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Global change drivers, such as anthropogenic nutrient inputs, are increasing globally. Nutrient deposition simultaneously alters plant biodiversity, species composition and ecosystem processes like aboveground biomass production. These changes are underpinned by species extinction, colonisation and shifting relative abundance. Here, we use the Price equation to quantify and link the contributions of species that are lost, gained or that persist to change in aboveground biomass in 59 experimental grassland sites. Under ambient (control) conditions, compositional and biomass turnover was high, and losses (i.e. local extinctions) were balanced by gains (i.e. colonisation). Under fertilisation, the decline in species richness resulted from increased species loss and decreases in species gained. Biomass increase under fertilisation resulted mostly from species that persist and to a lesser extent from species gained. Drivers of ecological change can interact relatively independently with diversity, composition and ecosystem processes and functions such as aboveground biomass due to the individual contributions of species lost, gained or persisting. EEA Santa Cruz Fil: Ladouceur, Emma. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Ladouceur, Emma. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Ladouceur, Emma. University of Leipzig. Department of Biology; Alemania Fil: Ladouceur, Emma. Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania Fil: Blowes, Shane A. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Blowes, Shane A. Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania Fil: Chase, Jonathan M. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Chase, Jonathan M. Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania Fil: Clark, Adam T. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Clark, Adam T. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Clark, Adam T. Karl-Franzens University of Graz. Institute of Biology; Austria. Fil: Garbowski, Magda. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Garbowski, Magda. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Fil: Alberti, Juan. Universidad Nacional de Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Laboratorio de Ecología. Mar del Plata; Argentina. Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Arnillas, Carlos Alberto. University of Toronto. Department of Physical and Environmental Sciences; Canadá. Fil: Bakker, Jonathan D. University of Washington. School of Environmental and Forest Sciences; Estados Unidos Fil: Barrio, Isabel C. Agricultural University of Iceland. Faculty of Environmental and Forest Sciences; Islandia Fil: Bharath, Siddharth. Atria University; India. Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina. Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Harpole, Stanley. German Centre for Integrative Biodiversity Research (iDiv); Alemania Fil: Harpole, Stanley. Helmholtz Centre for Environmental Research – UFZ. Department of Physiological Diversity; Alemania Martin Luther University Halle-Wittenberg. Institute of Computer Science; Alemania

The effects of altered nutrient supplies and herbivore density on species diversity vary with spatial scale, because coexistence mechanisms are scale dependent. This scale dependence may alter the shape of the species–area relationship (SAR), which can be described by changes in species richness (S) as a power function of the sample area (A): S = cAz, where c and z are constants. We analysed the effects of experimental manipulations of nutrient supply and herbivore density on species richness across a range of scales (0.01–75 m²) at 30 grasslands in 10 countries. We found that nutrient addition reduced the number of species that could co-occur locally, indicated by the SAR intercepts (log c), but did not affect the SAR slopes (z). As a result, proportional species loss due to nutrient enrichment was largely unchanged across sampling scales, whereas total species loss increased over threefold across our range of sampling scales.

Aims Consequences of climate change and land use intensification on the nitrogen (N) cycle of organic-matter rich grassland soils in the alpine region remain poorly understood. We aimed to identify fates of fertilizer N and to determine the overall N balance of an organic-matter rich grassland in the European alpine region as influenced by intensified management and warming. Methods We combined 15N cattle slurry labelling with a space for time climate change experiment, which was based on translocation of intact plant-soil mesocosms down an elevational gradient to induce warming of +1 °C and + 3 °C. Mesocosms were subject to either extensive or intensive management. The fate of slurry-N was traced in the plant-soil system. Results Grassland productivity was very high (8.2 t - 19.4 t dm ha−1 yr−1), recovery of slurry 15N in mowed plant biomass was, however, low (9.6–14.7%), illustrating low fertilizer N use efficiency and high supply of plant available N via mineralization of soil organic matter (SOM). Higher 15N recovery rates (20.2–31.8%) were found in the soil N pool, dominated by recovery in unextractable N. Total 15N recovery was approximately half of the applied tracer, indicating substantial loss to the environment. Overall, high N export by harvest (107–360 kg N ha−1 yr−1) markedly exceeded N inputs, leading to a negative grassland N balance. Conclusions Here provided results suggests a risk of soil N mining in montane grasslands, which increases both under climate change and land use intensification.

