Can fungal endophytes fast-track plant adaptations to climate change?

Rapid climate change threatens plant communities. While many studies address the impact of climate change on plants and mechanisms of their resilience to climate stressors, the role of the plant microbiome in aiding plants' adaptation to climate change has been less investigated. We argue here that fungal endophytes, an important constituent of the plant microbiome, may be key to the ability of plants to adapt to climatic stressors. The rapid adaptive response of endophytes coupled with their ability to ‘transfer’ resistance to their hosts may fast-track plants' adaptation to climate change. We briefly review the importance of Class 3 fungal endophytes of terrestrial plants and discuss how they may accelerate adaptations to climate change in crops and natural plant communities and call for efforts directed at improving the understanding of fungal endophyte-facilitated plant health. Such information could aid in devising improved strategies for mitigating climate change effects on plant communities.     

Comparing the recovery of richness,structure, and biomass in naturally regrowing and planted reforestation

The clearing of natural vegetation for agriculture has reduced the capacity of natural systems to provide ecosystem functions. Ecological restoration can restore desirable ecosystem functions, such as creating habitat for animal conservation and carbon sequestration as woody biomass. In order to maintain these beneficial ecosystem functions, restoration projects need to mature into self‐perpetuating communities. Here we compared the ecological attributes of two types of restoration, “active” tree plantings with “passive” natural forest regeneration (“natural regrowth”) to existing remnant vegetation in a cleared agricultural landscape. Specifically, we measured differences between forest categories in factors that may predict future restoration failure or ecosystem collapse: aboveground plant biomass and biomass accrual over time (for regrowing stands), plant density and size class distributions, and diversity of functional groups based on seed dispersal and growth strategy traits. We found that natural regrowth and planted forests were similar in many ecological characteristics, including biomass accrual. Despite this, planted stands contained fewer tree recruit and shrub individuals, which may be due to limited recruitment in plantings. If this continues, these forests may be at risk of collapsing into nonforest states after mature trees senesce. Lower shrub density and richness of mid‐story trees may lead to lower structural complexity in planting plots, and alongside lower richness of fleshy‐fruited plant species may reduce animal resources and animal use of the restored stand. In our study region, natural regrowth may result in restored woodland communities with greater conservation and carbon mitigation value.     

Environmental changes affect the assembly of soil bacterial community primarily by mediating stochastic processes

Both ‘species fitness difference’‐based deterministic processes, such as competitive exclusion and environmental filtering, and ‘species fitness difference’‐independent stochastic processes, such as birth/death and dispersal/colonization, can influence the assembly of soil microbial communities. However, how both types of processes are mediated by anthropogenic environmental changes has rarely been explored. Here we report a novel and general pattern that almost all anthropogenic environmental changes that took place in a grassland ecosystem affected soil bacterial community assembly primarily through promoting or restraining stochastic processes. We performed four experiments mimicking 16 types of environmental changes and separated the compositional variation of soil bacterial communities caused by each environmental change into deterministic and stochastic components, with a recently developed method. Briefly, because the difference between control and treatment communities is primarily caused by deterministic processes, the deterministic change was quantified as (mean compositional variation between treatment and control) – (mean compositional variation within control). The difference among replicate treatment communities is primarily caused by stochastic processes, so the stochastic change was estimated as (mean compositional variation within treatment) – (mean compositional variation within control). The absolute of the stochastic change was greater than that of the deterministic change across almost all environmental changes, which was robust for both taxonomic and functional‐based criterion. Although the deterministic change may become more important as environmental changes last longer, our findings showed that changes usually occurred through mediating stochastic processes over 5 years, challenging the traditional determinism‐dominated view.     

