcome its lag phase, and what conditions could benefit or limit this process. Imbibition and germination experiments were designed, and included four temperature regimes in light and in continuous darkness. Additionally, germination response to light quality and simulation fire experiment was also conducted. Further, soil samples were taken to determine the size of the soil seed bank, and a morpho-functional characterisation of seedlings was conducted. Despite the absence of a consistent fire-stimulated germination response, our findings were in line with generalist germination requirements. Physical seed dormancy, large seed bank, broad temperature and light germination requirements, and fast-growing seedlings make this species a potential invader in this mountain system, and suggest that these regenerative attributes might help A. dealbata to overcome its present lag phase. Findings show that the efficiency of management decreases and the related economic cost increases as the time since invasion increases, so early intervention will be key in preventing spread of this species thorough this mountain region.
... It is possible that this introduced bias toward earlier-germinating plants in our study. These first germinants, however, likely represent a major portion of the trait variation in established seedlings in the field (e.g., Thompson et al., 2001;James et al., 2006). Plants were fertilized weekly after individuals produced two true leaves (Peter's 20-20-20 solution, Scotts Miracle-Gro). ...
Premise of Study
Mechanisms by which invasive species succeed across multiple novel environmental contexts are poorly understood. Functional traits show promise for identifying such mechanisms, yet we lack knowledge of which functional traits are critical for success and how they vary across invaded ranges and with environmental features. We evaluated the widespread recent invasion of Sahara mustard (Brassica tournefortii) in the southwestern United States to understand the extent of functional trait variation across the invaded range and how such variation is related to spatial and climatic gradients.
Methods
We used a common garden approach, growing two generations of plants in controlled conditions sourced from 10 locations across the invaded range. We measured variation within and among populations in phenological, morphological, and physiological traits, as well as performance.
Key Results
We found nine key traits that varied among populations. These traits were related to phenology and early growth strategies, such as the timing of germination and flowering, as well as relative allocation of biomass to reproduction and individual seed mass. Trait variation was related most strongly to variation in winter precipitation patterns across localities, though variations in temperature and latitude also had significant contributions.
Conclusions
Our results identify key functional traits of this invasive species that showed significant variation among introduced populations across a broad geographic and climatic range. Further, trait variation among populations was strongly related to key climatic variables, which suggests that population divergence in these traits may explain the successful colonization of Sahara mustard across its invaded US range.
... Bottom-up controls are those that emphasize the application of properties and processes that contribute to the resilience and resistance of the invaded community (McEvoy and Coombs 1999). Often invasive plant management can enhance invasibility through resource release and decreased competition (Thompson et al. 2001;Minchinton and Bertness 2003), resulting in the reinvasion of the plant targeted for control or the colonization by a new invasive plant (Kettenring and Adams 2011). Frequent surface fire may act as a long-term topdown control strategy for managing Chinese tallow and may also drive bottom-up community processes. ...
Biological invasions by woody species in forested ecosystems can have significant impacts on forest management and conservation. We designed and tested several management options based on the physiology of Chinese tallow (Triadica sebifera [L.] Small). Specifically, we tested four treatments, including mastication, foliar herbicide, and fire (MH fol F), mastication and foliar herbicide (MH fol), dormant-stem herbicide and fire (H dor F), and dormant-stem herbicide (H dor), to determine their efficacy in reducing the density and regeneration of this highly invasive tree species. Mastication treatments were significant in reducing density the first year but not after 3 years. Prescribed fire significantly reduced density combined with previous treatments. Regeneration coverage was highest on those sites with mastication, which was not affected by the addition of prescribed fire. Overall, we found that the most comprehensive treatment (MH fol F) was more effective in reducing density but did not result in a difference in the amount of regeneration after treatment.
... In present study, a pH range between 4 and 6 was obtained, which confirms that the soil was acidic. This has also been known to hamper plant development (Thompson et al., 2001). Notwithstanding, the pH range in the study; soils impacted with lower concentrations of the pesticides had lower pH values compared to higher pesticide concentrations at specific times. ...
The present study investigated growth performance of Eleusine indica to abiotic stress occasioned by
pesticide pollution with a view to ascertaining its suitability for phytoremediation. Soil was spiked with 2,2-
dichlorovinyl dimethyl phosphate (DDVP, 1000EC) in solution to obtain 6 different levels of pollution: 5.0,
3.75, 2.5, 0.5, 0.25, and 0.05 ml pesticide/kg of soil. The control was wetted with ordinary water. These
treatments were replicated 3 times in completely randomized block design. The entire set up was left to
naturally attenuate for 2 days before equal-lengthen 3-leaf tillers of Eleusine indica, the test plant, were
transplanted from a nursery. Results showed that within 24 h, young tillers in the 5 ml/kg-soil treatment
wilted entirely. Those in 2.5 – 5.0 ml/kg pesticide-impacted soil (PIS) also showed wilting signs, beginning
first with folding of plant leaves. There was no evidence of wilting in plants sown in the 0.05 ml/kg PIS and
the control. Total pesticide residual content after 11 weeks was 0.512 mg/kg in the 5 ml/kg-PIS (i.e. 10.24%
reduction) that lacked plant presence (note, plants died during the first few days). However, Residual content
ranged from 0.012 – 0.073 mg/kg in the treatments with plant presence, thus indicating the importance of
plant presence. Remediation efficiency was 13.60 – 29.20% in treatments with surviving plant population.
Eleusine indica grass showed great promise as a phytoremediator of pesticide. However, the fact that
significant morphological changes occurred in the plant also goes to show the effects of increased
concentrations of contaminants on the would-be phytoremediators.
... For example, nitrogen often limits productivity (Fenn et al. 1998, Bedford et al. 1999), but human-induced nitrogen availability has increased exponentially since the 1950s (Vitousek et al. 1997, Fixen and West 2002, Galloway et al. 2003) and now accounts for 45% of all nitrogen fixed globally ( Canfield et al. 2010). Ecologists have long known that nutrient enrichment can enhance the relative abundance of one or a few highly productive species (Tilman 1987, Carson and Barrett 1988, Carson and Pickett 1990, Goldberg and Miller 1990, Rajaniemi 2002, Lamb et al. 2009, Isbell et al. 2013), and within the context of plant invasions, introduced species can often increase in abundance due to nutrient enrichment ( Huenneke et al. 1990, Thompson et al. 2001, Leishman and Thomson 2005. If strong bottom-up effects from nutrient enrichment outweigh the effects of top-down suppression by biocontrol agents (e.g., by increasing an invader's tolerance of or resistance to herbivory), then nutrient enrichment alone may enhance invasiveness and thwart biocontrol success. ...
The degree to which biocontrol agents impact invasive plants varies widely across landscapes, often for unknown reasons. Understanding this variability can help optimize invasive species management while also informing our understanding of trophic linkages. To address these issues, we tested three hypotheses with contrasting predictions regarding the likelihood of biocontrol success. (1) The biocontrol effort hypothesis: invasive populations are regulated primarily by top-down effects, predicting that increased biocontrol efforts alone (e.g., more individuals of a given biocontrol agent or more time since agent release) will enhance biocontrol success. (2) The relative fertility hypothesis: invasive populations are regulated primarily by bottom-up effects, predicting that nutrient enrichment will increase dominance by invasives and thus reduce biocontrol success, regardless of biocontrol efforts. (3) The fertility-dependent biocontrol effort hypothesis: top-down effects will only regulate invasive populations if bottom-up effects are weak. It predicts that greater biocontrol efforts will increase biocontrol success, but only in low-nutrient sites. To test these hypotheses, we surveyed 46 sites across three states with prior releases of Galerucella beetles, the most common biocontrol agents used against invasive purple loosestrife (Lythrum salicaria).
We found strong support for the fertility-dependent biocontrol effort hypothesis, as biocontrol success occurred most often with greater biocontrol efforts, but only in low-fertility sites. This result held for early stage metrics of biocontrol success (higher Galerucella abundance) and ultimate biocontrol outcomes (decreased loosestrife plant size and abundance). Presence of the invasive grass Phalaris arundinacea was also inversely related to loosestrife abundance, suggesting that biocontrol-based reductions in loosestrife made secondary invasion by P. arundinacea more likely.
Our data suggest that low-nutrient sites be prioritized for loosestrife biocontrol and that future monitoring account for variation in site fertility or work to mitigate it. We introduce a new framework that integrates our findings with conflicting patterns previously reported from other biocontrol systems, proposing a unimodal relationship whereby nutrient availability enhances biocontrol success in low-nutrient sites but hampers it in high-nutrient sites. Our results represent one of the first examples of biocontrol success depending on site fertility, which has the potential to inform biocontrol-based management decisions across entire regions and among contrasting systems.
... In experiments, invasiveness correlated to plant traits and invasibility to resource availability ( Milbau et al. 2003) or standing biomass ( Troumbis et al. 2002). Trait composition of successful invaders may change during a successional series (Thompson et al. 2001). ...
... Despite the fact that physical space is not a consumable resource (McConnaughay and Bazzaz, 1991;Bazzaz, 1996), its effects on the access to other resources such as water, nutrients, and light could play an important role in determining the outcomes of resource competition between alien and native species. The majority of studies referring to space constraints have examined patterns of invasions following disturbances creating gaps (increases in light availability) that can be colonized by ruderal invaders (e.g., D'Antonio and Vitousek, 1992;Hobbs and Huenneke, 1992;Thompson et al., 2001;Buckley et al., 2007), while the effects of space on competitive interactions between invasive and native species represent a major research need (Gao et al., 2014) that requires further investigation. ...
Invasions by alien plants provide a unique opportunity to examine competitive interactions among plants. While resource competition has long been regarded as a major mechanism responsible for successful invasions, given a well-known capacity for many invaders to become dominant and reduce plant diversity in the invaded communities, few studies have measured resource competition directly or have assessed its importance relative to that of other mechanisms, at different stages of an invasion process. Here, we review evidence comparing the competitive ability of invasive species vs. that of co-occurring native plants, along a range of environmental gradients, showing that many invasive species have a superior competitive ability over native species, although invasive congeners are not necessarily competitively superior over native congeners, nor are alien dominants are better competitors than native dominants. We discuss how the outcomes of competition depend on a number of factors, such as the heterogeneous distribution of resources, the stage of the invasion process, as well as phenotypic plasticity and evolutionary adaptation, which may result in increased or decreased competitive ability in both invasive and native species. Competitive advantages of invasive species over natives are often transient and only important at the early stages of an invasion process. It remains unclear how important resource competition is relative to other mechanisms (competition avoidance via phenological differences, niche differentiation in space associated with phylogenetic distance, recruitment and dispersal limitation, indirect competition, and allelopathy). Finally, we identify the conceptual and methodological issues characterizing competition studies in plant invasions, and we discuss future research needs, including examination of resource competition dynamics and the impact of global environmental change on competitive interactions between invasive and native species.