Plant community succession is structured by initial richness, plant consumer pressure and soil resource supply. These drivers influence species' trait trade‐offs that underlie temporal changes in plant community diversity. Importantly, how these drivers interact with each other and through time and whether they act on different facets of plant community diversity by promoting different plant trade‐off strategies remains poorly understood. We experimentally manipulated initial plant richness, consumer pressure via pesticide spraying and soil resource supply via fertilization across 4 years of old field succession. We then allowed natural colonization and extinction to occur and examined how the three drivers influenced succession. Specifically, we examined changes in temporal dynamics by conducting yearly taxonomic cover surveys and measuring light penetration to the ground. In the third year, we measured vegetative height and specific leaf area (SLA), and investigated seed mass using a trait database. Higher initial richness, lower consumer pressure and increased soil resource supply all decreased colonizing species richness and light availability and variably altered species evenness. These effects generally acted additively rather than interactively in driving community diversity during succession. However, soil resource supply suppressed consumer pressure effects on species richness and light availability, while consumer pressure and soil resource supply modified initial richness effects on light availability. Treatments acted on different trait identities, revealing different mechanisms underlying taxonomic responses. Initial richness effects on seed mass of colonizing species were modified by soil resource supply. Decreased consumer pressure increased intraspecific community height and decreased interspecific SLA. Increased soil resource supply increased community height, SLA and seed mass. Synthesis. Our results suggest species' resource strategies underlie plant diversity responses to consumer pressure and soil resource supply. Resource addition promoted resource‐acquisitive species; consumer pressure disadvantaged resource‐conservative species. Meanwhile, initial richness altered subsequent community composition primarily through persistence of early residents. We show that community responses to drivers of succession depend on underlying trait trade‐offs of resident species, and these trade‐offs influence community diversity across succession.

Nutrient enrichment can simultaneously increase and destabilise plant biomass production, with co-limitation by multiple nutrients potentially intensifying these effects. Here, we test how factorial additions of nitrogen (N), phosphorus (P) and potassium with essential nutrients (K+) affect the stability (mean/standard deviation) of aboveground biomass in 34 grasslands over 7 years. Destabilisation with fertilisation was prevalent but was driven by single nutrients, not synergistic nutrient interactions. On average, N-based treatments increased mean biomass production by 21-51% but increased its standard deviation by 40-68% and so consistently reduced stability. Adding P increased interannual variability and reduced stability without altering mean biomass, while K+ had no general effects. Declines in stability were largest in the most nutrient-limited grasslands, or where nutrients reduced species richness or intensified species synchrony. We show that nutrients can differentially impact the stability of biomass production, with N and P in particular disproportionately increasing its interannual variability.

Environmental circumstances shaping soil microbial communities have been studied extensively, but due to disparate study designs it has been difficult to resolve whether a globally consistent set of predictors exists, or context-dependency prevails. Here, we used a network of 18 grassland sites (11 sampled across regional plant productivity gradients) to examine i) if the same abiotic or biotic factors predict both large- and regional-scale patterns in bacterial and fungal community composition, and ii) if microbial community composition differs consistently with regional plant productivity (low vs high) across different sites. We found that there is high congruence between predictors of microbial community composition across spatial scales; bacteria were predominantly associated with soil properties and fungi with plant community composition. Moreover, there was a microbial community signal that clearly distinguished high and low productivity soils that was shared across worldwide distributed grasslands suggesting that microbial assemblages vary predictably depending on grassland productivity.