Relative contributions of neutral and niche-based processes to the structure of a desert grassland grasshopper community

Whether neutral or deterministic factors structure biotic communities remains an open question in community ecology. We studied the spatial structure of a desert grassland grasshopper community and tested predictions for species sorting based on niche differentiation (deterministic) and dispersal limitation (neutral). We contrasted the change in species relative abundance and community similarity along an elevation gradient (i.e., environmental gradient) against community change across a relatively homogeneous distance gradient. We found a significant decrease in pairwise community similarity along both elevation and distance gradients, indicating that dispersal limitation plays a role in structuring local grasshopper communities. However, the distance decay of similarity was significantly stronger across the elevational gradient, indicating that niche-based processes are important as well. To further investigate mechanisms underlying niche differentiation, we experimentally quantified the dietary preferences of two common species, Psoloessa texana and Psoloessa delicatula, for the grasses Bouteloua eriopoda and Bouteloua gracilis, which are the dominant plants (~75% of total cover) in our study area. Cover of the preferred host plant explained some of the variation in relative abundances of the two focal species, although much variance in local Psoloessa distribution remained unexplained. Our results, the first to examine these hypotheses in arid ecosystems, indicate that the composition of local communities can be influenced by both probabilistic processes and mechanisms based in the natural histories of organisms.     

Dispersal and seed limitation affect diversity and productivity of montane grasslands

So far, seed limitation as a local process, and dispersal limitation as a regional process have been largely neglected in biodiversity–ecosystem functioning research. However, these processes can influence both local plant species diversity and ecosystem processes, such as biomass production. We added seeds of 60 species from the regional species pool to grassland communities at 20 montane grassland sites in Germany. In these sites, plant species diversity ranged from 10 to 34 species m⁻² and, before manipulation, diversity was not related to aboveground biomass, which ranged from 108 to 687 g m⁻². One year after seed addition, local plant species richness had increased on average by six species m⁻² (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.     

Size matters in regulating the biodiversity of tropical forest soils

Tropical forests have long fascinated ecologists, inspiring a plethora of research into the mechanisms regulating their immense biodiversity, which originally captured the interests of early natural historians and explorers, and that still persists to this day. A new focus of this research emerged in the early 2000s highlighting the potential role of neutral (stochastic) processes in regulating the composition and diversity of tropical forest communities, and thus the maintenance of a large portion of global biodiversity (Hubbell, 2001). This strictly contrasted the long‐held belief that communities assembled via the sorting of species (and their abundances) via a deterministic response to local abiotic and biotic environmental conditions, reflecting the niche of each species (Leibold & McPeek, 2006). Yet, it is unlikely that the assembly of any community is solely governed by either stochastic or deterministic processes, but instead a combination of both. However, whether deterministic processes via niche‐based environmental sorting of species, or stochastic processes reflecting pattens of dispersal limitation, neutral effects and ecological drift dominate is often unclear. This prompts questions as to whether the relative influence of one process over another is dependent on the scale (spatial or temporal) or context of the study, or specific traits of the taxa under investigation (e.g., body size). In a From the Cover paper in this issue of Molecular Ecology, Zinger et al. (2018) tackle all these issues and show, among other things, that for soil microbes and mesofauna from tropical forests, the relative contribution of stochastic and deterministic processes in assembling their communities is strongly dependent on the body size or the studied taxa.     

Contrasting trait assembly patterns in plant and bird communities along environmental and human‐induced land‐use gradients

Human‐driven environmental changes can induce marked shifts in the functional structure of biological communities with possible repercussion on important ecosystem functions and services. At the same time it remains unclear to which extent these changes may differently affect various types of organisms. We investigated species richness and community functional structure of species assemblages at the landscape scale (1 km² plots) for two contrasting model taxa, i.e. plants (producers and sessile organisms) and birds (consumers and mobile organisms), along topography, climate, landscape heterogeneity, and land‐use (agriculture and urbanization) gradients in a densely populated region of Switzerland. Our study revealed that agricultural and urban land uses drove marked shifts in the functional structure of biological communities compared to changes along climate and topography gradients, especially for plants, while for birds these changes were comparable. Agricultural and urban land uses enhanced divergence in traits related to resource use for birds (diet and nesting), growth forms, dispersal, and reproductive traits for plants, while it induced convergence in vegetative plant traits (plant height and leaf dry matter content). These results suggest that contrasting assembly patterns may arise within and across taxonomic groups along the same environmental gradients as result of distinct underlying processes and ‘organism‐specific’ environmental perceptions. Our results further suggest a potential homogenization of biological communities, as well as low functional diversity and redundancy levels of bird assemblages in our human‐dominated study region. This might potentially compromise the maintenance of key ecological processes under future environmental changes.     