... Since heterogeneity contributes to ecosystem stability (Frank and McNaughton 1991), the more homogenous vegetation in lantana-invaded sites was relatively unstable and, hence, disturbed compared to uninvaded sites. The disturbed vegetation may, in turn, alter resource availability and create conditions suitable for invasion (Thompson et al. 2001). The depletion of useful plant species also causes economic loss to local forest dwellers. ...
Lantana camara, an aromatic shrub, native to tropical America, was introduced into India for ornamental hedging, but later escaped and became a serious invasive weed. This study assessed the quantitative and qualitative status of plant community richness and diversity in areas invaded by L. camara in the Siwalik Hills (Himachal Pradesh, India), and explored allelopathy as a possible mechanism of interference. We measured species diversity, richness and evenness of the vegetation in areas invaded and uninvaded by L. camara. Allelopathic effects of L. camara rhizosphere soil and litter were assessed against two native plants-Achyranthes aspera (a herb) and Albizia lebbeck (a tree). Density, biomass and indices of diversity, richness and evenness were reduced by L. camara, indicating a significant alteration in composition and structure of native communities. Seedling growth of the test species was reduced in L. camara rhizosphere- and litter-amended soil. The inhibitory effect was ameliorated by the addition of activated charcoal, indicating the presence of organic inhibitors (quantified as phenolics) in the soil. Lantana invasion greatly reduces the density and diversity of the vegetation in the invaded area, and chemical interference of its litter plays an important role in invasion.
... This suggests that many species of ancient grasslands are severely limited in dispersal ability, and thus have a very low probability of reaching isolated sites unaided ( Pywell et al. 2003;Violle et al. 2007;Ozinga et al. 2009;Marini et al. 2012). Previous studies have demonstrated that traits determining colonization ability are most influential at the earlier stages of grassland regeneration on ex-arable land, with traits associated with tolerance of local conditions becoming increasingly important over time ( Thompson et al. 2001;Pywell et al. 2003). Consequently, the largest differences in dispersal ability were between Lost, Recent and Mid age grasslands. ...
QuestionsWhat is the time-scale for natural regeneration of calcareous grassland? Is this time-scale the same for individual plant species, plant community composition and functional traits? LocationDefence Training Estate Salisbury Plain, Wiltshire, UK. Methods
We investigated the rate of natural regeneration of species-rich calcareous grassland across a 20 000-ha landscape. We combined a large-scale botanical survey with historic land-use data (6–150 yrs before present) and examined differences between grassland age classes in the occurrence of individual plant species, plant community composition and plant community functional traits. ResultsMany species showed a significant association with grasslands over 100 yrs old. These included the majority of those defined elsewhere as calcareous grassland indicators, although some appeared on grasslands <10 yrs old. Plant community composition showed increasing similarity to the oldest grasslands with increased grassland age, with the exception of very recently ex-agricultural grasslands. Most functional traits showed clear trends with grassland age, with dispersal ability differing most strongly between recent and older grasslands, whilst soil fertility and pH tolerance were more influential over longer time-scales. Conclusions
Even in a well connected landscape, natural regeneration to a community resembling ancient calcareous grassland in terms of functional traits and plant community composition takes over a century, although changes at the level of individual species may occur much earlier. These findings confirm the uniqueness of ancient calcareous grassland. They also suggest that the targets of re-establishment efforts should be adjusted to account for the likely time-scale of full community re-assembly.
... In future, it is recommended that landfills are capped with nutrient-poor soils and that natural colonisation is used in combination with appropriate management (mowing and the removal of clippings) to reduce the build-up of nutrients and prevent the dominance of competitive species, thereby potentially leading to the development of species-rich grassland (Marrs & Gough, 1989;Olff, Berendse, & Visser, 1994;Walker et al., 2004). Plant colonisation is governed by both dispersal limitation, which determines the potential species pool, and the ability of species to establish and persist Thompson, Hodgson, Grime, & Burke, 2001). Ideally, to achieve any degree of success, sites should be within the potential dispersal distances of target grassland species for restoration and, if not, seed addition may have to be used to overcome dispersal limitation ( Pywell et al., 2002). ...
Biodiversity conservation through restoring degraded habitats or creating new habitats is advocated in the UK Biodiversity Action Plan. Restored grasslands on capped landfill sites are semi-natural habitats that could potentially support a wide range of plant communities. However, it is unknown whether these re-created habitats represent a significant resource in terms of biodiversity conservation. The UK National Vegetation Classification (NVC) was used to study these communities on nine restored capped landfill sites together with paired reference sites in the East Midlands region of the UK during 2007. Plant species data were collected by random quadrats along two 100 m transects from each site. The effects of restoration were investigated by examining plant attributes and Ellenberg indicators on restored landfill sites in comparison to paired reference sites. A total of 170 plant species were found from both sets of sites. There were no significant differences for most of the plant attributes between restored landfill sites and reference sites, though reference sites had significantly higher mean frequencies of native plants, nationally decreasing species and perennial species. In total 26 broad NVC community types were identified of which more than 70% fell within mesotrophic grassland (MG). The diversity of NVC communities confirms that underlying environmental factors such as soil fertility are important, dictating the type of plant communities that exist. It is recommended that management of these capped landfill sites should be targeted towards specific NVC community types to meet conservation targets.
John Philip ‘Phil’ Grime developed fundamental theory in plant ecology that emerged from a lifetime of fieldwork and experimental studies in the Sheffield region, South Yorkshire, UK. His approach was an unusual combination of observation, experiment and theory: he conducted detailed, intensive observations of natural communities, alongside experimental manipulation of those communities and simulated ‘microcosms’ in the service of formulating general rules (‘strategies’) by which plants evolve with respect to their environment. In this way, Grime was one of several key figures that propelled plant ecology away from descriptive methods focusing on vegetation composition and toward a science more integrated with other fields, including evolutionary biology and Earth science. Grime's investigative approach was an inspiration for the modern field of global change biology, and, by focusing on understanding the contrasting roles species and their traits play in the functioning of ecosystems, marked the beginning of the field of plant functional ecology. For much of his career Grime held the post of full professor (and in retirement, emeritus professor of ecology) at the University of Sheffield, where he also served as the director of the Unit of Comparative Plant Ecology and of the Buxton Climate Change Impacts Laboratory. Awarded an honorary doctorate by Radboud University (Nijmegen, The Netherlands) and a foreign membership of the Royal Netherlands Academy of Arts and Sciences, Grime was the first person awarded the Alexander von Humboldt Award of the International Association for Vegetation Science.
Current restoration protocols for roadside cut slopes in South Korea involve hydroseeding with exotic species to achieve early greening and soil stabilization. However, exotic species can negatively affect adjacent native ecosystems. This study investigated the functional traits of early colonizers in slope restoration and surrounding environments to inform restoration methods that generate similar communities as those of native ecosystems. Slope vegetation (species density, species cover, upperstory species, canopy cover) and environment (aspect, angle, soil properties) were surveyed from the road edge to the forest boundary, and were classified as three distinct zones: a hydroseeded slope, a transition zone, and the forest edge. Naturally occurring species were classified into functional groups to examine dominant traits during early colonization. Hemicryptophyte or geophyte forest species and forest interior woody species were well established and dominant in transition zones and cut slopes. Potential native species for slope restoration can be identified by examining functional group species in the adjacent forest. These native species can achieve restoration goals and block invasive species in the same functional group. Festuca arundinacea (tall fescue), which is reported as an invasive alien species, rapidly spread after introduction for restoration. Thus, continuous monitoring for impact on native communities is required after sowing invasive alien species. Future slope restoration should consider native woody species and perennial forest sedge species that develop rhizomes, and reconsider the use of tall fescue. This study indicates that cut slopes can be appropriately managed to enhance the quality of habitats for native species.
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Exotic plant invasion can alter native soil microbial community composition, and further influence the biogeochemical processes. Little information is available about the impacts of the invasion chronosequence of Spartina alterniflora on the dynamics of soil microbial community. Soil microbial community in coastal salt marshes invaded by S. alterniflora and reference wetlands covered by Suaeda salsa were investigated using phospholipid fatty acids (PLFAs) profiling along a short-term chronosequence (i.e., 2-, 5- and 10-year) of S. alterniflora invasion in the Yellow River Estuary. Results exhibited an increase in soil moisture, soil organic matter (SOM), soil dissolved organic carbon (DOC), total nitrogen (TN) and the total of PLFAs with increasing invasion ages of S. alterniflora in these coastal salt marshes. Comparatively, soil pH and bulk density exhibited a weak decline along the invasion chronosequence. The elevated values of relative abundance of fungi and the ratios of fungi: bacteria (F/B) in all invaded salt marshes were mainly associated with the accumulation of soil available substrate (e.g., SOM, DOC and TN). S. alterniflora invasion also increased the ratios of gram-positive/gram-negative (G+/G-) bacterial PLFAs, with the highest value occurring in the 2-year invaded salt marshes. The bacterial stress indicated by ratios of cy17:0/16:1ω7c and cy19:0/18:1ω7c consistently decreased along the invasion chronosequence. In conclusion, the shifts of soil microbial community composition were tightly associated with soil variables, such as soil pH and soil nutrient supply. Our findings reflect the short-term chronological effects of S. alterniflora invasion on the soil physicochemical characteristics and microbial communities, which contributes to the linkage between the plant invasion and soil development of coastal salt marshes.
