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We review the need for increasing agricultural sustainability, how this can in part be delivered by positive biodiversity–ecosystem function (BEF) effects, the role within these of plant–plant facilitation, and how a better understanding of this role may help to deliver sustainable crop (particularly arable) production systems.Major challenges facing intensive arable production include overall declines in biodiversity, poor soil structure and health, nutrient and soil particle run‐off, high greenhouse gas emissions, and increasing costs of synthetic inputs including herbicides, pesticides and fertilisers.Biodiversity–ecosystem function effects have the potential to deliver win–wins for arable food production, whereby enhanced biodiversity is associated with 'good outcomes' for farming sustainability, albeit sometimes through negative BEF effects for some components of the system. Although it can be difficult to separate explicitly from niche differentiation, evidence indicates facilitation can be a key component of these BEF effects.Explicit recognition of facilitation's role brings benefits to developing sustainable crop systems. First, it allows us to link fundamental ecological studies on the evolution of facilitation to the selection of traits that can enhance functioning in crop mixtures. Second, it provides us with analytical frameworks which can be used to bring structure and testable hypotheses to data derived from multiple (often independent) crop trials.Before concrete guidance can be provided to the agricultural sector as to how facilitation might be enhanced in crop systems, challenges exist with respect to quantifying facilitation, understanding the traits that maximise facilitation and integrating these traits into breeding programmes, components of an approach we suggest could be termed 'Functional Ecological Selection'.Synthesis. Ultimately, better integration between ecologists and crop scientists will be essential in harnessing the benefits of ecological knowledge for developing more sustainable agriculture. We need to focus on understanding the mechanistic basis of strong facilitative interactions in crop systems and using this information to select and breed for improved combinations of genotypes and species as part of the Functional Ecological Selection approach. [ABSTRACT FROM AUTHOR]

When plants compete what influences that interaction? To answer this we measured belowground competition directly, as the simultaneous capture of soil ammonium and nitrate by co‐existing herbaceous perennials, Dactylis glomerata and Plantago lanceolata, under the influence of: species identity; N uptake and biomass of focal and neighbour plants; location (benign lowland versus harsher upland site); N availability (low or high N fertilizer); N ion, ammonium or nitrate production (mineralisation) rate, and competition type (intra‐ or interspecific), as direct effects or pairwise interactions in linear models. We also measured biomass as an indirect proxy for competition. Only three factors influenced both competitive N uptake and biomass production: focal species identity, N ion and the interaction between N ion and neighbour N uptake. Location had little effect on N uptake but a strong influence on biomass production. N uptake increased linearly with biomass only in isolated plants. Our results support the view that measuring resource capture or biomass production tells you different things about how competitors interact with one another and their environment, and that biomass is a longer‐term integrative proxy for the outcomes of multiple separate interactions—such as competition for N—occurring between plants. We tested which of many factors had the strongest effects on competition for nitrogen, and if the same factors influenced competitors' growth. Different factors influenced competition and growth. For complete understanding of plant "competition" more than just biomass responses must be measured. [ABSTRACT FROM AUTHOR]

• Bryological records and Ellenberg values were combined as Ecosystem Health Indicators. • We analysed change across Scotland (1960–2016) for each 10 km × 10 km grid square. • Ellenberg Nitrogen (N) showed a humped relationship indicating recent recovery. • Increasing trends were evident for January and July Temperature. • Bryological records can form the basis of an effective Ecosystem Health Indicator. Environmental policy decisions should be based on robust indicators of changes in the environment. In Scotland these have been formalised as Ecosystem Health Indicators. Indicators work best where there is a direct link between what is measured and environmental change; changes in indices of species diversity or abundance provide alerts to environmental change but do not in themselves provide evidence of mechanisms. An alternative approach is to replace species occurrence data with species habitat or attribute values to create an indicator that links changes in species occurrences to environmental drivers. A series of indicators based on biological recording data, Ellenberg habitat preference values and mean climate niche was created by taking all records for bryophytes in Scotland (522187 records, 1960–2016) and analysing changes in mean attribute values through time for each 10 km × 10 km grid square. The resulting mean attribute values were analysed at the country level and showed clear quadratic (humped) trends for Ellenberg Nitrogen (N) and Reaction (R), an index of environmental acidity. There are linear decreasing trends for Ellenberg Light (L) and Precipitation, and linear increasing trends for January and July Temperature. Ellenberg Moisture (F) showed a clear trend, but it was not interpretable and appeared influenced by recording effort. Disaggregating to region was partly successful, but reduced samples sizes meant that for many regions the national trend was not significant. Ellenberg N and the two Temperature indices appear to be useful indicators as they are interpretable and performed better in the downscaling. Changes in L were also interpretable, but it performed poorly in downscaling to regional values. Ellenberg R appeared to be driven by changes in N as the two values are highly correlated across species. The downward trend in Precipitation ran counter to increases in rainfall suggesting that temperature driven evaporation is more likely to be driving changes in bryophyte distribution and whilst the indicator performed well it is difficult to explain to non-experts. Opportunistically collected data, like plant records, have great potential to be employed as indicators, especially as citizen scientists are involved and state resources can be used for data archiving and analysis. Also, conversion to attribute values removes many of the biases brought by differences in recorder effort and it directly links changes in species occurrences to environmental drivers. [ABSTRACT FROM AUTHOR]

Mathematical tools for quantifying plant–plant interactions are continuously improving, for example by attaining desirable statistical properties such as symmetry around zero (positive and negative effects have the same distribution). Standardisation is another such important property, making indices comparable between independent experiments, and can be achieved by standardisation for size. Using simulated data, here we show that an approach to standardisation by size that works well for indices of intensity is not appropriate for those of importance (intensity indices measure the absolute size of interaction effect, whilst importance indices quantify this effect as a proportion of the impact of the environment overall); our analyses also show that importance values can be overestimated in unproductive environments. These issues arise because importance indices use a reference value that is the "maximum growth on the gradient". This causes problems when comparing the results from studies that examine different sections of an environmental gradient: the maximum growth of plants within these sections is different and so the indices are not easy to compare between different sections of a gradient. Although this may sound like an obvious point, such issues can often be overlooked and a general solution adopted. One such solution is to report raw data from separate studies so that values can be recomputed for combined datasets and thus standardised comparisons. Another solution is to use an off‐gradient reference that is the maximum growth measured under optimal conditions for a model target species (phytometer). We analysed existing models that quantify importance of plant–plant interactions on ecological gradients. These models produce local values of importance that are not standardisable and overestimate facilitation. Using an off‐gradient reference of target plant performance, that will exceed or at least be equal to the highest target plant performance at any point of a gradient, can solve the above problems. [ABSTRACT FROM AUTHOR]