Spatial rarity is often used to predict extinction risk, but rarity can also occur temporally. Perhaps more relevant in the context of global change is whether a species is core to a community (persistent) or transient (intermittently present), with transient species often susceptible to human activities that reduce niche space. Using 5–12 yr of data on 1,447 plant species from 49 grasslands on five continents, we show that local abundance and species persistence under ambient conditions are both effective predictors of local extinction risk following experimental exclusion of grazers or addition of nutrients; persistence was a more powerful predictor than local abundance. While perturbations increased the risk of exclusion for low persistence and abundance species, transient but abundant species were also highly likely to be excluded from a perturbed plot relative to ambient conditions. Moreover, low persistence and low abundance species that were not excluded from perturbed plots tended to have a modest increase in abundance following perturbance. Last, even core species with high abundances had large decreases in persistence and increased losses in perturbed plots, threatening the long-term stability of these grasslands. Our results demonstrate that expanding the concept of rarity to include temporal dynamics, in addition to local abundance, more effectively predicts extinction risk in response to environmental change than either rarity axis predicts alone. © 2021 by the Ecological Society of America

Successful colonization and growth of trees within herbaceous communities may result from different interactions with the herbaceous community. First, colonizing trees compete against larger, established herbs, while subsequent growth occurs among similarly sized or smaller herbs. This shift from colonization to growth may lead three drivers of community dynamics-nutrients, consumers, and herbaceous diversity-to differentially affect tree colonization and, later, tree performance. Initially, these drivers should favor larger, established herbs, reducing tree colonization. Later, when established trees can better compete with herbs, these drivers should benefit trees and increase their performance. In a 4-year study in a southeastern US old field, we added nutrients to, excluded aboveground consumers from, and manipulated initial richness of, the herbaceous community, and then allowed trees to naturally colonize these communities (from intact seedbanks or as seed rain) and grow. Nutrients and consumers had opposing effects on tree colonization and performance: adding nutrients and excluding consumers reduced tree colonization rate, but later increased the size of established trees (height, basal diameter). Adding nutrients and excluding consumers also restricted tree colonization to earlier years of study, which partially explained the effect of nutrient addition on plant size. Together, this shows differing impacts of nutrients and consumers: factors that initially limited tree colonization also resulted in larger established trees. This suggests that succession of grasslands that are either eutrophied or have diminished consumer pressure may experience lags and pulses in woody encroachment, leading to an extended period of herbaceous dominance followed by accelerated woody growth.

Successful alien plant invasion is influenced by both climate change and plant-plant interactions. We estimate the single and interactive effects of competition and extreme weather events on the performance of the global legume invader Lupinus polyphyllus (Lindl.). In three experimental studies we assessed (i) the stress tolerance of seedling and adult L. polyphyllus plants against extreme weather events (drought, fluctuating precipitation, late frost), (ii) the competitive effects of L. polyphyllus on native grassland species and vice versa, and (iii) the interactive effects of extreme weather events and competition on the performance of L. polyphyllus. Drought reduced growth and led to early senescence of L. polyphyllus but did not reduce adult survival. Fluctuating precipitation events and late frost reduced the length of inflorescences. Under control conditions, interspecific competition reduced photosynthetic activity and growth of L. polyphyllus. When subjected to competition during drought, L. polyphyllus conserved water while simultaneously maintaining high assimilation rates, demonstrating increased water use efficiency. Meanwhile, native species had reduced performance under drought. In summary, the invader gained an advantage under drought conditions through a smaller reduction in performance relative to its native competitors but was competitively inferior under control conditions. This provides evidence for a possible invasion window for this species. While regions of high elevation or latitude with regular severe late frost events might remain inaccessible for L. polyphyllus, further spread across Europe seems probable as the predicted increase in drought events may favour this non-native legume over native species.

Correction to: Nature Communications https://doi.org/10.1038/s41467-020-19870-y, published online 27 November 2020.