Ecosystem consequences of herbicides: the role of microbiome

Non-target organisms are globally exposed to herbicides. While many herbicides – for example, glyphosate – were initially considered safe, increasing evidence demonstrates that they have profound effects on ecosystem functions via altered microbial communities. We provide a comprehensive framework on how herbicide residues may modulate ecosystem-level outcomes via alteration of microbiomes. The changes in soil microbiome are likely to influence key nutrient cycling and plant–soil processes. Herbicide-altered microbiome affects plant and animal performance and can influence trophic interactions such as herbivory and pollination. These changes are expected to lead to ecosystem and even evolutionary consequences for both microbes and hosts. Tackling the threats caused by agrochemicals to ecosystem functions and services requires tools and solutions based on a comprehensive understanding of microbe-mediated risks.     

Ecosystem functions in natural and anthropogenic ecosystems across the East African coastal forest landscape

Habitat identity and landscape configuration significantly shape species communities and affect ecosystem functions. The conservation of natural ecosystems is of particular relevance in regions where landscapes have already been largely transformed into farmland and where habitats suffer under resource exploitation. The spillover of ecosystem functions from natural ecosystems into farmland may positively influence agricultural productivity and human livelihood quality. We measured three proxies of ecosystem functioning: Pollinator diversity (using pan traps), seed dispersal (with a seed removal experiment), and predation (using dummy caterpillars). We assessed these ecosystem functions in three forest types of the East African dry coastal forest (Brachystegia forest, Cynometra forest, and mixed forest), as well as in adjoining farmland and in plantations of exotic trees (Eucalyptus mainly). We measured ecosystem functions at 20 plots for each habitat type, and along gradients ranging from the forest into farmland. We also recorded various environmental parameters for each study plot. We did not find significant differences of ecosystem functions when combining all proxies assessed, neither among the three natural forest types, nor between natural forest and plantations. However, we found trends for single ecosystem functions. We identified highest pollinator diversity along the forest margin and in farmlands. Vegetation cover and blossom density affected the level of predation positively. Based on our findings, we suggest that flowering gardens around housings and woodlots across farmland areas support ecosystem functioning and thus improve human livelihood quality. We conclude that levels of overall ecosystem functions are affected by entire landscapes, and high landscape heterogeneity, as found in our case, might blur potential negative effects and trends arising from habitat destruction and degradation.     

More Ecology is Needed to Restore Mediterranean Ecosystems: A Reply to Valladares and Gianoli

Valladares and Gianoli (2007) tried to answer a key question, “how much ecology do we need to know to restore Mediterranean ecosystems?” by focusing on (1) plant–plant interactions; (2) environmental heterogeneity and the potential adaptation of transplanted plants; and (3) phenotypic plasticity of the planted species. We consider their choice of topics incomplete and potentially misleading because (1) it is clearly biased toward a narrow set of research topics (phenotypic plasticity, facilitation, and climate change); (2) it assumes that active restoration, and specifically revegetation, is needed; and (3) it conveys a false perception that other basic ecological aspects of Mediterranean ecosystems are sufficiently known. Instead, we review the current knowledge on seed dispersal, succession, and ecosystem functioning for Mediterranean ecosystems. We argue that decades of research on these topics have yielded few practical guidelines for restoration, something that needs to be urgently corrected. First, the current “establishment limitation paradigm” for plant recruitment does not acknowledge the role of dispersal limitation at large spatial scales. More attention should be paid to nucleation processes and directed seed dispersal mediated by animals. Second, studies of vegetation dynamics and succession in the Mediterranean have led to an overly simplistic view of successional dynamics. How fast and deterministic succession is remains mostly unexplored; long‐term monitoring of successional dynamics at different spatial scales is urgently needed. Third, information on the functional status of Mediterranean ecosystems is required to identify processes hindering natural recovery after disturbances and to set priorities on the areas and ecosystem components to be restored.     