Abstract: Assisted colonisation, one form of species translocation, has been proposed as a tool for helping species to track suitable conditions in a changing climate. There are considerable practical challenges associated with it, including predicting where to place translocated individuals. This problem may be particularly big for small and immobile species, where small‐scale microenvironmental conditions de‐couple them from environmental conditions as projected in large‐scale climate models. To investigate this problem, we developed a survey‐based model to predict the occurrence of our target species, the fruticose terricolous arctic‐alpine lichen, Flavocetraria nivalis, within the Cairngorm Mountains. We then undertook an experimental translocation of this species. A second model, using variables that were significant in the survey‐based model, was only fair at predicting the initial pattern of survival at the recipient site. However, model fit of the translocation survival model improved over time as the distribution of surviving individuals more accurately reflected the distribution of suitable environmental conditions. In addition, model predictive power increased with the addition of data on microclimatic conditions at recipient plots. Synthesis and applications. Our results demonstrate that, for species which respond strongly to local environmental conditions, are immobile and, to some extent, decoupled from larger scale climates, it may be difficult to build a priori accurate predictive models of habitat suitability. In these cases, a combination of modelling and expert judgement, along with the movement of substantial numbers of transplants, may be the appropriate options for maximising the success of assisted colonisation. [ABSTRACT FROM AUTHOR]

Background: Intensive farming affects farmland biodiversity, and some arable plants in particular. Increasing crop genetic diversity can increase crop productivity or resilience and could also benefit rare arable plants. Aims: We examined whether barley presence, sowing density and genetic diversity impacted the rare plant Valerianella rimosa and explored possible underlying mechanisms. Methods: In a field study near Dundee, Scotland, we sowed plots of five single barley genotypes, and all five genotypes combined, at three densities; we also had barley-free plots. Valerianella seeds were sown into half of all plots. Measured responses included early-season cover and harvest biomass of barley and common weeds, abiotic parameters (soil moisture, light) and establishment, biomass and seed production by V. rimosa. Results: Barley presence promoted V. rimosa establishment early in the growing season, but without barley density or genetic diversity effects. By harvest, the impact of barley presence on V. rimosa abundance was lost; there were no effects on Valerianella seed production. Barley negatively impacted common weeds, but V. rimosa did not benefit from any indirect facilitation by barley, being bigger without barley. Conclusions: Early beneficial effects of barley on V. rimosa abundance appear offset by late-season competition. However, limited impacts of barley on V. rimosa reproductive success, and negative impacts on common weeds, indicate crops might play a role in conservation management of rare arable plants by creating space in the weed community. [ABSTRACT FROM AUTHOR]

Food security is currently considered a major global problem. However, increasing intensity of food production in agricultural systems has driven reductions in farmland biodiversity. A major challenge is to enable biodiversity conservation whilst addressing the problem of food security., Here we describe how facilitative plant-plant interactions in crop systems could be used to help strike this balance. An obvious example is that of intercropping systems, where combinations of crop species can - under some circumstances - deliver reduced inputs of agrochemicals (fertilizers, pesticides) per unit yield, with potential knock-on benefits for biodiversity conservation., Other facilitative processes can also play a role in biodiversity conservation. Increased intraspecific crop genetic diversity can help protect crops from pests and diseases. Although overlooked in facilitation research, we argue that the mechanisms operate in a manner which is directly analogous to associational defence against herbivores, a process well recognized in the facilitation literature. As with intercropping, the benefits to nature conservation arise from reduced pesticide use per unit harvested crop., Crops may have facilitative effects on some arable weed species, particularly those that are currently considered rare in intensive farming systems. Work is in its early stages to understand the underlying mechanisms, but it appears that crops might create niche space to which some weed species are adapted. Increasing plant species diversity through niche space creation may then have cascading benefits for other components of farmland biodiversity., Our new understanding of facilitative processes arising from work on crop systems has lessons for the study of facilitative interactions in natural and semi-natural communities. We argue that, although easier to identify and quantify in crop systems, some of these facilitative processes have to date been overlooked in studies of non-crop systems and certainly deserve further consideration., Finally, we discuss what steps may be needed to move from our understanding of the role of facilitation to the development of new agricultural practice. In some cases the challenge may be one of the encouraging uptake of existing practices, and in others more research is needed to understand how new ecological understanding might deliver more sustainable agricultural practice. [ABSTRACT FROM AUTHOR]

Direct and indirect interactions among plants contribute to shape community composition through above- and belowground processes. However, we have not disentangled yet the direct and indirect soil and canopy effects of dominants on understorey species. We addressed this issue in a semi-arid system from southeast Spain dominated by the legume shrub Retama sphaerocarpa. During a year with an exceptionally dry spring, we removed the shrub canopy to quantify aboveground effects and compared removed-canopy plots to open plots between shrubs to quantify soil effects, both with and without watering. We added a grass removal treatment in order to separate direct from indirect shrub effects and quantified biomass, abundance, richness and composition of the forb functional group. With watering, changes in forb biomass were primarily driven by indirect shrub effects, with contrasting negative soil and positive aboveground indirect effects; changes in forb abundance and composition were more influenced by direct shrub soil effects with contrasting species composition between open and Retama patches. As community composition was different between open and Retama patches the indirect effects of Retama on forb species did not concern forbs from the open community but forbs from Retama patches. Indirect effects are, thus, important at the functional group level rather than at the species level. Without watering, there were no significant interactions. Changes in species richness between treatments were weak and seldom significant. We conclude that shrub effects on understorey forbs are primarily due to their influence on soil properties, directly affecting forb species composition but indirectly affecting the biomass of the forbs of the Retama patches, and only with sufficient water. [ABSTRACT FROM AUTHOR]

Intercropping is a farming practice involving two or more crop species, or genotypes, growing together and coexisting for a time. On the fringes of modern intensive agriculture, intercropping is important in many subsistence or low-input/resource-limited agricultural systems. By allowing genuine yield gains without increased inputs, or greater stability of yield with decreased inputs, intercropping could be one route to delivering 'sustainable intensification'. We discuss how recent knowledge from agronomy, plant physiology and ecology can be combined with the aim of improving intercropping systems. Recent advances in agronomy and plant physiology include better understanding of the mechanisms of interactions between crop genotypes and species - for example, enhanced resource availability through niche complementarity. Ecological advances include better understanding of the context-dependency of interactions, the mechanisms behind disease and pest avoidance, the links between above- and below-ground systems, and the role of microtopographic variation in coexistence. This improved understanding can guide approaches for improving intercropping systems, including breeding crops for intercropping. Although such advances can help to improve intercropping systems, we suggest that other topics also need addressing. These include better assessment of the wider benefits of intercropping in terms of multiple ecosystem services, collaboration with agricultural engineering, and more effective interdisciplinary research. [ABSTRACT FROM AUTHOR]

Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a 'safety net' sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change. [ABSTRACT FROM AUTHOR]

The article discusses the study of competition among plants, with a focus on the dynamics of plant diversity in plant ecology. Topics include the use of biomass as a measure of competitive processes, the interpretation of dynamic interactions between plants through direct measurements of competitive mechanisms, and the ecological role of competition.