The extrinsic determinants hypothesis emphasizes the essential role of environmental heterogeneity in species’ colonization. Consequently, high resident species diversity can increase community susceptibility to colonizations because good habitats may support more species that are functionally similar to colonizers. On the other hand, colonization success is also likely to depend on species traits. We tested the relative importance of environmental characteristics and species traits in determining colonization success using census data of 587 vascular plant species collected about 70 yr apart from 471 islands in the archipelago of SW Finland. More specifically, we explored potential new colonization as a function of island properties (e.g. location, area, habitat diversity, number of resident species per unit area), species traits (e.g. plant height, life‐form, dispersal vector, Ellenberg indicator values, association with human impact), and species’ historical distributions (number of inhabited islands, nearest occurrence). Island properties and species’ historical distributions were more effective than plant traits in explaining colonization outcomes. Contrary to the extrinsic determinants hypothesis, colonization success was neither associated with resident species diversity nor habitat diversity per se, although colonization was lowest on sparsely vegetated islands. Our findings lead us to propose that while plant traits related to dispersal and establishment may enhance colonization, predictions of plant colonizations primarily require understanding of habitat properties and species’ historical distributions.
Most people can readily identify a forest, or a grassland, or a wetland - these are the simple labels we give different plant communities. The aim of this book is to move beyond these simple descriptions to investigate the 'hidden' structure of vegetation, asking questions such as how do species in a community persist over time? What prevents the strongest species from taking over? And, are there rules that confer stability and produce repeatable patterns? Answers to these questions are fundamental to community ecology, and for the successful management of the world's varied ecosystems, many of which are currently under threat. In addition to reviewing and synthesising our current knowledge of species interactions and community assembly, this book also seeks to offer a different viewpoint - to challenge the reader, and to stimulate ecologists to think differently about plant communities and the processes that shape them. © J. Bastow Wilson, Andrew D. Q. Agnew and Stephen H. Roxburgh 2019.
The savanna biome is one of the least invaded among global biomes, although the mechanisms underpinning its resistance to alien species relative to other biomes is not well understood. Invaders generally are at the resource acquisitive end of functional global plant trait variation and in low-resource savanna environments we might expect that successful invaders will only outperform native species under resource rich or highly disturbed conditions. However, invaders may also directly exploit resource stressed environments using resource conservative traits in some situations. It’s also possible that successful invaders and native species largely overlap in their trait profiles indicating site specific environmental factors are responsible for invader success in particular contexts rather than a general trait and functional divergence between invaders and native species. To address these various hypotheses, we compared a suite of morphological and physiological traits in graminoid and herbaceous native and co-occurring invasive plant species across a range of habitats in savannas of the Kimberley region of northern Australia. Invader grass species had traits associated with resource acquisition and fast growth rates, such as high SLA and leaf nutrient contents. In contrast, dominant native perennial grasses had traits characteristic of resource conservation and slow growth in resource stressed conditions. Trait profiles among invasive forbs and legumes exhibited stress tolerant traits relative to their native counterparts. Invaders also displayed strong divergence in reproductive traits, suggesting diverse responses to disturbance not indicated by leaf economic traits alone. These results suggest that savannas may be resistant to invaders with resource acquisitive traits due to their strong resource limitation.
Adaptive plastic responses in invasive species allow for establishment and persistence despite the lack of genetic matching to new environments. The capacity of annual species to invade habitats to which they are not adapted is likely to be predicated on post-invasion seed trait variation correlated with conditions in the new habitat. To test this, I compared variation in seed traits and germination patterns of Aegilops triuncialis , an invasive annual grass, from 69 sample populations from 24 sites in California (USA) across 13 years. Seed mass, germination fractions, seed viability, and strength of induced dormancy between dimorphic seed pairs were used to investigate plastic variation within and among populations, across two general soil types, and among two widespread maternal genotypes. I found that seed mass variation was constrained although both seed types showed a 3-fold range among populations, 20–25% variation within populations between years, and was positively correlated with longer growing seasons. However, induced seed dormancy in the small seed type was correlated with large seed mass and to late-season precipitation, suggesting that longer growing seasons influence the strength of maternal and sibling chemical signals that induce dormancy in the small seeds. Thus variation in small seed germination fractions varies with the growing conditions experienced by the maternal plant. The greater longevity of the small seed type suggests that plasticity in germination in this species may contribute to seed bank formation, which is atypical of invasive annual grasses in California, and this may contribute to the persistence and spread of A. triuncialis in invaded ranges.
Established populations of nonnative plant species occur in most ecosystems. The ecological effects of these invaders can vary from benign to substantial, while management perspectives on them range from beneficial to harmful. In this chapter we focus on those nonnative plant species considered ‘harmful’, defined here as having an ecological and/or economic impact undesirable to management and they are typical targets of management and restoration actions. For information on animal invaders, see Simberloff and Rejmanek (2010). Harmful invaders have been variously referred to as “invasive” (Mack et al. 2000) or “transformer” plant species (Richardson et al. 2000). While there is some management concern over rapidly spreading native species (Carey et al. 2012), we use the term invasive in the sense of Richardson et al. (2000): nonnative (alien, nonindigenous or exotic) species with the potential for rapid population growth. In many cases ecological impacts of the species have not been measured. Within a restoration context, we assume invasive species would be a target when they (1) already dominate a restoration site or its seedbank and are difficult to remove, (2) may leave behind legacies after removal, or (3) could invade a restoration site and co-opt the direction of postdisturbance/restoration succession by interfering with desired species.
Herbert Baker arguably initiated the search for species characteristics determining alien plant invasion success, with his formulation of the ‘ideal weed’. Today, a profusion of studies has tested a myriad of traits for their importance in explaining success of alien plants, but the multiple, not always appropriate, approaches used have led to some confusion and criticism. We argue that a greater understanding of the characteristics explaining alien plant success requires a refined approach that respects the multistage, multiscale nature of the invasion process. We present a schema of questions we can ask regarding the success of alien species, with the answering of one question in the schema being conditional on the answer of preceding questions (thus acknowledging the nested nature of invasion stages). For each question, we identify traits and attributes of species we believe are likely to be most important in explaining species success, and we make predictions as to how we expect successful aliens to differ from natives and from unsuccessful aliens in their characteristics. We organize the findings of empirical studies according to the questions in our schema that they have addressed, to assess the extent to which they support our predictions. We believe that research on plant traits of alien species has already told us a lot about why some alien species become successful after introduction. However, if we ask the right questions at the appropriate scale and use appropriate comparators, research on traits may tell us whether they are really important or not, and if so under which conditions.
The riparian zones have been for millennia a fundamental element for the settlement of the population due to the availability of water, the existence of meadows and fertile valleys as roads. Its ecological importance and their livelihood, however, have not prevented its degradation. For centuries this degradation has been gradual and slow, exponentially increasing from the twentieth century by human transformation capabilities of the medium. In mountain areas, the less human presence, coupled with an abrupt relief, a more hostile climate and lower agricultural potential, have allowed a better conservation of rivers, in morphological and biological aspects. However, in middle and lower zones, the degradation has been intense and it is increasingly difficult to find a riparian zone with its original and unaltered riparian vegetation. The main causes of riparian zones degradation are the agriculture on the floodplain, large hydraulic pipes, diversions and dams, channels that have destroyed and altered their morphology, biological and hydrological function. The rapid urban expansion in the riparian zones, in recent years, have caused the channelling of rivers to prevent flooding of building areas. The degradation of riparian zones join to undesirable presence of the exotic species, which will replace the native vegetation in these zones eventually. The riverbanks act as the last refuge of natural vegetation, but it has been replaced by agricultural crops or forest plantations. This situation presents a unique duality: the widespread degradation of the riverbanks and, at the same time, their high ecological value as stronghold for natural vegetation for wildlife and their role as biological corridors. In Mediterranean riparian habitats, uncontrolled presence of invasive and exotic species can reduce native plant species richness, which would be devastating for our environments. Based on the historical management, there are very limited control options available. The presence of weeds or exotic species in riparian zones creates controversial because these species invade very sensitive habitats. In this context, we suggest a methodology to address the management and control of one of the most invasive riparian weeds in the world, the grass Arundo donax L. (Giant reed), from an integrated perspective, improving the ecological status of the riparian zones and producing the less impact on the biodiversity. We combined mechanical, physical, chemical and biological techniques in a management programme of riparian zones, taking account the ecological factors of plant communities and social context. The findings of this research project should encourage further studies on the integrated management of invasive weeds in riparian zones, and environmental conditions that may influence field efficacy.
In coastal China, the exotic invasive Spartina alterniflora is preventing the establishment of native mangroves. The use of exotic species, control of exotic plant invasion, and restoration of native plant communities are timely research issues. We used exotic Sonneratia apetala Buch.-Ham and S. caseolaris (L.) Engl. to control invasive Spartina alterniflora Loisel through replacement control for five years, which concurrently promoted the restoration of native mangroves. This process includes three stages. I: In a mangrove area invaded by S. alterniflora, exotic S. apetala and S. caseolaris grew rapidly due to their relatively fast-growing character and an allelopathic effect. II: Fast-growing S. apetala and S. caseolaris eradicate S. alterniflora through shading and allelopathy. III: The growth of native mangrove was promoted because exotic plant seedlings cannot regenerate in the understory shade, whereas native mesophytic mangrove plants seedlings can grow; when the area experiences extreme low temperatures in winter or at other times, S. apetala dies, and native mangrove species grow to restore the communities. This model has important implications for addressing the worldwide problems of "how to implement the ecological control of invasion using exotic species" and "how to concurrently promote native community restoration during the control of exotic invasion".
Aims Functional traits are supposed to play an important role in determining the colonization success of new species into established
communities. Short-term experimental studies have documented higher resistance of more diverse grasslands against colonization
by new species. However, little is known about which traits colonizers should have to successfully invade diverse plant communities
in the longer term and how community history may modify the resistance of diverse communities against colonization.