Droughts can strongly affect grassland productivity and biodiversity, but responses differ widely. Nutrient availability may be a critical factor explaining this variation, but is often ignored in analyses of drought responses. Here, we used a standardized nutrient addition experiment covering 10 European grasslands to test if full-factorial nitrogen, phosphorus, and potassium addition affected plant community responses to inter-annual variation in drought stress and to the extreme summer drought of 2018 in Europe. We found that nutrient addition amplified detrimental drought effects on community aboveground biomass production. Drought effects also differed between functional groups, with a negative effect on graminoid but not forb biomass production. Our results imply that eutrophication in grasslands, which promotes dominance of drought-sensitive graminoids over forbs, amplifies detrimental drought effects. In terms of climate change adaptation, agricultural management would benefit from taking into account differential drought impacts on fertilized versus unfertilized grasslands, which differ in ecosystem services they provide to society.

For succession to proceed from herbaceous to woody dominance, trees must colonize herbaceous communities and grow. Success across these two phases of succession might result from different interactions with the herbaceous community. First, colonizing trees must compete against larger, established herbs, while subsequent growth occurs among similarly sized or smaller herbs. This shift from colonization to growth may cause three drivers of secondary succession— nutrients, consumers, and herbaceous diversity—to differentially affect tree colonization and growth. Initially, these drivers should favor larger, established herbs, reducing colonization. Later, when established trees can better compete with herbs, these drivers should benefit trees and increase their growth. In a four-year study, we added nutrients to, excluded aboveground consumers from, and manipulated initial richness of, the herbaceous community, then allowed trees to naturally colonize these communities (from intact seedbanks or as seed-rain) and grow. Nutrients and consumers had opposing effects on tree colonization and growth: adding nutrients and excluding consumers reduced tree colonization, but later increased established tree growth (height, basal diameter). Together, this shows stage-specific impacts of nutrients and consumers that may improve predictions of the rate and trajectory of succession: factors that initially limited tree colonization later helped established trees to grow.

Eutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale dependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands across the globe and quantify the effect of chronic fertilization on these relationships. Unfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial asynchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities., Eutrophication has been shown to weaken diversity-stability relationships in grasslands, but it is unclear whether the effect depends on scale. Analysing a globally distributed network of grassland sites, the authors show a positive role of beta diversity and spatial asynchrony as drivers of stability but find that nitrogen enrichment weakens the diversity-stability relationships at different spatial scales.

Question Decreased aboveground biomass and subsequent changes in resource availability exert strong influence on seedling recruitment in post-disturbance forests. Ecological tradeoffs underlie recruitment processes, as species vary in resource allocation, dispersal, and stress tolerance strategies. Functional traits that indicate resource acquisition-conservation tradeoffs include leaf nitrogen content, wood density, maximum height, shade tolerance, and drought tolerance, while seed mass can indicate species’ dispersal strategies. This study looks for generality in post-disturbance trait responses, and asks whether these responses are additionally constrained or amplified by disturbance characteristics, climate, and ecological provinces. Location Eastern US temperate forests. Methods I leveraged a longitudinal, continental-scale database of post-disturbance forests to examine recruitment dynamics. Using multivariate, hierarchical Bayesian models, I examined how disturbance affects the traits of seedling layer communities where recruitment dynamics should be most evident, and compared this to undisturbed communities. I also examined how the traits underlying tradeoff axes varied across disturbance properties, ecological provinces, and climatic gradients. Results All traits except for leaf nitrogen showed significant, study-wide shifts in disturbed communities consistent with expectations of post-disturbance stands. In undisturbed plots, all traits had significant shifts in the opposite direction as those observed in disturbed plots, except leaf nitrogen and drought tolerance where no change was observed. Disturbance severity increased the magnitude of response of several, but not all, trait responses in disturbed plots. The traits that had significant shifts were idiosyncratic across ecological provinces, indicating unique processes influencing disturbance responses across the system. Moreover, while climate strongly correlated with all traits prior to disturbance in the initial sampling periods, it was uncorrelated with disturbance responses. Conclusions This study demonstrates general, biome-wide trait shifts towards resource acquisition and bet-hedging dispersal strategies in post-disturbance forest seedling communities. At finer spatial scales, the traits underlying these tradeoffs varied, indicating that disturbance-dependent species differ in life-history strategies across the system. This variation across ecological provinces appears independent of temperature and precipitation, suggesting that unmeasured abiotic or biotic variables influence recruitment. Seedling recruitment is critical in shaping future adult tree communities, and this study reveals large-scale contingencies in trait patterns associated with this process. This article is protected by copyright. All rights reserved.