Abstract: The spatial pattern of plant communities can be an indicator of the processes that regulate community structure and their interplay with environmental drivers such as climate. However, to exploit such indicators we need a fuller understanding of the links between spatial pattern and climate. We examined variation in spatial pattern of annuals/biennials and perennials in a range margin steppic plant community in Germany over 26 years. We assessed change in spatial pattern through time, and how this change was related to local variation in climate and community composition. We found increasing dissociation between annuals/biennials and perennials through time, and a response of spatial pattern to summer temperature and precipitation. These responses are associated with the occurrence of Centaurea stoebe, a species which establishes in the community mid-way through the recording period. Our results indicate that in some circumstances spatial patterning of vegetation may not be directly linked to environmental severity, and that species turnover rather than changes in the interactions or abundance of species already in the community can influence the observed dynamics of vegetation spatial pattern. Thus, they support calls for a better understanding of the context-specificity of plant–plant interactions, their translation to spatial pattern, and their regulation by climate and other drivers such as species turnover. [Copyright &y& Elsevier]

Although rarely acknowledged, our understanding of how competition is modulated by environmental drivers is severely hampered by our dependence on indirect measurements of outcomes, rather than the process of competition. To overcome this, we made direct measurements of plant competition for soil nitrogen (N). Using isotope pool-dilution, we examined the interactive effects of soil resource limitation and climatic severity between two common grassland species. Pool-dilution estimates the uptake of total N over a defined time period, rather than simply the uptake of 15N label, as used in most other tracer experiments. Competitive uptake of N was determined by its available form (NO3 - or NH4 +). Soil N availability had a greater effect than the climatic conditions (location) under which plants grew. The results did not entirely support either of the main current theories relating the role of competition to environmental conditions. We found no evidence for Tilman's theory that competition for soil nutrients is stronger at low, compared with high nutrient levels and partial support for Grime's theory that competition for soil nutrients is greater under potentially more productive conditions. These results provide novel insights by demonstrating the dynamic nature of plant resource competition. [ABSTRACT FROM AUTHOR]

The article presents a comment on the proposed disintegration of the local-community concept by R.E. Ricklefs. It mentions that the two arguments undertaken by Ricklefs put emphasis on community ecology but it does not any relevance in the disintegration of local communities. It states that Ricklefs criticize the concept of local-community and on the constrictive nature of the community concept. It notes that the local composition, function, and evolutionary dynamics are affected with the population processes made outside the local community. It also discusses that the production of different evolutionary trajectories in different environments are initiated by the natural selection of genetics-based interactions in a community.

1. Here we present an introduction to this issue’s Special Feature arising from the British Ecological Society Symposium: Facilitation in Plant Communities (20–22 April 2009). 2. Papers in the Special Feature demonstrate the benefits that arise from cross-system application of general concepts, for example, the well-known stress gradient hypothesis. Such comparisons challenge our definition of facilitation, as well as our pre-conceptions on the nature of intermediary organisms. 3. We suggest that under some circumstances a clear definition of the two-way nature of interactions is essential, e.g. when considering the evolutionary implications of facilitation. In other cases, however, we can perhaps be more relaxed, e.g. when facilitation is a component of conservation ecology. 4. Synthesis. Overall we believe that establishing facilitation as an independent concept has driven substantial progress towards a clearer understanding of how ecological systems work. Through the links established by work such as that presented in this Special Feature, we believe this field will continue to make rapid progress and aid ecological understanding in general. [ABSTRACT FROM AUTHOR]

Abstract: Trees have a key role in determining the composition of soil biota via both above and belowground resource-based mechanisms, and by altering abiotic conditions. We conducted an outdoor mesocosm experiment to investigate the relative impact of above and belowground tree inputs on soil nematode trophic composition, and examine whether tree-driven impacts differed between contrasting species (birch and pine). For both species, we created a factorial design of litter addition and root presence treatments. The litter addition treatment was equivalent to natural levels of litterfall; tree saplings were planted in mesocosms for the root presence treatment and an unplanted control treatment was established that had no litter or root inputs. Litter addition had a limited impact on soil nematode community composition: it primarily decreased omnivore and predatory nematode abundance in birch but had few other effects on the nematode community. By contrast, root presence markedly altered nematode community composition through changes in a range of trophic groups. For both birch and pine, there were significant increases in total, fungivore and predatory nematode abundance in root presence treatments, and furthermore, total and fungivore abundances were positively related to root biomass. Root presence of these contrasting tree species also had a distinctive impact on some specific nematode trophic groups; pine roots promoted bacterivore abundance while birch roots promoted root-hair feeding nematode abundance. These findings suggest strong bottom-up effects of belowground tree inputs, and indicate that particular components of the nematode community may be affected differently by resource quantity and quality. Consequently, we suggest that, in the short-term, belowground rather than aboveground tree inputs have a strong impact on soil food web structure and complexity. [Copyright &y& Elsevier]