Herbert Baker arguably initiated the search for species characteristics determining alien plant invasion success, with his formulation of the 'ideal weed'. Today, a profusion of studies have tested a myriad of traits for their importance in explaining success of alien plants, but the multiple, not always appropriate, approaches used have led to some confusion, and criticism. We argue that a greater understanding of the characteristics explaining alien plant success requires a refined approach that respects the multi-stage, multi-scale nature of the invasion process. We present a schema of questions we can ask regarding the success of alien species, with the answering of one question in the schema being conditional on the answer of preceding questions (thus acknowledging the nested nature of invasion stages). For each question, we identify traits and attributes of species we believe are likely to be most important in explaining species success, and we make predictions as to how we expect successful aliens to differ from natives and from unsuccessful aliens in their characteristics. We organize the findings of empirical studies according to the questions in our schema that they have addressed, to assess the extent to which they support our predictions. We believe that research on plant traits of alien species has already told us a lot about why some alien species become successful after introduction. However, if we ask the right questions at the appropriate scale and use appropriate comparators, research on traits may tell us whether they are really important or not, and if so under which conditions. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Non‐native invasive species ( NNIS ) are a global issue whose introduction into novel ecosystems can fundamentally alter nutrient recycling and storage. It is therefore important to understand factors that affect the abundance and distribution of NNIS and their effects on ecosystems.
We investigated how nutrient enrichment and herbivorous armoured catfish separately and in combination affect ecosystem processes in a subtropical spring‐fed river (San Marcos, River, TX, U.S.A.). A replicated stream channel experiment in which nutrient enrichment was cross‐classified with the presence and the absence of armoured catfish was conducted to evaluate how nutrient enrichment may affect the ecosystem and nutrient cycling effects of catfish.
The presence of catfish reduced periphyton biomass and altered detrital decomposition rates and, contrary to predictions, decreased periphyton N:P. In addition, the presence of catfish increased the severity of periphyton P‐limitation. We found little evidence that adding nutrients altered the effects of armoured catfish on ecosystem dynamics.
Armoured catfish likely play an important role in the nutrient dynamics of the San Marcos River, but nutrient enrichment has little influence on determining the magnitude of ecosystem and nutrient cycling effects of this invasive and stoichiometrically unique consumer.
The history of coal mining in South Poland has left a legacy of many spoil heaps across the landscape. These have presented the opportunity to study their colonisation and spontaneous successional sequences over a long time period. We use the plant functional group (PFG) approach to characterize and compare species diversity on spoil heaps of different ages by uti-lising the ecological characteristics (PFG categories) of the species recorded during the course of spontaneous vegetation development. By changing species frequency into functional group frequency it was possible to find the significant differences in the functional composition of the studied vegetation and to analyze the dataset using non-parametric statistics. There was a small increase in the number of species over time, while the frequency of geophytes, nanophanerophytes and megaphanerophytes increased significantly. A significant increase was also recorded for the frequency of competitors, stress-tolera-tors and stress-tolerant competitors and for native spe-cies. We found that the significant differences in species composition measured as PFG diversity occurred be-tween the youngest and the oldest age classes. The PFG approach provided valuable insights into the nature of the species composition of the developing vegetation on hard-coal mine spoil heaps. We suggest that it could be usefully applied in restoration practice in the future by facilitating the natural colonization of native species adapted to local conditions and thus retaining the local gene pool in these areas.
Resource competition theory suggests that the nature of diversity–resource–invasibility interactions will vary along fertility gradients, concurrent with changes in the relative availability of limiting above- versus below-ground resources. Experimental support for this contingency is lacking. Here, we manipulated resident diversity, baseline fertility, and the availabilities of light and soil nitrogen in grassland communities invaded by two functionally distinct non-native plant species (Lolium
arundinaceum and Melilotus alba). We tested the hypotheses that increased resident diversity reduces community invasibility and dampens the effects of light and soil nitrogen pulses, and that the relative effects of light versus soil nitrogen additions on diversity–invasibility relationships depend on the baseline fertility of the study system. Our results reveal an overall weak negative effect of resident diversity on Lolium performance, but in contrast to our expectations, this diversity effect did not vary with light or soil nitrogen additions or with baseline fertility. However, the relative effects of above- versus below-ground resource additions on invader performance varied with baseline fertility as expected: Lolium responded most strongly to soil nitrogen additions in low-fertility mesocosms and most strongly to increased light availability in high-fertility mesocosms. In contrast to Lolium, nitrogen-fixing Melilotus was overall less responsive to diversity and resource manipulations. Together, these patterns do not lend support for the dependence of diversity–resource–invasibility relationships on either baseline fertility or invasive species identity, but they do highlight the dominant role of resources over diversity in determining invader performance, as well as the manner in which fertility alters the relative importance of above- versus below-ground resource pulses in promoting invasions.
How does germination and establishment of non‐resident plant species differ among major types of wetland ecosystems in boreal forest landscapes? We evaluated the invasibility of three boreal‐forest wetland types by sowing seeds of six species from the native species pool and followed germination and survival for 3 yr. All species were able to invade all wetland types, suggesting all ecosystems were invasible, and that observed differences in invasion are due to differences in propagule pressure.
Las especies invasoras, como Phragmites australis, resultan grandes competidoras para las especies nativas; sin embargo,
es poco lo que se conoce sobre el mecanismo de invasión. En este trabajo se evaluó la interacción de P. australis con una
especie nativa, Schoenoplectus americanus, mediante un experimento de parcelas divididas con adición de nutrimento (nitrógeno
y fósforo). Para P. australis se encontraron diferencias (P < 0.05) entre tratamientos para la altura, el número de tallos y la biomasa
aérea y de rizomas, mientras que para S. americanus se encontraron diferencias (P < 0.05) en la altura máxima, la altura
promedio de tallos, el número de tallos, el porcentaje de cobertura y la biomasa aérea. El incremento de nutrimentos no permitió
que P. australis desplazara a S. americanus, lo que sugiere que en condiciones naturales S. americanus será capaz de competir por
los nutrimentos siempre y cuando no se presente algún disturbio, ya que en este estudio se mantuvo el dosel de especies nativas
antes de introducir a P. australis. Los resultados sugieren que la competencia intraespecífi ca es más fuerte que la interespecífi ca
en ausencia de disturbio.
Some ecologists and environmentalists have asked whether existing plant invaders could be used as sources of lignocellulosic ethanol, as an alternative to the introduction of potentially invasive non-native energy crops. Although the idea is tempting and could theoretically motivate the control or eradication of large invasive populations, we recognize that a number of major economic, logistic, and legal barriers currently prevent adoption of this plan. Here, we enumerate these barriers in detail, but conclude with an idealistic vision for the role of invasive biomass in the bioenergy industry.
Ecological theory predicts that the success of exotic plants in new environments depends on a combination of both regenerative and vegetative attributes. Identifying those attributes may benefit from approaches that specifically compare related exotic and native species, thereby overcoming strong habitat dependence and phylogenetic bias. Gleditsia triacanthos L. (Fabaceae) is described as an aggressive woody invader in a broad range of ecosystems of Argentina, where it coexists with other leguminous trees. In the present study, we assessed whether the success of G. triacanthos in the lower areas of Chaco woodlands of central Argentina is determined (1) by differences from the dominant native, Prosopis alba, in its combination of several attributes that enhance the invader's competitive ability, (2) by differences from P. alba in few key attributes that facilitate its spread, or (3) by strong functional similarities in response to environmental filtering by the invaded system. Our comparison of 19 functional traits of both species showed that regenerative and vegetative trends may vary independently, and that two contrasting strategies seem to underlie the success of G. triacanthos in this region. On the one hand, the invader might benefit by sharing regenerative attributes with the native relative that dominates the community, which is evidently a successful way of recruiting in the system. On the other hand, as recruitment is ensured, the species differs in several vegetative attributes, which may enhance its competitive ability in terms of growth rates and nutrient uptake.
Common reed (Phragmites australis) has invaded wetlands worldwide and displaced native vegetation and wildlife. Control measures include herbicides, but their use can cause negative environmental impacts. An alternative is to harvest aerial biomass. We tested harvest as a control for common reed in Mintzita springs, Michoacán in Western Mexico. Results showed that harvest increased native plant species establishment, and that species richness varied with harvesting method. In plots where reed was completely removed every two months, 9 native species established, the same number as in plots where all reed biomass was removed if at least one stem was 2 m tall at the harvest date. When only reed stems 2m or taller where removed, 6 species established, whereas, in control plots only three species established. Species composition correlated with harvesting method (ANOSIM, R=0.4514, p < 0.01). Harvest reduced resprouting measured as standing biomass (F(3,20) = 27, p < 0.000001). After one year of treatment, full removal plots had the lowest aerial dry biomass (108 ± 15 g) followed by plots with full removal once a reed stem was at least 2m tall (197 ± 81 g), followed by plots where only 2 m or taller stems were removed (593 ± 466 g) and control (3296 ± 232 g). Several reed plants died after the first year of the experiment. Although more trials and long term follow up are needed, our results suggest that harvest can be an efficient control method for reed-infested wetlands in Western Mexico.
Seedling growth rates can have important long-term effects on forest dynamics. Environmental variables such as light availability
and edaphic factors can exert a strong influence on seedling growth. In the wild, seedlings of Wollemi pine (Wollemia nobilis) grow on very acid soils (pH ∼4.3) in deeply shaded sites (∼3 % full sunlight). To examine the relative influences of these
two factors on the growth of young W. nobilis seedlings, we conducted a glasshouse experiment growing seedlings at two soil pH levels (4.5 and 6.5) under three light levels:
low (5 % full sun), medium (15 %) and high (50 %). Stem length and stem diameter were measured, stem number and branch number
were counted, and chlorophyll and carotenoid content were analysed. In general, increased plant growth was associated with
increased light, and with low pH irrespective of light treatment, and pigment content was higher at low pH. Maximum stem growth
occurred in plants grown in the low pH/high light treatment combination. However, stem number was highest in low pH/medium
light. We hypothesize that these differences in stem development of W. nobilis among light treatments were due to this species' different recruitment strategies in response to light: greater stem growth
at high light and greater investment in multiple stem production at low light. The low light levels in the W. nobilis habitat may be a key limitation on stem growth and hence W. nobilis recruitment from seedling to adult. Light and soil pH are two key factors in the growth of this threatened relictual rainforest
species.
Significance
In ecosystems worldwide, the presence of overabundant ungulates (e.g. deer, cows) and the invasion of exotic plants are disrupting native communities. A recent hypothesis causally links these problems implicating overabundant ungulates in enhancing invaders’ demographic success. We tested this hypothesis in a forest where white-tailed deer are overabundant and garlic mustard is aggressively invading. Using long-term, replicated deer exclusion/deer access plot pairs, we quantified population density, growth, and decline of this invader and native plants. We conclusively demonstrate that deer are required for garlic mustard success; its local extinction is projected where deer are absent. Our findings provide the first definitive support connecting overabundant ungulates to enhanced invader success, with broad implications for biodiversity and ecosystem function.