Genetic costructure in a meta‐community under threat of habitat fragmentation

Habitat fragmentation increasingly threatens the services provided by natural communities and ecosystem worldwide. An understanding of the eco‐evolutionary processes underlying fragmentation‐compromised communities in natural settings is lacking, yet critical to realistic and sustainable conservation. Through integrating the multivariate genetic, biotic and abiotic facets of a natural community module experiencing various degrees of habitat fragmentation, we provide unique insights into the processes underlying community functioning in real, natural conditions. The focal community module comprises a parasitic butterfly of conservation concern and its two obligatory host species, a plant and an ant. We show that both historical dispersal and ongoing habitat fragmentation shape population genetic diversity of the butterfly Phengaris alcon and its most limited host species (the plant Gentiana pneumonanthe). Genetic structure of each species was strongly driven by geographical structure, altitude and landscape connectivity. Strikingly, however, was the strong degree of genetic costructure among the three species that could not be explained by the spatial variables under study. This finding suggests that factors other than spatial configuration, including co‐evolutionary dynamics and shared dispersal pathways, cause parallel genetic structure among interacting species. While the exact contribution of co‐evolution and shared dispersal routes on the genetic variation within and among communities deserves further attention, our findings demonstrate a considerable degree of genetic parallelism in natural meta‐communities. The significant effect of landscape connectivity on the genetic diversity and structure of the butterfly also suggests that habitat fragmentation may threaten the functioning of the community module on the long run.     

Lags in the response of mountain plant communities to climate change

Rapid climatic changes and increasing human influence at high elevations around the world will have profound impacts on mountain biodiversity. However, forecasts from statistical models (e.g. species distribution models) rarely consider that plant community changes could substantially lag behind climatic changes, hindering our ability to make temporally realistic projections for the coming century. Indeed, the magnitudes of lags, and the relative importance of the different factors giving rise to them, remain poorly understood. We review evidence for three types of lag: “dispersal lags” affecting plant species’ spread along elevational gradients, “establishment lags” following their arrival in recipient communities, and “extinction lags” of resident species. Variation in lags is explained by variation among species in physiological and demographic responses, by effects of altered biotic interactions, and by aspects of the physical environment. Of these, altered biotic interactions could contribute substantially to establishment and extinction lags, yet impacts of biotic interactions on range dynamics are poorly understood. We develop a mechanistic community model to illustrate how species turnover in future communities might lag behind simple expectations based on species’ range shifts with unlimited dispersal. The model shows a combined contribution of altered biotic interactions and dispersal lags to plant community turnover along an elevational gradient following climate warming. Our review and simulation support the view that accounting for disequilibrium range dynamics will be essential for realistic forecasts of patterns of biodiversity under climate change, with implications for the conservation of mountain species and the ecosystem functions they provide.     

Environmental filtering affects soil fungal community composition more than dispersal limitation at regional scales

The relative importance of dispersal limitation versus environmental filtering for community assembly has received much attention for macroorganisms. These processes have only recently been examined in microbial communities. Instead, microbial dispersal has mostly been measured as community composition change over space (i.e., distance decay). Here we directly examined fungal composition in airborne wind currents and soil fungal communities across a 40 000 km² regional landscape to determine if dispersal limitation or abiotic factors were structuring soil fungal communities. Over this landscape, neither airborne nor soil fungal communities exhibited compositional differences due to geographic distance. Airborne fungal communities shifted temporally while soil fungal communities were correlated with abiotic parameters. These patterns suggest that environmental filtering may have the largest influence on fungal regional community assembly in soils, especially for aerially dispersed fungal taxa. Furthermore, we found evidence that dispersal of fungal spores differs between fungal taxa and can be both a stochastic and deterministic process. The spatial range of soil fungal taxa was correlated with their average regional abundance across all sites, which may imply stochastic dispersal mechanisms. Nevertheless, spore volume was also negatively correlated with spatial range for some species. Smaller volume spores may be adapted to long-range dispersal, or establishment, suggesting that deterministic fungal traits may also influence fungal distributions. Fungal life-history traits may influence their distributions as well. Hypogeous fungal taxa exhibited high local abundance, but small spatial ranges, while epigeous fungal taxa had lower local abundance, but larger spatial ranges. This study is the first, to our knowledge, to directly sample air dispersal and soil fungal communities simultaneously across a regional landscape. We provide some of the first evidence that soil fungal communities are mostly assembled through environmental filtering and experience little dispersal limitation.     