Questions: (1) Is climate a strong driver of vegetation dynamics, including interannual variation, in a range margin steppic community? (2) Are there long-term trends in cover and species richness in this community, and are these consistent across species groups and species within groups? (3) Can long-term trends in plant community data be related to variation in local climate over the last three decades? Location: A range margin steppic grassland community in central Germany. Methods: Cover, number and size of all individuals of all plant species present in three permanent 1-m² plots were recorded in spring for 26 years (1980-2005). Climatic data for the study area were used to determine the best climatic predictor for each plant community, functional group and species variable (annual data and interannual variation) using best subsets regression. Results: April and autumn temperature showed the highest correlation with total cover and species richness and with interannual variations of cover and richness. However, key climate drivers differed between the five most abundant species. Similarly, total cover and number and cover of perennials significantly decreased over time, while no trend was found for the cover and number of annuals. However, within functional groups there were also contrasting species-specific responses. Long-term temperature increases and high interannual variability in both temperature and precipitation were strongly related to long-term trends and interannual variations in plant community data. Conclusions: Temporal trends in vegetation were strongly associated with temporal trends in climate at the study site, with key roles for autumn and spring temperature and precipitation. Dynamics of functional groups and species within groups and their relationships to changes in temperature and precipitation reveal complex long-term and interannual patterns that cannot be inferred from short-term studies with only one or a few individual species. Our results also highlight that responses detected at the functional group level may mask contrasting responses within functional groups. We discuss the implications of these findings for attempts to predict the future response of biodiversity to climate change. [ABSTRACT FROM AUTHOR]

1. Numerous approaches have been taken to analysing the relationship between plant interactions and environmental severity. Considerable debate surrounds this relationship and its implications for the evolution of plant strategies and traits. This debate is commonly associated with the names of two of its main protagonists: Grime and Tilman. 2. However, because researchers often fail to make explicit the distinction between two concepts – the importance and intensity of competition – they perpetuate this debate. To illustrate this point we discuss a new approach to examining plant interactions across gradients proposed by Wilson. 3. We support the main thrust of Wilson's work – improving the information provided by interaction indices. However, we highlight what we believe to be an oversight in Wilson's Discussion: the proposal that his new indices can shed light on the Grime–Tilman debate. We argue that this is not possible as Wilson's indices measure competition intensity (competition's absolute impact), whereas Grime's theories relate to competition importance (competition's relative impact). 4. We support our argument through re-analysis of the data explored by Wilson, demonstrating that the relationships between competition importance, competition intensity, Wilson's new indices and biomass (a surrogate of productivity) are both complex and variable. 5. Wilson's discussion is part of a body of literature that overlooks the distinction between competition importance and intensity. We examine a number of other well-known studies, demonstrating how this oversight and associated confusion are widespread, may have originated with the concept's original source, and unnecessarily perpetuate debate. 6. Synthesis. The concepts of competition intensity and importance are central to resolving key ecological debates, but are still overlooked in contemporary research. Their uptake and careful application would greatly aid advances in plant ecology. [ABSTRACT FROM AUTHOR]

1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists. [ABSTRACT FROM AUTHOR]

Abstract: There is an urgent need for accurate prediction of climate change impacts on species ranges. Current reliance on bioclimatic envelope approaches ignores important biological processes such as interactions and dispersal. Although much debated, it is unclear how such processes might influence range shifting. Using individual-based modelling we show that interspecific interactions and dispersal ability interact with the rate of climate change to determine range-shifting dynamics in a simulated community with two growth forms—mutualists and competitors. Interactions determine spatial arrangements of species prior to the onset of rapid climate change. These lead to space-occupancy effects that limit the rate of expansion of the fast-growing competitors but which can be overcome by increased long-distance dispersal. As the rate of climate change increases, lower levels of long-distance dispersal can drive the mutualists to extinction, demonstrating the potential for subtle process balances, non-linear dynamics and abrupt changes from species coexistence to species loss during climate change. [Copyright &y& Elsevier]

Contents Summary I. Introduction 272 II. Plant–plant interactions mediate the impacts of environmental change 273 III. Plant–plant interactions in context 276 IV. Understanding variation in the role of plant–plant interactions 278 V. Concluding remarks 281 Acknowledgements 281 References 281 Natural systems are being subjected to unprecedented rates of change and unique pressures from a combination of anthropogenic environmental change drivers. Plant–plant interactions are an important part of the mechanisms governing the response of plant species and communities to these drivers. For example, competition plays a central role in mediating the impacts of atmospheric nitrogen deposition, increased atmospheric carbon dioxide concentrations, climate change and invasive nonnative species. Other plant–plant interaction processes are also being recognized as important factors in determining the impacts of environmental change, including facilitation and evolutionary processes associated with plant–plant interactions. However, plant–plant interactions are not the only factors determining the response of species and communities to environmental change drivers – their activity must be placed within the context of the wide range of factors that regulate species, communities and ecosystems. A major research challenge is to understand when plant–plant interactions play a key role in regulating the impact of environmental change drivers, and the type of role that plant–plant interactions play. Although this is a considerable challenge, some areas of current research may provide the starting point to achieving these goals, and should be pursued through large-scale, integrated, multisite experiments. [ABSTRACT FROM AUTHOR]

Plant communities have traditionally been viewed as either a random collection of individuals or as organismal entities. For most ecologists however, neither perspective provides a modern comprehensive view of plant communities, but we have yet to formalize the view that we currently hold. Here, we assert that an explicit re-consideration of formal community theory must incorporate interactions that have recently been prominent in plant ecology, namely facilitation and indirect effects among competitors. These interactions do not support the traditional individualistic perspective. We believe that rejecting strict individualistic theory will allow ecologists to better explain variation occurring at different spatial scales, synthesize more general predictive theories of community dynamics, and develop models for community-level responses to global change. Here, we introduce the concept of the integrated community (IC) which proposes that range from highly natural plant communities individualistic to highly interdependent depending on synergism among: (i) stochastic processes, (ii) the abiotic tolerances of species, (iii) positive and negative interactions among plants, and (iv) indirect interactions within and between trophic levels. All of these processes are well accepted by plant ecologists, but no single theory has sought to integrate these different processes into our concept of communities. [ABSTRACT FROM AUTHOR]

In the last decade, plant ecologists have focussed more on the occurrence of positive plant–plant interactions than ever before. Especially in severe environments, such as the Arctic, species removal experiments tend to find facilitative rather than competitive effects, casting doubt on the importance of competition under extreme growing conditions. Two approaches to measure plant–plant interactions presented here reveal that competition affects plant growth even in the high Arctic. Luzula confusa and Salix polaris show a reduced growth in mixed stands compared with pure. This competition effect is not detected in a removal experiment, which inevitably also alters site microclimate. Indeed, in the latter experiment, facilitative effects of Luzula on Salix were found. Evidently, both facilitation and competition are acting and important. Causes and implications are discussed using a conceptual model derived from that of . [Copyright &y& Elsevier]