Disturbance may alter the resistance of communities to non-indigenous species as it frees space and removes competitively superior species. In a factorial field experiment we studied how different types of mechanical disturbance affected the biomass level of the non-indigenous amphipod Gammarus tigrinus in a brackish water charophyte community. Mechanical disturbance affected the biomass of G. tigrinus with a time lag between disturbance and response of the gammarid species. In general, all types of disturbance reduced gammarid biomasses. The effect persisted until the end of the experiment regardless of the recovery of macrophyte communities in terms of species number and biomass of benthic invertebrate and plant species. Thus, a possible cause of reduced biomass of the gammarid amphipods relates to the decreased biomass of Chara aspera and its structural changes. This indicates that the dominance of G. tigrinus in a low saline system has less to do with strong species interactions (e.g. competitive displacement) than with habitat-level processes (e.g. changes in habitat structural characteristics and food supply).
Positive species interactions have been shown to occur in a variety of plant systems, and the importance of these interactions is expected to vary with resource availability and abiotic stress. The processes by which these types of relationships operate and influence plant communities in coastal environments, however, are not fully understood. Positive species interactions were observed in areas of St. George Island, Florida, shortly after transplanting dune species for a restoration experiment designed to encourage the growth of foredune, interdune, and backdune vegetation. The dune habitats in St. George are subject to abiotic stresses that vary in type and magnitude, and the environmental factors responsible for ameliorating these conditions and encouraging positive vegetation change operate differently across these areas. We (1) investigated if transplants encouraged positive changes in vegetation across dune habitats, (2) determined whether disturbance (through transplanting) played a role, and (3) tested environmental factors involved in positive interactions to explain the changes in vegetation observed across dune habitats. The presence of transplants positively modified vegetation (e.g., species richness or cover) across all dune habitats. Experimental disturbance had no strong overall positive effect on vegetation change. Shading and soil moisture redistribution had differential effects on vegetation change among habitats, suggesting that these environmental factors interact with the abiotic characteristics unique to each dune habitat in complex ways. Our results suggest that experimentation over a longer time scale might be required to fully understand the extent at which positive interactions affect vegetation patterns along stressful environmental gradients.
The Forest Health Monitoring (FHM) Program’s annual national technical report has three objectives: (1) to present forest health status and trends from a national or a multi-State regional perspective using a variety of sources, (2) to introduce new techniques for analyzing forest health data, and (3) to report results of recently completed evaluation monitoring projects funded through the FHM national program. The first section of the report, which addresses the first two objectives, is organized according to the Criteria and Indicators for the Conservation and Sustainable Management of Temperate and Boreal Forests. A new phylogenetic approach is described for assessing the health of forest communities from an evolutionary perspective. Also depicted are new tools that allow the public to retrieve high-resolution maps of land cover patterns for specific locations. A methodology is described for the comparison of moisture conditions between different geographical areas and time periods. Aerial survey data are used to identify hotspots of insect and disease activity based on the relative exposure to defoliation and mortality-causing agents. Satellite data are employed to detect geographic clusters of forest fire occurrence. Forest Inventory and Analysis data from 17 States are employed to detect regional differences in tree mortality. Phytopthora kernoviae is described as a developing threat to forest health, and a national map of P. kernoviae establishment risk is presented. Soil quality indicator data are analyzed to determine regional trends in soil chemistry characteristics that play an important role in the growth of forest trees. Finally, annual change in woody carbon stocks is presented in an initial assessment of down woody material carbon flux in the North Central United States. In the second section of the report, seven recently completed evaluation monitoring projects are summarized, addressing a variety of forest health concerns at smaller scales. These projects include an evaluation of exotic plant invasion vulnerability in Pennsylvania, a description of black ash decline in Minnesota, an assessment of white pine blister rust in Washington State, an evaluation of alder dieback impact on ecosystem nitrogen balance in Alaska, an assessment of the impact of Swiss needle cast on Douglas-fir in Oregon, an examination of the effect of Minnesota winter temperatures on eastern larch beetle, and an evaluation of native bunchgrass communities in Oregon and Idaho following fire.
This paper examines the hypothesis that non-native plant invasions are related to fluctuating resource availability as proposed by Davis et al. (2000). I measured relative functional responses of both invasive and native plants to changed resource availability due to nutrient enrichment and rainfall, and to increased disturbance. Data are presented from studies in two contrasting ecosystems. First is a series of glasshouse and field experiments on the invader Hieracium lepidulum and associated invasive and native species in subalpine temperate New Zealand. Second is a field study of invasive and native plant responses to altered disturbance regimes and rainfall from tropical savannas of north eastern Australia. Invaders responded differently from native species to changes in resource availability in both subalpine and tropical studies. However, invaders differed among themselves showing that different species exploit different functional niches to invade their respective habitats. These findings contribute to the contention that the fluctuating resource hypothesis does not provide a universal explanation for plant invasions. The diverse functional responses to increased resource availability among invaders in this and previous studies suggest that the cause of invasion depends on unique combinations of habitat and functional attributes of invaders and native assemblages. Such findings imply that universal predictions of what will happen under climate change scenarios across the globe will be difficult to make.
Members of the balloon vine genus, Cardiospermum, have been extensively moved around the globe as medicinal and horticultural species, two of which are now widespread invasive species; C. grandiflorum and C. halicacabum. A third species, C. corindum, may also have significant invasion potential. However, in some regions the native status of these species is not clear, hampering management. For example, in South Africa it is unknown whether C. halicacabum and C. corindum are native, and this is a major constraint to on-going biological control programmes against invasive C. grandiflorum. We review the geography, biology and ecology of selected members of the genus with an emphasis on the two most widespread invaders, C. halicacabum and C. grandiflorum. Specifically, we use molecular data to reconstruct a phylogeny of the group in order to shed light on the native ranges of C. halicacabum and C. corindum in southern Africa. Phylogenetic analyses indicate that southern African accessions of these species are closely related to South American taxa indicating human-mediated introduction and/or natural long distance dispersal. Then, on a global scale we use species distribution modelling to predict potential suitable climate regions where these species are currently absent. Native range data were used to test the accuracy with which bioclimatic modelling can identify the known invasive ranges of these species. Results show that Cardiospermum species have potential to spread further in already invaded or introduced regions in Australia, Africa and Asia, underlining the importance of resolving taxonomic uncertainties for future management efforts. Bioclimatic modelling predicts Australia to have highly favourable environmental conditions for C. corindum and therefore vigilance against this species should be high. Species distribution modelling showed that native range data over fit predicted suitable ranges, and that factors other than climate influence establishment potential. This review opens the door to better understand the global biogeography of the genus Cardiospermum, with direct implications for management, while also highlighting gaps in current research.
Although the problem of plant invasions is expected to increase with climate change, there is as yet little experimental evidence, in particular, for the effects of extreme weather events. We established communities of European meadow species, which were subjected to warming and extreme event (drought and deluge) treatments in a factorial design at an experimental garden in Zurich, Switzerland. Phylogenetically matched pairs of native and alien species (Bromus erectus, B. inermis, Trifolium pratense,
T. hybridum,
Lactuca serriola, and Conyza canadensis) were introduced into the communities to test if invader performance is favored by warming and extreme events, and if alien invaders perform better than native colonizers. With a warming of on average 0.3 °C, a higher cover of native plant communities was observed, while drought decreased cover in the short-term and lowered biomass. Germination, survival, and growth of the introduced species were lower under elevated temperature. Survival of all pairs and growth of Trifolium was greater in drought pots, while deluge had no effect. While the alien species showed a faster rate of increase in the number of leaves, mortality of alien species was greater than of native species. Overall, the performance of the focal species varied much more among taxonomic groups than native/alien provenances. The results suggest that with climate change, different types of extreme events will differ in the severity of their effects on native plant communities. Meanwhile, the effects of climate change on plant invasions are more likely to operate indirectly through the impacts on native vegetation.
Although invasion risk is expected to increase with propagule pressure (PP), it is unclear whether PP-invasibility relationships follow an asymptotic or some other non-linear form and whether such relationships vary with underlying environmental conditions. Using manipulations of PP, soil fertility and disturbance, we tested how each influence PP-invasibility relationships for Lespedeza cuneata in a Kansas grassland and use recruitment curve models to determine how safe sites may contribute to plant invasions. After three growing seasons, we found that the PP-invasibility relationships best fit an asymptotic model of invasion reflecting a combination of density-independent and density-dependent processes and that seeds were aggregated within the plant community despite efforts to uniformly sow seeds. Consistent with some models, community invasibility decreased with enhanced soil fertility or reduced levels of disturbance in response to changes in the fraction of safe sites. Our results illustrate that disturbance and soil fertility can be a useful organizing principle for predicting community invasibility, asymptotic models are a reasonable starting point for modeling invasion, and new modeling techniques-coupled with classic experimental approaches-can enhance our understanding of the invasion process.
(29%) compared with control plots, and this increase was highest in grasslands with intermediate productivity. The increased diversity after adding seeds was associated with an average increase of aboveground biomass of 36 g m� 2 (14.8%) compared with control plots. Thus, our results demonstrate that a positive relationship between changes in species richness and productivity, as previously reported from experimental plant communities, also holds for natural grassland ecosystems. Our results show that local plant communities are dispersal limited and a hump-shaped model appears to be the limiting outline of the natural diversity-productivity relationship. Hence, the effects of dispersal on local diversity can substantially affect the functioning of natural ecosystems.
