1.Predicting plant community assembly is challenging in part because the influence of environmental conditions via plant functional strategies and the relevance of mechanisms of community assembly change across habitats and these changes remain poorly studied.

A major challenge in ecological research is to identify the tolerance of ecological communities to external perturbations. Modern Coexistence Theory (MCT) has been widely adopted as a framework to investigate the tolerance to perturbations in relative reductions of per capita growth rates, often using metrics that explicitly eliminate the independent role of intrinsic growth rates. More recently, the Structural Approach (SA) was introduced to investigate the tolerance of communities to perturbations in intrinsic growth rates as a function of the strength of intraspecific and interspecific competition. Because the external perturbations are likely to happen in both intrinsic growth rates and competition strengths, no framework alone can fully disentangle the effects of external perturbations. Here we combine MCT and SA to disentangle the tolerance in coexistence and priority effects of a pair of competing species when subject to perturbations in intrinsic growth rates and competition strengths. Through this combination, we reveal the emergence of a key trade‐off: increasing the tolerance to perturbations in intrinsic growth rates typically decreases the tolerance in competition strengths, and vice versa. Furthermore, this trade‐off is stronger under coexistence than under priority effects. We test this combined framework on competing pairs of 18 California annual plant species. For both coexistence and priority effects, we find that the tolerance to perturbations in intrinsic growth rates is maximized instead of that to perturbations in competition strengths in the studied annual plant communities. Synthesis. Our combined framework of MCT and SA illustrates that it is possible to disentangle the impact of different external perturbations on the persistence of species. Importantly, our findings show that species interactions may reveal whether communitiesare dominated either by changes in intrinsic growth rates or competition strengths. Overall, this combined framework can open a new perspective to understand and predict the response of populations to changing environmental conditions.

1.Fire activity is changing dramatically across the globe, with uncertain effects on ecosystem processes, especially belowground. Fire‐driven losses of soil carbon (C) are often assumed to occur primarily in the upper soil layers because the repeated combustion of aboveground biomass limits organic matter inputs into surface soil. However, C losses from deeper soil may occur if frequent burning reduces root biomass inputs of C into deep soil layers or stimulates losses of C via leaching and priming.

1.Plant species with broad climatic ranges might be more vulnerable to climate change than previously appreciated due to intraspecific variation in climatic stress tolerance. In tropical forests, drought is increasingly frequent and severe, causing widespread declines and altering community dynamics. Yet, little is known about whether foundation tropical trees vary in drought tolerance throughout their distributions, and how intraspecific variation in drought tolerance might contribute to their vulnerability to climate change.

Increasing temperatures associated with climate change are shifting plant species to higher latitudes. Soil communities could aid the plants’ shift into novel areas by harbouring fewer soil‐borne antagonists or more mutualists that influence the fitness and stress tolerance of the shifting species. Alternatively, they could contain novel antagonists or fewer mutualists. Thus, soil communities could positively or negatively affect plant range expansion, particularly if they influence plants’ responses to climate, such as freeze tolerance, that feedback to affect expansion.

Mutualistic interactions between frugivorous birds and fleshy fruited plants are key processes for both natural plant regeneration and the maintenance of birds relying on fruit resources. However, seed dispersal effectiveness (SDE) has been frequently studied only from the plant's perspective, i.e. the contribution of animals to plant fitness. Using a sample of Atlantic rainforest avian frugivores, this study presents a first comparative, empirical study of fruit effectiveness as a nutritional food resource for seed dispersing birds through the use of Resource‐Provisioning Effectiveness (RPE) models. RPE is the product of the amount of fruits a frugivore can consume (quantity component) and the quality of the ingesta in terms of energy and nutrients obtained (quality component). Our results show wide variation in Resource‐Provisioning Effectiveness among fleshy‐fruited plant species. Energy‐rich fruits consistently show a smaller quantity component, while energetically‐poor fruits are consistently the most consumed, with fruit species spanning a gradient from these two extremes. The specific RPEi resulting from a pairwise fruit‐frugivore interaction is positively correlated to the total RPE (RPET) that a given fruit species has for the whole frugivore assemblage. RPE therefore appears to be a characteristic feature of the fruit species, rather than of the specific frugivore partner. Only the fruit's specific energy content showed a significant phylogenetic signal, suggesting potential constraints for free covariation between RPE and SDE of fruits and frugivores. Synthesis: We analyze variation in the effectiveness of fleshy fruit food provisioning to avian frugivores by explicitly redefining Resource‐Provisioning Effectiveness within the Seed Dispersal Effectiveness framework. We found ample variation in RPE among plant species, showing differences in both quantity and quality components of fruit resources rewards for the frugivores. Our findings help unravel how seed‐dispersing birds may discriminate among alternative fruit resources and to understand the configuration of mutual dependencies among mutualistic partners.