Higher biodiversity can stabilize the productivity and functioning of grassland communities when subjected to extreme climatic events. The positive biodiversity–stability relationship emerges via increased resistance and/or recovery to these events. However, invader presence might disrupt this diversity–stability relationship by altering biotic interactions. Investigating such disruptions is important given that invasion by non‐native species and extreme climatic events are expected to increase in the future due to anthropogenic pressure. Here we present one of the first multisite invader × biodiversity × drought manipulation experiment to examine combined effects of biodiversity and invasion on drought resistance and recovery at three semi‐natural grassland sites across Europe. The stability of biomass production to an extreme drought manipulation (100% rainfall reduction; BE: 88 days, BG: 85 days, DE: 76 days) was quantified in field mesocosms with a richness gradient of 1, 3, and 6 species and three invasion treatments (no invader, Lupinus polyphyllus, Senecio inaequidens). Our results suggest that biodiversity stabilized community productivity by increasing the ability of native species to recover from extreme drought events. However, invader presence turned the positive and stabilizing effects of diversity on native species recovery into a neutral relationship. This effect was independent of the two invader's own capacity to recover from an extreme drought event. In summary, we found that invader presence may disrupt how native community interactions lead to stability of ecosystems in response to extreme climatic events. Consequently, the interaction of three global change drivers, climate extremes, diversity decline, and invasive species, may exacerbate their effects on ecosystem functioning.

With a growing human population facing multiple global change drivers (i.e. climate change and land management change), the future of food security is of major importance. Sustainable agriculture is therefore key to ensure food supply and food security under future climatic conditions. Forage provision (composed of forage quantity and forage quality) is an important ecosystem service of grasslands for dairy production. However, monitoring forage quality in semi-natural species-rich grasslands is rarely done due to the inherent complexity in determining forage quality, high variability within natural systems and financial and workload restrictions. Here, we i) demonstrate the ability of visible-near-infrared spectroscopy (vis-NIRS) to predict forage quality of bulk samples of species-rich montane pastures and ii) show its potential to reveal effects of two key global change drivers, climate change and land management, on forage quality. Spectral information and chemometrics allowed us to predict three (ash, fat and protein) out of four analyzed forage quality parameters with high accuracy. Land management intensity strongly influenced species-rich grasslands’ protein and fat content, whereas altered climatic conditions influenced ash and fat content. High management intensity increased protein content of high- and mid-elevation pastures by 22 % and 30 % and fat content by 19 % and 20 % respectively. Though forage quality was improved by intensive land management, extensive land management generally revealed sufficient forage quality for livestock. Vis-NIRS provides a rapid, cost-efficient and high-throughput technique to analyze forage quality, revealing effects of global change drivers on forage quality of grasslands. This approach will help to support stakeholders assure optimal nutrition feeding of livestock and achieve steps towards sustainable agriculture.