Fretwell and Oksanen's theory of trophic dynamics was tested in two plant communities located in a North Derbyshire dale, including: (1) a low productivity calcareous grassland; and, (2) a highly productive Urtica dioica (nettle) patch. Two methods (herbivore removal through pesticide application, and transplanting established, intact turves (0.5 m(2)) between the two community types) were employed, and analysed in a two-way ANOVA, to test the hypothesis that highly productive communities are controlled by 'top-down' forces and low productivity communities are controlled by 'bottom-up' forces. The Fretwell-Oksanen theory proposes that herbivores limit growth in low productivity communities, not highly productive communities. Therefore, removal of herbivores will result in an increase in plant biomass only in the low productivity community. The results presented in this paper support the Fretwell-Oksanen hypothesis. Furthermore, when small turves were transplanted from the highly productive community to the low productivity community the removal of herbivores through pesticide application greatly increased the above-ground plant biomass. This result suggests, firstly, that the vegetation grown in a highly productive environment is generally very palatable, and secondly, it strengthens the evidence that herbivores are limiting plant growth in low productivity communities but not highly productive communities. Individual plant species response to herbivore removal was related to known relative growth rate values using linear regression and was found to be significant in one case: nettle turves transplanted into the grassland. In this case, relative growth rate accounted for 68.3% of the variation in the response of the plants to herbivore removal. This suggests that fast-growing plants from a highly productive environment are most likely to respond to the release of a limiting factor, in this case herbivory, within a community.
It is shown that invading species are most likely to establish where levels of competition among the resident species are lowest. Thus, of the higher trophic levels, herbivores are more likely to establish than carnivores or detritivores. Invading plants are most likely to establish in communities where the average level of cover is low. Competition is certainly not the only important process involved in establishment, however. Analysis of invasions by insects released as biocontrol agents against weeds, where exploitation and interference are likely to be negligible, show that the probability of successful establishment is closely related to the insect's intrinsic rate of increase. The main biological causes of failure are generalist predators, with parasites and diseases rather less important. For herbivorous insects, host-plant incompatibility is a major cause of failure in establishment. A general model for the dynamics of an invading species is proposed, which stresses: (a), the importance of distinguishing explicitly between exploitation and interference competition; (b), the potential importance of generalist natural enemies; (c), the role of mutualists; (d), the importance of refuges of various kinds in affecting the probability of establishment. Examples are provided to emphasize how far we still are from real, predictive ability in relation to the likely success of proposed or anticipated invasions.
The hypothesis that younger successional stages are less resistant to invasions than older stages was verified experimentally in two kinds of primary successional seres (sand pit and peat-bog disturbed by peat extraction) in southern Bohemia, Czech Republic. Three comparable successional stages aged 0 (i.e. the year of disturbance), 10 and 25 years were selected in both sites. Eight species alien to Czech flora were sown into particular sites and stages and their establishment was recorded. MANOVA revealed significant (P
Declining biodiversity represents one of the most dramatic and irreversible aspects of anthropogenic global change, yet the ecological implications of this change are poorly understood. Recent studies have shown that biodiversity loss of basal species, such as autotrophs or plants, affects fundamental ecosystem processes such as nutrient dynamics and autotrophic production. Ecological theory predicts that changes induced by the loss of biodiversity at the base of an ecosystem should impact the entire system. Here we show that experimental reductions in grassland plant richness increase ecosystem vulnerability to invasions by plant species, enhance the spread of plant fungal diseases, and alter the richness and structure of insect communities. These results suggest that the loss of basal species may have profound effects on the integrity and functioning of ecosystems.
An experiment was conducted to lest the hypothesis that interspecific variation in rates of leaf litter decomposition arises as a consequence of differences in the anti-herbivore defences of the living leaf. Leaf palatability was assayed in 54 vascular plant species of widespread occurrence in the British Isles, using the generalist herbivore Helix aspersa (garden snail) and the omnivore Acheta domestica (a cricket). The results were then compared with published standardised measurements of litter decomposition rate available for 43 of the species. There was convincing support for the hypothesis, in the form of a significant positive correlation between leaf palatability and lifter decomposition rate. The correlation was also evident within subsets consisting of monocots or dicots. The results suggest a critical role for anti-herbivore defences in the link between aboveground and belowground processes in ecosystems.
In an experimental test of plant community invasibility, we introduced seeds of a native ruderal, California poppy (Eschscholzia californica), at fixed density into experimental plots in a California winter annual grassland. Each of the 42 plots, which ranged in size from 2 m(2) to 32 m(2), had been studied for 4 yr previous to the introduction, with the common observation that a subset of plots of each size consistently held more species than others. It was primarily in these more species-rich plots that establishment and reproduction by the experimental invader occurred. Success of the invader per plot. measured as the total number of plants germinating, producing seeds, or perennating, varied with plot size, but the statistical contribution of plot size was secondary to that of local species number. Contributing variables were the extent of small mammal disturbance (positive) and the degree to which a single resident plant species (in particular, Bromus diandrus) dominated a plot (negative). In contrast to theories of competitive exclusion via niche partitioning, species-rich plots were more invasible.
The characteristics of invading species were explored using the Ecological Flora Database, and by using comparisons available in other studies. Invasion success has been related to both abundance and distribution in the native range, which are themselves related. Abundance is probably the key variable. In the British flora invading species are characterized more by their distribution and morphology than by their life history and reproductive behaviour. The size of the plant and characters related to propagule pressure created by humans come out as important correlates of success. For biological characters, genetic studies and the phenomenon of boom-and-bust both suggest that the critical interaction between species and habitat is often subtle. Nevertheless, studies on pines and squirrels show that such important biological characters can be determined.
Why do different plant species thrive where they do? This is a difficult
question to answer because plants have invaded new niches and
subsequently evolved to become better adapted within those niches.
Distinguishing the traits that allow successful invasion and those that
are evolved adaptations to current environments is not usually possible.
We attempt to identify life history components that allow successful
invasion by analysing the life history variables and ecological
requirements of plant species that have successfully invaded the U.K. in
recent years. The British flora is uniquely suited for this analysis
because we have precise information on the dates of arrival, rates of
spread and final spatial distribution of all our alien vascular plant
species. Data on alien plants controls for evolution after invasion
because there has been relatively little time for evolution to occur. We
use modern phylogenetically-based comparative methods in an attempt to
tease apart those components of life histories that have allowed
successful invasion (large seeds, tall stature, protracted seed
dormancy) from those that are irrelevant (dispersal syndrome, mating
system, leaf shape).
1 The invasion of habitats by non-native plant and animal species is a global phenomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdotal and resistant to generalization.
2 Here, we use insights from experiments and from long-term monitoring studies of vegetation to propose a new theory in which fluctuation in resource availability is identified as the key factor controlling invasibility, the susceptibility of an environment to invasion by non-resident species. The theory is mechanistic and quantitative in nature leading to a variety of testable predictions.
3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a variety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules.
Some theories and experimental studies suggest that areas of low plant spe- cies 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 in- vasions in rare habitats and distinctive plant communities pose a significant challenge to land managers and conservation biologists.
This identification guide to the vascular flora of Britain and Ireland is drawn up from actual plant material and covers all natives, naturalized plants, crop plants and recurrent casuals: 2990 species and 197 extra subspecies are treated fully, with 559 hybrids and marginal species mentioned more briefly. The information, for each family or similar taxon, is presented in the form of an introductory summary of characteristics generally followed by a dichotomous key to genera; for each genus or similar taxon, a brief summary is followed by a dichotomous key to species and then by individual descriptions of the keyed species. These descriptions include other species not mentioned in the keys, as well as hybrids and subspecies. They also give information on status, habitat, distribution and frequency of occurrence or rarity, and indicate endemic or extinct plants. Within the book are interspersed 150 pages of illustrations and photographs of difficult groups. There is a glossary of terms used and an index combining common and Linnean names. -J.W.Cooper
The mechanisms of successional change were analysed in a mediterranean coastal grassland undergoing post-grazing succession at Sea Ranch, northern California, U.S.A. The study included field experiments and observations on the five most abundant species, including four perennial grasses and one annual grass. The results explain the observed trends in the populations, and allow prediction of future change. Patchiness in species distributions, dispersal ability, and localised disturbances strongly affected the outcomes of species interactions. Competitive ability was found to have two distinct components, inhibition and invasion, which were not well correlated. Overall, the analyses show that it is possible to link population and community ecology effectively using appropriate field methods, at least in simple communities.
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.
Attempts to predict which species will become invaders and those which will not, represent one of the main areas of interest in the study of biological invasions. At present, however, only very limited generalizations are available, based on plant physiology, genetics, demography, species behaviour in other countries, or behaviour of congeneric species. Here I report that invasiveness of pines (genus Pinus) and, very likely, other woody species of seed plants in disturbed landscapes, is predictable on the basis of a small number of attributes: small mean seed mass, short juvenile period, and short mean interval between large seed crops. Moreover, vertebrate dispersal is responsible for success of many woody invaders in disturbed as well as 'undisturbed' habitats. As for herbaceous species, their primary (native) latitudinal range seems to be the best predictor of invasiveness, at least for species introduced from Eurasia to North America.
Estimations have been made of the maximum potential relative growth-rate (Rmax) attained in the exponential phase by 132 species of flowering plants including representatives from each of the dry terrestrial habitats of the Sheffield region. The period of growth between two and five weeks after germination was studied in a standardized, productive environment and fitted growth-curves were used to derive various growth-analysis parameters. Woody species exhibited a bias towards low values of Rmax and a similar trend was evident among fine-leaved grasses. Annual plants were most frequent in the high Rmax category. Grasses and forbs included a wide range of growth-rates and in both, high values of Rmax were associated with a variety of growth forms. With the exception of the woody plants and the biennial herbs, Anthriscus sylvestris and Heracleum sphondylium, all the species of low Rmax examined were species which as seedlings and mature plants tend to be small in stature. The possibility that Rmax is of adaptive significance in the field was tested by examining the frequency of species of low or high Rmax in vegetation samples from a range of habitat types. In several disturbed and/or productive habitats fast-growing species were predominant and species of low Rmax were virtually or completely absent. The reverse was true of several stable, unproductive habitats. Species of moderate Rmax were ubiquitous. The adaptive significance of Rmax and its contribution to the determination of herbaceous vegetation are explored by recognizing three primary strategies in herbaceous plants. In the `competitive' strategy, high Rmax coincides with tall stature, extensive lateral spread and the tendency to accumulate leaf litter, all characteristics which facilitate the exclusive occupation of productive, undisturbed habitats. The `ruderal' strategy also involves high Rmax but here it is associated with a short life-history in which much photosynthate is directed into seeds. The potential for rapid growth allows such plants an opportunist exploitation of disturbed habitats. The third strategy, that of the `stress-tolerant' plant, is characterized by a low potential relative growth-rate and small stature. Maximum potential relative growth-rate thus appears to be of general significance in the determination of vegetation composition, but in individual habitats this composition is also considered to be dependent upon additional plant characteristics.