1.Pollinator‐mediated processes (biotic filtering, facilitation or competition) are often inferred by patterns of plant reproductive trait diversity (clustering or evenness of reproductive traits within the community). However, one single pattern can be generated by distinct processes, making difficult to predict the main process of community assembly. Incorporating fitness estimates should improve the link between pattern and process.

1.Understanding how functional traits moderate species’ demographic responses along environmental gradients is a core pursuit in ecology, often to predict how species abundances will respond to a rapidly changing environment. The latter necessitates species demography, or at least abundance, to be modelled directly as a response; yet most studies to‐date use abundance indirectly to calculate and then correlate community‐aggregated trait indices to environmental variables, rendering the prediction of species demographic responses along environmental gradients unfeasible.

1.Biodiversity is considered to mitigate detrimental impacts of climate change on the functioning of forest ecosystems, such as drought‐induced decline in forest productivity. However, previous studies produced controversial results and experimental evidence is rare. Specifically, the biological mechanisms underlying mitigation effects remain unclear, as existing work focuses on biodiversity effects related to the community scale.

1.Increasing temperatures and human activity are likely to reduce fire return intervals in the seasonal tropics. Anticipating how more frequent fires may alter forest community structure and composition requires understanding how fire intensity and species‐specific responses to fires interact to drive fire‐induced mortality for large numbers of species. We developed an analytical framework to estimate unobserved fire intensities and speciesand size‐specific susceptibility to fire using observed mortality data.

1.Community assembly theory assumes that ecological communities are spatially delimited into patches. Within these patches, coexistence results from environmental filtering, competition, and immigration. Truly delineated communities exist in laboratory studies of microbial cultures in Petri dishes, yet empirical tests conducted in continuous environments often use patches defined by convention as opposed to realised boundaries.

In tropical rainforest, most vascular plants have some capacity to resprout, and lianas are often effective resprouters after canopy fall. However, the diversity of resprouting responses of liana species and the consequence for plant persistence is poorly understood. We hypothesized that variation in regeneration among liana species causes differences in liana species abundance in tropical rainforest through differential resprouting capacity, such that liana species with higher densities produce more resprouts after canopy falls.

Trait values affect how plants function, with consequences that propagate through scales of ecological organisation to affect ecosystem function. However, the pathway connecting trait expression to ecosystem function is complicated by feedbacks: trait expression may vary within species in response to community diversity, and trait expression also determines a community's functional diversity. The predictability and consequences of interactions between trait expression and community diversity are poorly understood, particularly in forest ecosystems. Here we quantify the extent to which light access – which past studies suggest affects trait expression and differs as a result of interactions among plants – differs consistently with community diversity and explains intraspecific trait variation in trees. In a common garden, trees of five angiosperm and seven gymnosperm species were planted to form 37 communities ranging widely in species and functional diversity whereby confounding environmental variation was minimised. We sampled leaves of each species to characterise intraspecific variation within and among communities in three traits – leaf size, specific leaf area and nitrogen concentration – and estimated each leaf's access to light. We found that light access explained a substantial portion of trait variation within all species, species tended to receive less light in more diverse communities, and effects of community diversity on trait expression tended to be mediated by light. Synthesis. This study shows that community diversity affects leaf trait plasticity in young trees through its effects on light availability. Moreover, trait responses across angiosperms and gymnosperms were remarkably similar, showing that shared biophysical constraints overwhelm divergent evolutionary histories. Together, these results illustrate how leaf trait expression responds to, and may subsequently shape, diversity in young tree communities in largely predictable ways via resource‐based interactions, with consequences that may scale from individuals to ecosystems.