Local and Regional Processes in Community Assembly

Controversy on whether local (deterministic) or regional (stochastic) factors control the structure of communities persists after decades of research. The main reason for why it has not been resolved may lie in the nature of evidence which largely comes from realized natural communities. In such communities assembly history leaves a mark that may support either set of factors. To avoid the confounding effects of assembly history we controlled for these effects experimentally. We created a null community by mixing 17 rock pool communities. We then divided the null community into replicates and distributed among treatments representing a gradient of factors from local to regional. We hypothesized that if deterministic factors dominate the assembly of communities, community structures should show a corresponding gradient from being very similar and convergent to dissimilar and divergent. In contrast, if local processes are predominantly stochastic in nature, such a gradient of community configurations should emerge even in the homogeneous setting. Our results appear to partially support both hypotheses and thus suggest that both deterministic and stochastic processes contribute to the assembly of communities. Furthermore, we found that to satisfactorily explain patterns observed in natural communities environmental heterogeneity and regional processes must also be considered. In conclusion, although deterministic mechanisms seem to be important in the assembly of communities, in natural systems their signal may be diluted and masked whenever other factors exert meaningful influence. Such factors increase the number of possible paths to the point that the number of paths equals the number of communities in a metacommunity.     

Global environmental change effects on ecosystems: the importance of land‐use legacies

One of the major challenges in ecology is to predict how multiple global environmental changes will affect future ecosystem patterns (e.g. plant community composition) and processes (e.g. nutrient cycling). Here, we highlight arguments for the necessary inclusion of land‐use legacies in this endeavour. Alterations in resources and conditions engendered by previous land use, together with influences on plant community processes such as dispersal, selection, drift and speciation, have steered communities and ecosystem functions onto trajectories of change. These trajectories may be modulated by contemporary environmental changes such as climate warming and nitrogen deposition. We performed a literature review which suggests that these potential interactions have rarely been investigated. This crucial oversight is potentially due to an assumption that knowledge of the contemporary state allows accurate projection into the future. Lessons from other complex dynamic systems, and the recent recognition of the importance of previous conditions in explaining contemporary and future ecosystem properties, demand the testing of this assumption. Vegetation resurvey databases across gradients of land use and environmental change, complemented by rigorous experiments, offer a means to test for interactions between land‐use legacies and multiple environmental changes. Implementing these tests in the context of a trait‐based framework will allow biologists to synthesize compositional and functional ecosystem responses. This will further our understanding of the importance of land‐use legacies in determining future ecosystem properties, and soundly inform conservation and restoration management actions.     

Distinct patterns of soil bacterial and fungal community assemblages in subtropical forest ecosystems under warming

Climate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co-occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.     

Ecosystem functions in degraded riparian forests of southeastern Kenya

Species community structures shape ecosystem functions, which are mostly stronger pronounced in intact than in degraded environments. Riparian forests in semiarid Africa provide important habitats for endangered plant and animal species and provide various ecosystem functions, that is, services to people settling along these streams. Most of these riparian forests are severely disturbed by human activities and dominated by invasive exotic plant species in the meanwhile. Thus, ecosystem functions are negatively influenced. While most studies have analyzed a specific metric to measure the degree of ecosystem function, little is known about how strongly different ecosystem functions respond to anthropogenic disturbances in parallel. In this study, we analyzed a set of four proxies of ecosystem functions, ground‐dwelling arthropod abundances, pollination, seed dispersal, and predation, along a highly disturbed riparian forest in southeastern Kenya. We assessed the land cover and land use manually and with an Unmanned Aerial Vehicle. Our data show that ecosystem functions respond differently to vegetation cover, human disturbances, and the availability of the invasive exotic shrub Lantana camara. The occurrence of representatives from the groups Saltatoria and Formicidae profits from heterogeneous habitat structures and natural riparian forest, while representatives of the Araneae profit from high proportion of agricultural fields. In general, predation is higher in mixed land use and natural riparian forest, while pollination and seed dispersal showed no significant trend in regard on land coverage. Along with this, predation also increased with rising proportion of natural riparian forest, while the proportion of agricultural land negatively affects predation, but in parallel showed a slightly significant positive trend with seed dispersal. Human disturbances and the occurrence of the invasive exotic L. camara shrub did not significantly affect our metrics of ecosystem functioning, except of the negative impact of human disturbances on pollinators. In conclusion, our results underpin that ecosystem functions respond highly variable and individually to environmental changes.     