A long-term research programme, conducted mainly in northern England, has involved field surveys (1965-77), laboratory screening (1974-96), monitoring of permanent plots (1958 to date) and manipulative experiments (1987 to date). The so-called C-S-R classification of plant functional types developed from all this activity. Patterns of covariation among the traits used in the classification have recently been validated in this journal. The C-S-R classification appears to be applicable to vegetation in general. It thus has considerable potential for interpreting and predicting vegetation and ecosystem properties on a world-wide scale. However, to realize this potential we need to develop simplified procedures to extrapolate the C-S-R system to the many species which have not been the subject of previous ecological investigation. Here we describe a rapid method for attribution of C-S-R type and we test its accuracy in Britain by comparing it with an independent classification based upon more laborious procedures. The new method allocates a functional type to an unknown herbaceous subject using few, simple predictor variables. We have developed spreadsheets to perform all of the necessary calculations. These may be downloaded from the UCPE website at http://www.shef.ac.uk/uni/academic/N-Q/nuocpe, or obtained by direct application to the E-mail address ucpe@sheffield.ac.uk
A long-term field experiment in limestone grassland near Buxton (North Derbyshire, United Kingdom) was designed to identify plant attributes and vegetation characteristics conducive to successful invasion. Plots containing crossed, continuous gradients of fertilizer addition and disturbance intensity were subjected to a single-seed inoculum comprising a wide range of plant functional types and 54 species not originally present at the site. Several disturbance treatments were applied; these included the creation of gaps of contrasting size and the mowing of the vegetation to different heights and at different times of the year. This paper analyzes the factors controlling the initial phase of the resulting invasions within the plots subject to gap creation. The susceptibility of the indigenous community to invasion was strongly related to the availability of bare ground created, but greatest success occurred where disturbance coincided with eutrophication. Disturbance damage to the indigenous dominants (particularly Festuca ovina) was an important determinant of seedling establishment by the sown invaders. Large seed size was identified as an important characteristic allowing certain species to establish relatively evenly across the productivity-disturbance matrix; smaller-seeded species were more dependent on disturbance for establishment. Successful and unsuccessful invaders were also distinguished to some extent by differences in germination requirements and present geographical distribution.
Two of the central hypotheses of the triangular model of primary plant strategies were tested by a movel technique involving seven grasses of contrasted ecology grown in pure stands and an additive mixture on an experimental matrix of crossed gradients of mineral nutrient stress and vegetation disturbance. The experimental design allowed reductions in vegetative and reproductive vigor resulting from interspecific competition to be distinguished from those arising from direct effects of nutrient stress and vegetation disturbance. It was also possible to determine the extent to which competitive suppression of each species was affected by stress and disturbance. In isolation, all species showed maximum vegetative and reproductive vigor at high soil fertility and low disturbance. In the mixture, absolute reductions in biomass and flowering due to competition were greatest at high soil fertility and low disturbance, and the species of most extreme strategy became restricted to areas of the matrix broadly consistent with those predicted by strategy classification. When standardized for differences in biomass in pure stands, the effect of competition remained relatively constant across the stress-disturbance matrix for all species except Poa annua, which was less restricted by competition at high intensities of stress. There were marked and consistent differences between species in their susceptibility to competition. At both high and low soil fertility, two species of natural occurrence on infertile soils (Festuca ovina, Bromus erectus) were poor competitors relative to Arrhenatherum elatius, a widespread dominant of productive grasslands. The effect of competition was least severe on flowering of annuals in low-stress portions of the matrix. If competition is assessed simply as the percentage of reduction in biomass between pure and mixed stands it appears that competition intensity is constant across different intensities of stress and disturbances. However, observations that maximum reductions in biomass coincided with low stress and low disturbance, that competition decreased in importance as a factor reducing yield and flowering (relative to stress and disturbance) as stress and disturbance intensities increased, and that there was a consistently inferior competitive ability of plants from infertile soils at all positions on the matrix all support the hypothesis that competition declines in importance as a vegetation determinant in the vegetation of infertile soils.
(1) Using a standardized procedure, a laboratory study was made of the germination characteristics of seeds collected from a wide range of habitats in the Sheffield region. Measurements were conducted on freshly-collected seeds and on samples subjected to dry storage, chilling and scarification. Responses to temperature and light flux were also examined. (2) The data have been used to compare the germination biology of groups of species classified with respect to various criteria including life-form, family, geographical distribution, ecology, and seed shape, weight and colour. (3) Marked differences were observed in the capacity of freshly-collected seeds for immediate germination. Of the 403 species examined, 158 failed to exceed 10% germination but 128 attained values greater than 80%. Germination was high in the majority of grasses and low in many annual forbs and woody species. With respect to initial germinability, major families could be arranged in the series Gramineae > Compositae > Leguminosae = Cyperaceae > Umbelliferae. Many small-seeded species were able to germinate immediately after collection and seeds of these species were often elongated or conical and had antrorse hairs or teeth on the dispersule. High initial germinability was conspicuous among the species of greatest abundance in the Sheffield flora. (4) In the majority of species, germination percentage increased during dry storage; this effect was most marked in small-seeded species. Among the seventy-five species which responded to chilling, some germinated at low temperature in darkness whilst others were dependent upon subsequent exposure to light or to higher temperature or to both. Responses to chilling were characteristic of the Umbelliferae. In all of the legumes examined, rapid germination to a high percentage was brought about by scarification. (5) Under the experimental conditions, all of the annual grasses showed the potential for rapid germination. High rates were also observed in many of the annual forbs and perennial grasses. Low rates of germination occurred in the majority of sedges, shrubs and trees, and were particularly common in species of northern distribution in Britain. Rapid germination was characteristic of the species of greatest abundance in the Sheffield flora. Rate of germination showed a progressive decline with increasing seed weight, and, with some exceptions, there was a positive correlation between rate of germination and the relative growth rate of the seedling. (6) In sixteen species, germination in the light was found to be dependent upon exposure to diurnal fluctuations in temperature. Under constant temperature conditions, the majority of grasses, legumes and composites germinated over a wide range of temperature, and the same feature was evident in species of ubiquitous or southern distribution in the British Isles. A requirement for relatively high temperature was apparent in sedges, in plants of northern distribution and in a majority of the marsh plants. The range of constant temperatures conducive to germination tended to be wider in grassland plants than in woodland species. Rapid germination over a wide range of temperature occurred in many of the species which attain greatest abundance in the Sheffield flora. (7) Although germination in most species was promoted by light, some were inhibited under relatively high light flux. In 104 species a marked reduction in germination occurred if seeds were kept in the dark, and in many species this inhibitory effect could be intensified by either or both excluding temperature fluctuations and abandoning the use of a green `safety' light. The capacity for germination in darkness was observed in all of the legumes and many of the grasses. Dark germination did not occur in the Cyperaceae and was uncommon in the Compositae. The inhibitory effect of darkness was characteristic of many of the species known to form reserves of buried seeds, but it occurred also in certain species with more transient seed banks. (8) There were recurrent associations between features of seed morphology and of germination, several of which coincided with particular ecological characteristics. (9) The functional significance of some of the germination characteristics observed in this study leads us to the conclusion that certain regenerative mechanisms in the field may be predicted from the laboratory characteristics of the seed.
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.
The question as to why some communities are more invasible than others has pro-found implications for conservation biology and land management. The theoretical issues involved go right to the heart of our understanding of species coexistence and community assembly. The experiment reported here indicates that for productive, small-scale grassland plots, species identity matters more than species richness in determining both the number of invading species and the total biomass of invasives.
The Royal Society for the Protection of Birds (RSPB) is attempting to restore heathland and acid grassland on 158 ha of ex-arable land at their Minsmere reserve; the aims being to join existing small heathland fragments together and provide habitat for the conservation of three rare birds — the stone curlew (Burhinus oedicnemus) the woodlark (Lullula arborea) and the nightjar (Caprimulgus europaeus). The ex-arable soils have been shown to have a higher pH (pH >6) than the adjacent heaths (pH 3.5–4), and it has been suggested that soil acidification will be needed to ensure successful heathland establishment. This paper reports the results of an experiment where elemental S (0–12 t S ha−1) has been added to acidify these ex-arable soils in factorial combination with Calluna seed added in cut shoots. The effects of these treatments on the establishment of (a) Calluna, (b) ruderal species and (c) plant communities were assessed. The main result is that the cover of the ruderal species was significantly reduced where the soils had been acidified, which should help Calluna to establish. However, Calluna establishment was relatively poor, mainly because of inadequate weed control in the early phases, but seedlings were most abundant where S was applied at between 1 and 4 t S ha−1. We tentatively suggest that the most appropriate treatment is to apply 4 t S ha−1, a rate that gives acidification to the appropriate range and maintains good control of ruderal species. Weed control is essential at the time of adding the Calluna seed.
Each one of the 24 nature reserves in the preceding case studies has received introduced species of plants and vertebrates (and invertebrates where the data exist). Some of these have become invasive, although the probability that an island nature reserve is invaded is greater than a savanna or dry woodland. Arid lands and Mediterranean-type reserves showed a negative relationship between the proportion of species that are introduced and the reserve's area. Examples demonstrate that after a period of about 1000 years it is difficult to distinguish between native and introduced species.Invasive species affect both the structure and function of an ecosystem. Management priority has to be given both to invasive species that threaten endemic species with extinction and to species that have a strong landscape effect. The cost of controlling invasive species can utilise a large proportion of a reserve manager's recurrent budget. Tourism poses dangers for reserves since there is a positive correlation between visitation rate and the number of introduced species.The most important generalisation is that all nature reserves, except those in Antarctica, appear to have invasive species. Managers face the problem of how best to conserve ecological variety.