Background and aims: Nutrient spatial heterogeneity occurs ubiquitously in soil, but its impact on plant growth and competition throughout the whole growth cycle remains unclear. We assessed the effects of different nutrient supply patterns and planting density on maize (Zea mays L.) growth rate, root competitive intensity and grain yield. Methods: Maize was grown with homogeneous or heterogeneous nutrient (ammonium and phosphorus) supplies under low and high planting densities in field conditions. Results: Nutrient patches promoted root proliferation and plant growth rate in the short term; however, with nutrient depletion and roots still proliferating in the patch zone, the plant growth rate was surpassed by that of plants in the homogeneous ammonium and phosphorus treatments with time. Consequently, final shoot biomass showed no difference between nutrient supply patterns at a given planting density. Furthermore, the temporal decoupling between root growth and soil nutrient availability induced greater competitive intensity in the heterogeneous than homogeneous treatments between the vegetative stage and anthesis. Under these conditions, heterogeneous ammonium and phosphorus supply markedly decreased grain yield at high planting density. Conclusions: Our results demonstrate that heterogeneous nutrient supply-induced root competition at high planting density modulates the dynamics of plant development and decreases final productivity. [ABSTRACT FROM AUTHOR]

Question What are the interacting effects of stress and disturbance on both competition and facilitation, and ultimately their impact on diversity and species ranges? Location Simulated data. Method We extended the spatially explicit model of Xiao et al. ( Oikos, 118, 2009, 1343) to consider how stress and disturbance - operating alone or together - affect species distributions through varying biotic interactions. Results In the absence of facilitation, species ranges only occurred within the limits of a triangular zone, which can be considered equivalent to Grime's C-S-R triangle. Competitive species were distributed in low stress and disturbance conditions. Stress- and disturbance-tolerant species occurred in more stressed and disturbed environments. Species richness followed a hump-shaped relationship with a hotspot of diversity occurring close to the centre of the C-S-R triangle. In contrast, facilitation was able to dampen the negative impacts of stress and disturbance acting either solely or simultaneously, but this influence was not simply the sum of the effects of the processes operating independently on the two environmental gradients. Facilitation extended species distributions along both the stress and disturbance gradients and displaced the hotspot of diversity into the centre of the response surface. Conclusions Facilitation was able to promote the occurrence and persistence of communities in highly stressed and disturbed conditions, i.e. allowing a stable community to exist beyond the limits of the C-S-R triangle. We also showed that facilitation can be an important mechanism driving the displacement of hotspots of diversity from benign toward intermediate stressed and disturbed environments. [ABSTRACT FROM AUTHOR]

Understanding how communities assemble is a key challenge in ecology. Conflicting hypotheses suggest that plant traits within communities should show divergence to reflect strategies to reduce competition or convergence to reflect strong selection for the environmental conditions operating. Further hypotheses suggest that plant traits related to productivity show convergence within communities, but those related to disturbance show divergence. Data on functional diversity (FD) of 12 traits from 30 communities ranging from arable fields, mown and grazed grasslands to moorland and woodland were employed to test this using randomisations tests and correlation and regression analysis. No traits showed consistent significant convergence or divergence in functional diversity. When correlated to measures of the environment, the most common pattern was for functional diversity to decline (7 out of 12 traits) and the degree of convergence (7 out of 12 traits) to increase as the levels of productivity (measured as primary productivity, soil nitrogen release and vegetation C:N) and disturbance increased. Convergence or a relationship between functional diversity and the environment was not seen for a number of important traits, such as LDMC and SLA, which are considered as key predictors of ecosystem function. The analysis indicates that taking into account functional diversity within a system may be a necessary part of predicting the relationship between plant traits and ecosystem function, and that this may be of particular importance within less productive and less disturbed systems. [ABSTRACT FROM AUTHOR]

Debate on the relationship between diversity and stability has been driven by the recognition that species loss may influence ecosystem properties and processes. We conducted a litterbag experiment in the Scottish Highlands, United Kingdom, to examine the effects of altering plant litter diversity on decomposition, microbial biomass, and microfaunal abundance. The design of treatments was fully factorial and included five species from an upland plant community (silver birch, Betula pendula; Scots' pine, Pinus sylvestris; heather, Calluna vulgaris; bilberry, Vaccinium myrtillus; wavy-hair grass, Deschampsiaflexuosa); species richness ranged from one to five species. We tested the effects of litter species richness and composition on variable means, whether increasing litter species richness reduced variability in the decomposer system, and whether any richness-variability relationships were maintained over time (196 vs. 564 days). While litter species composition effects controlled variable means, we revealed reductions in variability with increasing litter species richness, even after accounting for differences between litter types. These findings suggest that higher plant species richness per se may result in more stable ecosystem processes (e.g., decomposition) and decomposer communities. Negative richness-variation relationships generally relaxed over time, presumably because properties of litter mixtures became more homogeneous. However, given that plant litter inputs continue to enter the belowground system over time, we conclude that variation in ecosystem properties may be buffered by greater litter species richness. [ABSTRACT FROM AUTHOR]

Abstract: To determine whether successional changes in plant communities may influence belowground community structure, we quantified nematode abundance, trophic structure and diversity along two separate chronosequences from heather moorland to birch woodland in the Scottish uplands. Tree invasion markedly altered plant community composition, and hence litter inputs, both directly, and indirectly through changes in understorey species. In turn, these changes in detrital inputs were reflected in consistent changes in nematode community structure. Nematode abundance increased from moorland to birch woodland, with moorland soils being dominated by a few taxa, notably root-hair and fungal feeders, compared to the more diverse composition of the birch woodland soils. Trophic structure was altered through an increase in the abundance of bacterial feeding relative to fungal-feeding nematodes, and an increase in the abundance of predatory nematodes. The increase in predators during the succession from moorland to woodland was associated with an increase in soil pH, highlighting that not only changes in the plant community, but also changes in soil properties associated with tree invasion may influence soil nematodes. Nematode diversity increased from moorland to birch woodland, with nematode richness being positively related to both plant species richness and soil pH. These results suggest that trees may control soil community structure through the manipulation of resources and the soil physico-chemical environment, promoting greater nematode diversity and trophic complexity. [Copyright &y& Elsevier]