1.Density‐ and trait‐mediated indirect interactions (DMIIs and TMIIs, respectively) are important drivers of community dynamics but how plant nutrients (bottom‐up effects) affect the magnitude of such indirect interactions has been scarcely addressed.

1.A central challenge of today's ecological research is predicting how ecosystems will develop under future global change. Accurate predictions are complicated by (i) simultaneous effects of different drivers, such as climate change, nitrogen deposition, and management changes; and (ii) legacy effects from previous land use.

1.Information on direct and indirect drivers of temporal variation in ant‐plant interactions is scarce, compromising our ability to predict the functioning of these ecologically important interactions.

1).Decadal changes in masting behaviour—directional changes in seed production with fluctuations on a decadal time scale—are attracting widespread attention in the context of global climate change. However, our mechanistic understanding of the effects of climate on seed production on a decadal scale is unsatisfactory, partly because of insufficient statistical analyses of long‐term data on masting.

The evolution of seed size may be influenced by intrinsic attributes of populations, such as mating system, and extrinsic factors, such as climate. Several hypotheses propose that the evolution of self‐fertilization from an outcrossing progenitor will be accompanied by a reduction in seed size, but this prediction has not been rigorously tested. Many studies report that the mean seed size of populations or taxa is associated with long‐term climate conditions. Here, we examined the effects on seed size of both mating system and climate within a single genus.

1. Negative density dependence (NDD) and niche partitioning have been proposed to explain species coexistence in plant communities. However, the majority of previous studies have examined either only resource partitioning or NDD, or have focused only on a single life history stage. We thus lack knowledge regarding the relative importance of biotic neighborhood interactions and abiotic conditions on survival at the various life stages of a tree.

Where conspecific seedlings occur at high densities, density dependent processes tend to depress their performance and survival relative to co‐occurring heterospecifics. We extend this observation to within‐species genetic diversity and relatedness. We posit that seedling growth and survival increase where there is higher genetic diversity, and lower relatedness, among seedling populations, under the expectation that increased genetic dissimilarity among conspecific seedlings affords greater resistance to pathogens. We used estimates of individual seedling genetic diversity (multilocus heterozygosity (sMLH)) and genetic relatedness among conspecific seedlings (pairwise kinship coefficients (LRI)), under high and low conspecific seedling density, coupled with censuses of seedling growth and mortality over 30 months to explore the role of genetic diversity and relatedness on growth and mortality of 1,485 seedlings of four dipterocarp species in an undisturbed Bornean tropical rain forest. We hypothesized that more genetically diverse and less related co‐occurring seedlings would display higher survival and growth rates. In three of our four species lower genetic diversity increased the probability of mortality over 30 months. We observed no effect of genetic diversity on relative growth rates. Contrary to our expectations only one species showed a negative effect of increased relatedness on mortality. In two of the four species studied, seedlings that were more genetically related to neighbouring conspecific seedlings in the sample plot were less likely to die, but grew more slowly. Synthesis: Our results confirm that genetic diversity and relatedness among seedlings shapes survival probabilities differentially across species. In contrast we found no differences in mortality and growth rates between plots with low and high seedling density. Our results suggest that a greater abundance of pollen donors could contribute to cohort seedling survival in some species, though not all, and the specific mechanisms by which genetic relatedness determines seedling demography remain uncertain. These results have conservation and management implications in view of changing patterns of gene flow in fragmented, exploited, and degraded tropical rain forests, which might differentially influence natural regeneration among species.