Metacommunities of spiders in grassland habitat fragments of an agricultural landscape

Arthropod communities in fragmented agricultural landscapes depend on local processes and the interactions between communities in the habitat islands. We aimed to study metacommunity structure of spiders, a group that is known for high dispersal power, local niche partitioning and for engaging in species interactions. While living in fragmented habitats could lead to nestedness, other ecological traits of spiders might equally lead to patterns dominated either by species interactions or habitat filtering. We asked, which community pattern will prevail in a typical agricultural landscape with isolated patches of semi-natural habitats. Such a situation was studied by sampling spiders in 28 grassland locations in a Hungarian agricultural landscape. We used the elements of metacommunity structure (EMS) framework to distinguish between alternative patterns that reveal community organization. The EMS analysis indicated coherent species ranges, high turnover and boundary clumping, suggesting Clementsian community organization. The greatest variation in species composition was explained by local habitat characteristics, indicating habitat filtering. The influence of dispersal could be detected by the significant effect of landscape composition, which was strongest at 500 m. We conclude that dispersal allows spiders to respond coherently to the environment, creating similar communities in similar habitats. Consistent habitat differences, such as species rich versus species poor vegetation, lead to recognisably different, recurrent communities. These characteristics make spiders a predictable and diverse source of natural enemies in agricultural landscapes. Sensitivity to habitat composition at medium distances warns us that landscape homogenization may alter these metacommunity processes.     

Changes in assembly processes in soil bacterial communities following a wildfire disturbance

Although recent work has shown that both deterministic and stochastic processes are important in structuring microbial communities, the factors that affect the relative contributions of niche and neutral processes are poorly understood. The macrobiological literature indicates that ecological disturbances can influence assembly processes. Thus, we sampled bacterial communities at 4 and 16 weeks following a wildfire and used null deviation analysis to examine the role that time since disturbance has in community assembly. Fire dramatically altered bacterial community structure and diversity as well as soil chemistry for both time-points. Community structure shifted between 4 and 16 weeks for both burned and unburned communities. Community assembly in burned sites 4 weeks after fire was significantly more stochastic than in unburned sites. After 16 weeks, however, burned communities were significantly less stochastic than unburned communities. Thus, we propose a three-phase model featuring shifts in the relative importance of niche and neutral processes as a function of time since disturbance. Because neutral processes are characterized by a decoupling between environmental parameters and community structure, we hypothesize that a better understanding of community assembly may be important in determining where and when detailed studies of community composition are valuable for predicting ecosystem function.     

Invasive species and climate change: <Emphasis Type="Italic">Conyza canadensis</Emphasis> (L.) Cronquist as a tool for assessing the invasibility of natural plant communities along an aridity gradient

The predicted reduction in precipitation in the eastern Mediterranean due to climate change may expose the natural plant communities to invasive species. We assessed whether natural plant communities along an aridity gradient in Israel were resistant to invasion by considering differences in abiotic conditions and community characteristics in these regions. We considered Conyza canadensis as a model plant as it is a common invader in the region. We examined the mechanisms and functional traits of both the plant communities and C. canadensis that promote or discourage invasion. Study sites represented a rainfall gradient with four ecosystem types: mesic Mediterranean, Mediterranean, semiarid and arid. Our results showed that the mechanisms of community invasion resistance varied along the aridity gradient. At the arid and semiarid sites, water deficiency impaired the establishment of C. canadensis. At the mesic Mediterranean site, plant competition had a negative effect on C. canadensis performance, thus greatly reducing the likelihood of its establishment. We conclude that a decrease in regional precipitation due to climate change may not affect intrinsic resistance characteristics of natural plant communities to invasion in the area.