The impact of reduced light conditions as an indirect effect of nitrogen (N) deposition was determined on three mosses in a montane ecosystem, where sedge and grass cover increase due to N enrichment. Additionally, in the greenhouse we established the importance of low light to moss growth as an indirect N deposition effect relative to the direct toxic effects of N. The amount of light reaching the moss layer was strongly and negatively related to graminoid abundance. Mosses showed differing sensitivities to reduced light in the field.Racomitrium lanuginosumbiomass was found to be highest under high-light conditions,Polytrichum alpinumat intermediate light levels, whilst that ofDicranum fuscescenswas unrelated to light availability. Moreover,Racomitriumbiomass decreased with increasing amounts of graminoid litter, whereas the other species were little affected. All three mosses responded differently to the combination of elevated N (20 vs 10 kg N ha-1 year-1) and reduced light (60 and 80% reduction) in the greenhouse.Racomitriumgrowth was strongly influenced by both light reduction and elevated N, in combination reducing shoot biomass up to 76%. There was a tendency forDicranumgrowth to be modestly reduced by elevated N when shaded, causing up to 19% growth reduction.Polytrichumgrowth was not influenced by elevated N but was reduced up to 40% by shading. We conclude that competition for light, induced by vascular plants, can strongly influence moss performance even in unproductive low biomass ecosystems. The effects of reduced light arising from N pollution can be as important to mosses as direct toxicity from N deposition. Yet, different sensitivities of mosses to both toxic and shading effects of elevated N prevent generalisation and can lead to competitive species replacement within moss communities. This study demonstrates the importance of understanding moss-vascular plant interactions to allow interpretation and prediction of ecosystem responses to anthropogenic drivers such as atmospheric N deposition or climate change. [ABSTRACT FROM AUTHOR]

Biological diversity depends on multiple, cooccurring ecological interactions. However, most studies focus on one interaction type at a time, leaving community ecologists unsure of how positive and negative associations among species combine to influence biodiversity patterns. Using surveys of plant populations in alpine communities worldwide, we explore patterns of positive and negative associations among triads of species (modules) and their relationship to local biodiversity. Three modules, each incorporating both positive and negative associations, were overrepresented, thus acting as "network motifs." Furthermore, the overrepresentation of these network motifs is positively linked to species diversity globally. A theoretical model illustrates that these network motifs, based on competition between facilitated species or facilitation between inferior competitors, increase local persistence. Our findings suggest that the interplay of competition and facilitation is crucial for maintaining biodiversity. [ABSTRACT FROM AUTHOR]

As agriculture has intensified, many once-common wildflowers have declined in arable landscapes, which has widespread implications for associated ecosystem services. The incorporation of sustainable practices, for example, growing living mulches (in-field, non-crop plant ground cover, maintained during the target crop growing season), can boost arable biodiversity, but few wildflower species have been utilised in this context. Our aim was to determine the suitability of arable wildflower species, once considered weeds, for use as living mulches. We first screened a number of arable wildflower species for germination when growing with a common cereal, barley (Hordeum vulgare). We then grew two (Centaurea cyanus and Scandix pecten-veneris) in pots in a glasshouse with and without barley, and grew barley alone to test the impact of the wildflowers on barley growth and biomass. Neither of the wildflowers significantly negatively impacted barley biomass. Barley initially facilitated germination in S. pecten-veneris, but ultimately suppressed the above-ground biomass of both wildflowers. However, both wildflower species were able to coexist alongside barley. Our experiment provides evidence that wildflowers that were considered weeds in traditional agriculture have the potential to be grown alongside barley and could be incorporated as part of a living mulch. [ABSTRACT FROM AUTHOR]

• Scotland's natural capital is increasing but is still much lower than historically. • Large variations exist in the quality of different habitats in Scotland. • The NCAI is robust, credible and useful for policy making. • The NCAI has potential to be adapted by other regions and countries internationally. Understanding the contributions from the environment to society is seen as increasingly important globally. In Scotland this is currently a high priority, as policymakers begin to shift attention away from traditional wellbeing indicators such as GDP. Although alternative natural capital accounting techniques exist, and are useful for creating commeasurable market values, they are unable to account for the full suite of benefits derived from the environment. Scotland's Natural Capital Asset Index (NCAI) is an attempt to create an account of Scotland's natural capital stock and how it's potential to contribute to wellbeing changes on an annual basis. This paper describes the inputs, calculation process and results of the NCAI. It also reports on sensitivity testing of the model, which found the model to be robust, credible to policy makers and meaningful, thus achieving the overall aims of the indicator. [ABSTRACT FROM AUTHOR]

Invasive plant impacts vary widely across introduced ranges. We tested the hypothesis that differences in the eco‐evolutionary experience of native communities with the invader correspond with the impacts of invasive species on native vegetation, with impacts increasing with ecological novelty. We compared plant species richness and composition beneath Pinus contorta to that in adjacent vegetation and other P. contorta stands across a network of sites in its native (Canada and USA) and non‐native (Argentina, Chile, Finland, New Zealand, Scotland, Sweden) ranges. At sites in North America and Europe, within the natural distribution of the genus Pinus, P. contorta was not associated with decreases in diversity. In the Southern Hemisphere, where there are no native Pinaceae, plant communities beneath P. contorta were less diverse than in other regions and compared to uninvaded native vegetation. Effects on native vegetation were particularly pronounced where P. contorta was a more novel life form and exhibited higher growth rates. Our results support the hypothesis that the eco‐evolutionary experience of the native vegetation, and thus the novelty of the invader, determines the magnitude of invader impacts on native communities. Understanding the eco‐evolutionary context of invasions will help to better understand and predict where invasion impacts will be greatest and to prioritize invasive species management. [ABSTRACT FROM AUTHOR]

Temporal dynamism of plant resource capture, and its impacts on plant–plant interactions, can have important regulatory roles in multispecies communities. For example, by modifying resource acquisition timing, plants might reduce competition and promote their coexistence. However, despite the potential wide ecological relevance of this topic, short-term (within growing season) temporal dynamism has been overlooked. This is partially a consequence of historic reliance on measures made at single points in time. We propose that with current technological advances this is a golden opportunity to study within growing season temporal dynamism of resource capture by plants in highly informative ways. We set out here an agenda for future developments in this research field, and explore how new technologies can deliver this agenda. [ABSTRACT FROM AUTHOR]