Despite the ubiquitous presence of fungal endophytes in woody plants, mechanisms underlying variation in foliar fungal endophyte communities are poorly understood. Given that endophytes in woody plants are predominantly horizontally transmitted, fungal endophyte colonization of foliar tissues is likely to be influenced by plant resistance traits. Here, we evaluated the association between leaf resistance traits and colonization and community composition of horizontally transmitted endophytes (HTE) in 10 dominant trees species in a temperate rainforest in Southern Chile. Because resistance traits might restrict colonization of HTE, it was hypothesized that host trees with similar leaf resistance traits would show similar HTE communities. We measured leaf traits with reported roles in plant resistance against pathogens and/or herbivores: cell wall polysaccharides, leaf toughness, flavonoids, anthocyanins, terpenoids and chitinases. We also determined variation in fungal read counts, number of operational taxonomic units (OTUs), diversity and community structure across tree species. Foliar fungal endophyte communities were characterized using Illumina MiSeq sequencing of tagged amplicons of the ITS1 region. Fungal read counts were significantly different among host trees, while number of OTUs and diversity were similar among them. Multivariate analyses showed that community composition of endophytic fungi significantly differed among hosts, and that variation in cell wall, flavonoids, anthocyanins and terpenoids was associated with differences in HTE communities. We found that host trees sharing leaf resistance traits harbour similar HTE communities. Fungal read counts decreased with increasing content of cell wall polysaccharides, while endophyte diversity decreased with increasing anthocyanin levels. Fungal read counts, in contrast, were positively associated with terpenoids. Additionally, culture‐based data indicated that some HTE strains inhibited the growth of the common fungal pathogen Botrytis cinerea. Synthesis. Overall, we found that leaf resistance traits may influence fungal endophyte colonization and community composition in tree species, likely through deterrent effects of structural and chemical traits. We suggest that endophytic fungi that overcome resistance traits might play a role in plant protection.

Understanding the processes that control alpine treelines, the elevational limits of tree growth forms, has been a central question in ecology and is growing in importance with concern over climate change. Cool summer air temperatures are currently thought to be the ultimate limiter of upright tree growth at alpine treelines globally. However, winter damage has long been recognized as a shaping force near alpine treelines. Low‐growing krummholz growth forms provide an opportunity to test hypotheses about the controls of upright growth in environments above current treelines. To distinguish between effects of growing season temperature, winter damage and their interaction on preventing upright growth in krummholz, we conducted a field experiment on krummholz growth forms of Pinus albicaulis over the summer and winter of 2015–2016 at 10 mountain top sites in the Tobacco Root Mountains, Montana, USA. We experimentally manipulated four factors using a fully crossed design: shoot position (natural low position in the krummholz mat vs. propped up above the krummholz mat), summer warming (warming chamber vs. ambient), winter exposure (shelter cage vs. exposed), and elevation position (local high vs. low krummholz limits). We also conducted an observational study of the climatic conditions associated with recent natural emergent stem establishment from krummholz. Experimentally propped shoots that were exposed in winter experienced the highest mortality (10%–50%), while propped shoots in shelter cages and shoots located within the krummholz mat, whether caged or not, had low mortality (0%–10%). Summer warming had little influence on shoot mortality. Surviving mat shoots had marginally higher growth rates than surviving propped shoots during the early growing season after treatments were established. Natural emergent stem establishment was associated with warmer than average summer temperatures, but also warmer winter temperatures, lower winter wind speeds, and lower snowpack. Synthesis. Our results suggest winter damage plays a more important role than does growing season temperature in maintaining the krummholz growth form. While warming may increase opportunities for emergent shoot establishment above krummholz mats, establishment of upright trees in the krummholz zone will also require climatic change that reduces wind and snow transport which cause winter damage.

1.Trait‐based approaches provide a framework to understand the role of functional biodiversity on ecosystem functioning under global change. While plant traits have been reported as potential drivers of soil microbial community composition and resilience, studies directly assessing microbial traits are scarce, limiting our mechanistic understanding of ecosystem functioning.