Much as Rachel Carson's "Silent Spring" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic "The Ecology of Invasions by Animals and Plants" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. "History has caught up with Charles Elton's foresight, and "The Ecology of Invasions" can now be seen as one of the central scientific books of our century."-David Quammen, from the Foreword to "Killer Algae: The True Tale of a Biological Invasion"
We compare the ecological and habitat characteristics of alien and native vascular plants which have recently expanded in range m England, Scotland, the Republic of Ireland and the Netherlands In the great majority of respects, expanding aliens and natives are functionally indistinguishable However, there are a few consistent differences aliens are more likely than natives to be clonal, polycarpic perennials with erect, leafy stems, and to have transient seed banks We discuss these trends m the context of the difficulties faced by aliens in invading mostly closed plant communities in relatively cool, damp climates Our results are consistent with some predictions of the attributes of‘ideal’invaders, but contradict others We argue that the ecological attributes of successful alien invaders are strongly habitat-dependent
Invasibility of riparian plant communities was estimated by the percentage of alien species found along the Adour River (Southwest France) and along Lockout Creek, McKenzie River, and Willamette River (Central Cascades, Oregon, U.S.A.). At the patch scale, the invasibilities of riparian plant communities were compared between one exceptionally rich site of the Adour River and patches selected in the Hoh and Dungeness watersheds (Olympic Peninsula, Washington, U.S.A.). Alien species represented 24% of 1396 species for the Adour and 30% of 851 species for the McKenzie. They represented 24% of 148 species for the Hoh drainage and 28% of 200 species for the Dungeness drainage. Similar trends were found along the Adour River and along the McKenzie River for changes in total number of species per site and in percentages of alien species per site. These trends may be related to the intermediate disturbance regimes and to the physical structure of the riparian corridors. Climatic and human factors are also involved in these longitudinal changes. Positive linear relationships were found between the total number of species and the percentage of aliens observed in each site. At the patch scale, most of the sampled communities contained alien species. Although mature vegetative patches appeared to be invasible, young communities contained more alien species than older ones. For entire corridors, a positive linear relationship was found between total species richness and percentage of alien species in each patch type for the richest site of the Adour River. This may be partially explained by landscape features considered in a successional context. We suggest the use of empirical rules, and stress the importance of riparian systems for monitoring the conservation of local and regional species pools are suggested.
Mineral nutrient concentrations were determined in leaves of 83 mostly herbaceous species collected from central England. Most samples were analysed for N, P, K, Ca, Mg, Na, Fe, Al, Mn, Cu and Zn. Concentrations of K, N and P showed similar levels of interspecific variability, with the highest concentrations being 6–9 times the lowest. Mg and (especially) Ca were much more variable, with the highest concentrations being 24 and 49 times the lowest respectively. Only in the case of P concentration was the majority of the variance in the data found at or below the species level. Most of the variance in Ca and Mg concentrations was between monocots and dicots. Concentrations of N and P were strongly positively correlated with each other. Only Ca and Mn were consistently associated with soil pH, positively and negatively respectively. Dicots tended to accumulate more Ca and Mn from high soil concentrations than did monocots. Concentration of P was significantly positively correlated with maximum potential relative growth rate. Plants of woodland and arable habitats contained high concentrations of P, and those of pasture and skeletal habitats contained low concentrations of P. The P: N ratio was higher in plants of arable habitats. Species with P-rich leaves tended to be currently increasing in abundance. The results suggest that plants with nutrient-rich foliage grow quickly, dominate nutrient-rich ecosystems and are generally increasing as a result of the eutrophication and disturbance arising from human exploitation.
How Important are Rivers for Supporting Plant Invasions? The Giant Hogweed Problem in Sweden: Suggestions for its Management and Control Giant Hogweed and its Control in Scotland Controlling Invasive Weeds using Glyphosate Alien Weeds - A National Rivers Authority Perspective.
This book summarizes knowledge about invasive species and the problems that they cause in 7 chapters, with the following titles: a framework for the study of invasions; the origins and success and failure of invasions; which communities are invaded by which type of species; the process of spread; ecological consequences of invasions; genetic and evolutionary effects; and implications and communities. Author and subject indexes are provided.
With a simple model, I show that comparisons of invasibility between regions are impossible to make unless one can control for all of the variables besides invasibility that influence exotic richness, including the rates of immigration of species and the characteristics of the invading species themselves. Using data from the literature for 184 sites around the world, I found that nature reserves had one-half of the exotic fraction of sites outside reserves, and island sites had nearly three times the exotic fraction of mainland sites. However, the exotic fraction and the number of exotics were also dependent on site area, and this had to be taken into account to make valid comparisons between sites. The number of native species was used as a surrogate for site area and habitat diversity. Nearly 70% of the variation in the number of exotic species was accounted for by a multiple regression containing the following predictors: the number of native species, whether the site was an island or on the mainland, and whether or not it was a nature reserve. After controlling for scale, there were significant differences among biomes, but not continents, in their level of invasion. Multiple biome regions and temperate agricultural or urban sites were among the most invaded biomes, and deserts and savannas were among the least. However, there was considerable within-group variation in the mean degree of invasion. Scale-controlled analysis also showed that the New World is significantly more invaded than the Old World, but only when site native richness (probably a surrogate for habitat diversity) is factored out. Contrary to expectation, communities richer in native species had more, not fewer, exotics. For mainland sites, the degree of invasion increased with latitude, but there was no such relationship for islands. Although islands are more invaded than mainland sites, this is apparently not because of low native species richness, as the islands in this data set were no less rich in native species than were mainland sites of similar area. The number of exotic species in nature reserves increases with the number of visitors. However, it is difficult to draw conclusions about relative invasibility, invasion potential, or the roles of dispersal and disturbance from any of these results. Most of the observed patterns here and in the literature could potentially be explained by differences between regions in species properties, ecosystem properties, or propagule pressure.
1 Using data from a survey of over 10 000 1-m2 quadrats in a 3000-km2 area, we examined the relationship between abundance and range for the vascular plant flora of central England.
2 At the level of the whole landscape, abundance was not related to local, regional or national range. Local, regional and national range were closely related to each other.
3 At the level of the whole landscape, range was significantly and positively related to both niche breadth (expressed as the range of habitats exploited) and to habitat availability, although niche breadth appeared to be more important. Abundance was not related to niche breadth or habitat availability. Since specialist species are mainly confined to uncommon habitats (especially wetlands), we conclude that the relationship between range and niche breadth is not an artefact of widespread species passively sampling more habitats.
4 At the level of individual habitat types, significant positive relationships between range and abundance were common. These relationships remained after controlling for the effects of phylogeny. For predominantly annual weed communities, the relationship was linear, but for perennial communities it was markedly ‘upper triangular’, i.e. all combinations of range and abundance were found except wide range/low abundance. The evidence suggests that this difference can be attributed to the greater mobility of annual weeds.
Successful colonization of B. pinnatum at Buxton, at the northern edge of its range in Britain, suggests that lack of dispersal is currently preventing its northward extension. On first inspection, the causes of distributional limits of B. pinnatum appear to be similar to those restricting the northward extensions of populations of Cirsium acaule; the two species occur in similar habitats and their geographical distributions coincide. Work by Pigott (1968) demonstrated that C. acaule was restricted at its northern outposts by limitations on seed production and dispersal. When these barriers are overcome, however, C. acaule appears to be fully capable of local persistence and consolidation by rhizome expansion. This conclusion is supported by the observation that isolated populations of some antiquity of both species are known to occur in north Derbyshire (Clapham 1969). There is no doubt that extensive rhizome expansion has been responsible for the spread of B. pinnatum at Buxton. However, the potential for further spread of B. pinnatum by seed dispersal cannot be discounted. Seed production by B. pinnatum at Buxton was examined in 1999 and 2000 and it was found to be producing large numbers of viable seed. Consequently, further research is required to examine whether the failure of existing north Derbyshire populations of B. pinnatum to spread is due to climate or self-incompatibility. Work by Schlapfer & Fischer (1998) on natural populations of B. pinnatum suggest a very low ratio of sexual vs. vegetative recruitment, notwithstanding their detection of high clonal diversity.
Plant species composition, species abundances, and species richness were strongly recruitment limited in a 4-yr experiment in which seeds of up to 54 species were added to patches of native grassland. Four field seasons after a one-time addition of seed, many added species were still present and reproducing, with plots seeded at the highest rate having species richness that was 83% greater and total plant cover that was 31% greater than controls. Total plant community cover increased significantly with the number of species added as seed, but total cover of pre-existing species was independent of the number of species added as seed, suggesting that the new species mainly filled previously ''empty'' sites. The proportion of added species that became established was negatively correlated with initial species richness of plots, suggesting that species-rich sites were more resistant to invasion. Plot invasibility also depended on the abundances and species richness of plant functional groups in the plots, but was independent of seed size and of total plant cover. The major functional groups of plants differed in their abilities to invade as seed, with perennial grasses being the poorest invaders and herbaceous legumes being the best. Thus, local biotic interactions and recruitment dynamics jointly determined diversity, species composition, and species abundances in these native grassland communities. This supports a metapopulation-like perspective over a purely interspecific-interaction perspective or a purely regional perspective, suggesting that recruitment limitation may be more important, even on a local scale, than often recognized.
It is commonly believed that diverse communities better resist invasion by exotic species than do simple communities. We examined the history of this notion, and evaluated theoretical and empirical work linking diversity and invasions. We found that much of the historical work that has contributed to the perception that diverse communities are less invasible, including Elton's observations and MacArthur's species-packing and diversity-stability models, is based on controversial premises. Nevertheless, more recent theoretical studies consistently supported the predicted negative relationship between diversity and invasibility. The results of empirical studies, however, were decidedly mixed. Constructed community studies directly manipulating diversity found both positive and negative effects of diversity on invasibility in both field and microcosm settings. Other empirical studies tracking the assembly of ecological communities generally suggested that communities decline in invasibility as species accumulate over time, though the role of diversity itself was often ambiguous. Studies of the spatial correlation between diversity and invasion and studies experimentally adding invaders to natural systems indicated that diverse communities tend to be more invasible. We argue that these results most likely reflect environmental factors spatially covarying with diversity in natural communities (e.g. resources, disturbance), and not the effects of diversity itself as uncovered by constructed community studies. Nevertheless, the consistent positive relationship between exotic species abundance and resident species diversity found in spatial pattern studies suggests that invaders and resident species are more similar than often believed, and the implications of this for theories of invasion are discussed.