Assessing effectiveness of international biodiversity targets requires long-term monitoring of species to identify changes in their abundance. Grasslands cover large areas of many countries, provide high levels of provisioning ecosystem services and are an important habitat for many species. While grasslands are often anthropogenic in nature, human-induced environmental perturbations are acknowledged threats to their biodiversity and functioning. Using a repeat survey of grassland plots in Scotland, UK we identified long-term changes in community composition and species indices over a 40 year period (1973–2013). Scottish grasslands were found to have changed significantly over this time. Species richness increased, while diversity declined as dominant species increased in cover. Nitrogen-demanding and moisture-requiring species increased, possibly reflecting increases in atmospheric nitrogen deposition and rainfall over this time. In Acid and Nardus grasslands species with low tolerance to very acidic soils increased, possibly reflecting a decrease in sulphur deposition. Overall β-diversity showed no change, indicating that contrary to trends in other habitats, homogenisation has not occurred. In general bryophytes and low-growing forb and grass species declined while taller species increased. This may reflect either the decline in grazing in recent years or the increase in atmospheric nitrogen deposition. Species richness increased but the majority of species declined in cover while a few dominant species increased suggesting that an extinction debt may be establishing. The trade-offs between increased management to reduce the extinction debt and abandonment with increased shrub cover which might be beneficial to other wildlife is discussed. [ABSTRACT FROM AUTHOR]

The article presents an introduction to a special section within the journal on the mechanisms of plant competition, with information on ecological studies of plant competition, models of plant ecology, and the effects of plant interactions on the local environment.

Understanding species coexistence and regulation of biodiversity are major research challenges, yet there is no consensus on the effects of diversity on diversity, including their mediation through plant-plant interactions., We examined how the diversity of recipient communities impacted on the establishment of colonising species. We ran a greenhouse-based community experiment, creating artificial arable crop communities with varying levels of barley genotype and weed species diversity, analysed with structural equation modelling of responses across trophic levels., Colonising arable weed species establishment was significantly reduced when the recipient communities' weed species richness, but not barley genotype richness, increased. Recipient plant communities with higher species richness occupied more total niche space and showed stronger competition with colonising species. In contrast, recipient plant communities with higher genotype richness, even though they had slightly greater niche space occupancy, had no significant effects on the colonisation of additional species., Responses were species specific: colonising common weed species establishment was less affected by the recipient plant communities than that of colonising rare weed species. Strong responses of colonising rare species were related to the abiotic rather than the biotic environment created by the recipient communities. The stronger response of colonising rare species suggests greater niche overlap with and competitive inferiority to the recipient plant community, whereas the relative independence of colonising common species indicates less niche overlap and/or competitive equality or superiority., We observed a negative species diversity effect on colonising species, with the effect size increasing with increasing rarity of the colonising species. This differential responsiveness of colonising rare and common arable weed species to the presence of and diversity in the recipient arable plant communities may be crucial in understanding rarity and may result from differential evolutionary pathways in response to interactions. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of community assembly may provide evidence to improve crop management, and in particular how weeds impact on crop yields. Focussing on plant functional traits and their diversity, we analysed a crop–weed interaction study with different levels of weed species and barley cultivar diversity to assess how weed species and barley cultivars respond to competition. Pre-emption of light resources by the taller barley did not impact on the weeds, with both weeds and barley showing similar order of magnitude shifts in height, specific leaf area and leaf dry matter content in response to crop–weed competition. These shifts were to a more conservative growth pattern, and suggest in this study a greater importance of below- than above-ground interactions in driving trait responses. The mixture of barley cultivars shifted the weeds to a more conservative growth pattern compared to the cultivar monocultures. The results indicate that cultivar mixtures could result in less need for weed control in arable fields, and possibly that the development of complementary cultivar mixtures could reinforce this effect. This confirms the results of other studies which show that mixtures either improve yields or make yields less variable in response to weed competition. [ABSTRACT FROM AUTHOR]

• Attributing biodiversity trends is necessary to take corrective action. • We link trends in bryophyte and lichen occupancy to indicator values. • Climate change, pollution and increased shade shifted species occupancy patterns. • Contrasting trends imply increased bryophytes competitive advantage over lichens. • Prevailing negative trends for lichens are concerning for Scottish biodiversity. The attribution of biodiversity trends to the action of individual drivers is a first step in developing strategies to conserve, enhance and restore that diversity. One approach to that identification is to link information on species trends with information on ecological preferences that relate to the drivers. Long-term and short-term occupancy trends for 326 bryophyte species (1972–2015 and 2005–2015, respectively) and 437 lichen species (1971–2015 and 2005–2015, respectively) for Scotland were linked with appropriate indicators to assess the action of specific drivers. Bryophyte species of heathlands and woodlands showed positive trends, whilst lichen species from these habitats showed negative trends. Bryophytes and lichens of drier habitats and locations tended to have more positive trends whilst those of wetter habitats tended to be negative. Similarly, evidence suggested that bryophytes and lichens of open areas had more negative trends than those of shadier habitats and that species from both groups of higher fertility habitats had more positive trends than those of less fertile ones. Bryophyte species from warmer areas tended to increase in range. Opposite trends for bryophytes and lichens in heathlands and woodlands suggest competition for space or opposite reactions to other drivers, but it is clear that they should not be lumped into a single functional grouping. There were clear trends for suggesting that increased temperatures (bryophytes only), cumulative nitrogen pollution and reduced land use intensity were shifting assemblages. The overall predominance of negative trends for lichens suggests that many species have lost habitat through decreasing light availability and increased dryness, and potentially through competition with bryophytes. Given the international importance of Scotland for both these groups, these trends for lichens are of concern. [ABSTRACT FROM AUTHOR]

Biodiversity regulates ecosystem functions such as productivity, and experimental studies of species mixtures have revealed selection and complementarity effects driving these responses. However, the impacts of intraspecific genotypic diversity in these studies are unknown, despite it forming a substantial part of the biodiversity., In a glasshouse experiment we constructed plant communities with different levels of barley ( Hordeum vulgare) genotype and weed species diversity and assessed their relative biodiversity effects through additive partitioning into selection and complementarity effects., Barley genotype diversity had weak positive effects on aboveground biomass through complementarity effects, whereas weed species diversity increased biomass predominantly through selection effects. When combined, increasing genotype diversity of barley tended to dilute the selection effect of weeds., We interpret these different effects of barley genotype and weed species diversity as the consequence of small vs large trait variation associated with intraspecific barley diversity and interspecific weed diversity, respectively. The different effects of intra- vs interspecific diversity highlight the underestimated and overlooked role of genetic diversity for ecosystem functioning. [ABSTRACT FROM AUTHOR]

Facilitative effects of some species on others are a major driver of biodiversity. These positive effects of a benefactor on its beneficiary can result in negative feedback effects of the beneficiary on the benefactor and reduced fitness of the benefactor. However, in contrast to the wealth of studies on facilitative effects in different environments, we know little about whether the feedback effects show predictable patterns of context dependence., We reanalyzed a global data set on alpine cushion plants, previously used to assess their positive effects on biodiversity and the nature of the beneficiary feedback effects, to specifically assess the context dependence of how small- and large-scale drivers alter the feedback effects of cushion-associated (beneficiary) species on their cushion benefactors using structural equation modelling., The effect of beneficiaries on cushions became negative when beneficiary diversity increased and facilitation was more intense. Local-scale biotic and climatic conditions mediated these community-scale processes, having indirect effects on the feedback effect. High-productivity sites demonstrated weaker negative feedback effects of beneficiaries on the benefactor., Our results indicate a limited impact of the beneficiary feedback effects on benefactor cushions, but strong context dependence. This context dependence may help to explain the ecological and evolutionary persistence of this widespread facilitative system. [ABSTRACT FROM AUTHOR]

Facilitative interactions are defined as positive effects of one species on another, but bidirectional feedbacks may be positive, neutral, or negative. Understanding the bidirectional nature of these interactions is a fundamental prerequisite for the assessment of the potential evolutionary consequences of facilitation., In a global study combining observational and experimental approaches, we quantified the impact of the cover and richness of species associated with alpine cushion plants on reproductive traits of the benefactor cushions., We found a decline in cushion seed production with increasing cover of cushion-associated species, indicating that being a benefactor came at an overall cost. The effect of cushion-associated species was negative for flower density and seed set of cushions, but not for fruit set and seed quality. Richness of cushion-associated species had positive effects on seed density and modulated the effects of their abundance on flower density and fruit set, indicating that the costs and benefits of harboring associated species depend on the composition of the plant assemblage., Our study demonstrates 'parasitic' interactions among plants over a wide range of species and environments in alpine systems, and we consider their implications for the possible selective effects of interactions between benefactor and beneficiary species. [ABSTRACT FROM AUTHOR]

Altitudinal gradients provide a useful space-for-time substitution to examine the capacity for plant competition and facilitation to mediate responses to climate change. Decomposing net interactions into their facilitative and competitive components, and quantifying the performance of plants with and without neighbours along altitudinal gradients, may prove particularly informative in understanding the mechanisms behind plant responses to environmental change., To decouple the inherent responses of species to climate from the responses of plant-plant interactions to climate, we conducted a meta-analysis. Using data from 16 alpine experiments, we tested if changes in net interactions along altitudinal gradients were due to a change in the performance of target species without neighbours (i.e. environmental severity effects only) or with neighbours (neighbour trait mediated effects)., There was a global shift from competition to facilitation with increasing altitude driven by both environmental severity and neighbour trait effects. However, this global pattern was strongly influenced by the high number of studies in mesic climates and driven by competition at low altitude in temperate climates (neighbour trait effect), and facilitation at high altitude in arctic and temperate climates (environmental severity effect)., In Mediterranean systems, there was no significant effect of competition, and facilitation increased with decreasing altitude. Changes in facilitation with altitude could not unambiguously be attributed to either neighbour trait effects or environmental severity effects, probably because of the opposing stress gradients of cold and aridity in dry environments., Partitioning net interactions along altitudinal gradients led to the prediction that climate change should decrease the importance of facilitation in mesic alpine communities, which might in turn exacerbate the negative effects of climate change in these regions. In xeric climates, the importance of facilitation by drought-tolerant species should increase at low altitudes which should mitigate the negative effect of climate change. However, the importance of facilitation by cold-tolerant species at high altitudes may decrease and exacerbate the effects of climate change. [ABSTRACT FROM AUTHOR]

Disturbance is one of the most important factors structuring the taxonomic and functional composition of vegetation. Vegetation resistance or resilience to disturbance depends on local environmental conditions, further modifying the pool of species and traits. This paper aims to understand how disturbance and local environment combine to affect the resistance and resilience of vegetation. A functional-trait approach was used to detect traits related to vegetation resistance and resilience, and trait attributes of individual species responding to disturbance. Trait approaches enable comparison of vegetation responses across biogeographic regions containing different species pools. At 35 European forest and grassland sites, experimental disturbance (human trampling) was applied at five intensities. Indices for resistance and resilience were calculated, based on total vegetation cover, and related to climate and local site factors. Additional indices were calculated for the most common species to demonstrate traits that confer resistance and resilience to disturbance. Vegetation resistance was related to occurrence of species with traits selected by a history of intensive land use (smaller leaf size, rosette plant form) and local environmental conditions. Vegetation resilience, however, was associated with ecosystem properties that facilitate higher growth rates. Resilient vegetation occurred where irradiation was higher (grasslands, open forests) with sufficient water availability (summer precipitation, humidity) and comprised of species with traits related to enhanced growth rates (increased specific leaf area, decreased leaf dry matter content). Synthesis. This pan-European disturbance experiment demonstrates that different drivers (land use or climate) of vegetation response show different mechanistic responses to physical disturbance. Resistance depends on the functional composition of predominant species in the assemblage, which is strongly affected by land-use history; resilience is directly connected to growth rates affected by climate. We argue for the inclusion of land-use history and climate into the planning process for visitor management, especially in areas of high conservation interest. [ABSTRACT FROM AUTHOR]

The evolutionary potential of populations is mainly determined by population size and available genetic variance. However, the adaptability of spatially structured populations may also be affected by dispersal: positively by spreading beneficial mutations across sub-populations, but negatively by moving locally adapted alleles between demes. We develop an individual-based, two-patch, allelic model to investigate the balance between these opposing effects on a population's evolutionary response to rapid climate change. Individual fitness is controlled by two polygenic traits coding for local adaptation either to the environment or to climate. Under conditions of selection that favour the evolution of a generalist phenotype (i.e. weak divergent selection between patches) dispersal has an overall positive effect on the persistence of the population. However, when selection favours locally adapted specialists, the beneficial effects of dispersal outweigh the associated increase in maladaptation for a narrow range of parameter space only (intermediate selection strength and low linkage among loci), where the spread of beneficial climate alleles is not strongly hampered by selection against non-specialists. Given that local selection across heterogeneous and fragmented landscapes is common, the complex effect of dispersal that we describe will play an important role in determining the evolutionary dynamics of many species under rapidly changing climate. [ABSTRACT FROM AUTHOR]

In this article the authors discusses aspects of the report "Productivity Is a Poor Predictor of Plant Species Richness" by Peter B. Adler and colleagues in the September 23, 2011 issue of "Science."