Human activities are transforming grassland biomass via changing climate, elemental nutrients, and herbivory. Theory predicts that food-limited herbivores will consume any additional biomass stimulated by nutrient inputs (‘consumer-controlled’). Alternatively, nutrient supply is predicted to increase biomass where herbivores alter community composition or are limited by factors other than food (‘resource-controlled’). Using an experiment replicated in 58 grasslands spanning six continents, we show that nutrient addition and vertebrate herbivore exclusion each caused sustained increases in aboveground live biomass over a decade, but consumer control was weak. However, at sites with high vertebrate grazing intensity or domestic livestock, herbivores consumed the additional fertilization-induced biomass, supporting the consumer-controlled prediction. Herbivores most effectively reduced the additional live biomass at sites with low precipitation or high ambient soil nitrogen. Overall, these experimental results suggest that grassland biomass will outstrip wild herbivore control as human activities increase elemental nutrient supply, with widespread consequences for grazing and fire risk., It is unclear whether terrestrial herbivores are able to consume the extra plant biomass produced under nutrient enrichment. Here the authors test this in grasslands using a globally distributed network of coordinated field experiments, finding that wild herbivore control on grassland production declines under eutrophication.

Host and parasite richness are generally positively correlated, but the stability of this relationship in response to global change remains poorly understood. Rapidly changing biotic and abiotic conditions can alter host community assembly, which in turn, can alter parasite transmission. Consequently, if the relationship between host and parasite richness is sensitive to parasite transmission, then changes in host composition under various global change scenarios could strengthen or weaken the relationship between host and parasite richness. To test the hypothesis that host community assembly can alter the relationship between host and parasite richness in response to global change, we experimentally crossed host diversity (biodiversity loss) and resource supply to hosts (eutrophication), then allowed communities to assemble. As previously shown, initial host diversity and resource supply determined the trajectory of host community assembly, altering post-assembly host species richness, richness-independent host phylogenetic diversity, and colonization by exotic host species. Overall, host richness predicted parasite richness, and as predicted, this effect was moderated by exotic abundance-communities dominated by exotic species exhibited a stronger positive relationship between post-assembly host and parasite richness. Ultimately, these results suggest that, by modulating parasite transmission, community assembly can modify the relationship between host and parasite richness. These results thus provide a novel mechanism to explain how global environmental change can generate contingencies in a fundamental ecological relationship-the positive relationship between host and parasite richness.

Host and parasite richness are generally positively correlated, but the stability of this relationship during community assembly remains untested. The composition of host communities can alter parasite transmission, and the relationship between host and parasite richness is sensitive to parasite transmission. Thus, changes in composition during host community assembly could strengthen or weaken the relationship between host and parasite richness. Host community assembly, in turn, can be driven by many processes, including resource enrichment. To test the hypothesis that host community assembly can alter the relationship between host and parasite richness, we experimentally crossed host diversity and resource supply to hosts, then allowed communities to assemble. As previously shown, initial host diversity and resource supply determined the trajectory of host community assembly, altering post-assembly host species richness, richness-independent host phylogenetic diversity, and colonization by exotic host species. Throughout community assembly, host richness predicted parasite richness. As predicted, this effect was moderated by exotic abundance: communities dominated by exotic species exhibited a stronger positive relationship between post-assembly host and parasite richness. Ultimately, these results suggest that, by modulating parasite transmission, community assembly can modify the relationship between host and parasite richness, providing a novel mechanism to explain contingencies in this relationship.

A Correction to this paper has been published: https://doi.org/10.1038/s41467-021-20997-9.

1. Climate change is a world-wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil–plant–atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high-quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re-use, synthesis and upscaling. Many of these challenges relate to a lack of an established ‘best practice’ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. 2. To overcome these challenges, we collected best-practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re-use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re-use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second-order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's best practice, coordinated experiments, data management and documentation, ecosystem, experimental macroecology, methodology, open science, vegetation This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2019 The Authors. Methods in Ecology and Evolution published by John Wiley & Sons Ltd on behalf of British Ecological Society.

Infectious disease risk is often influenced by host diversity, but the causes are unresolved. Changes in diversity are associated with changes in community structure, particularly during community assembly; therefore, by incorporating change over time, host community assembly may provide a framework to resolve causation. In turn, community assembly can be driven by many processes, including resource enrichment. To test the hypothesis that community assembly causally links host diversity to future disease, we experimentally manipulated host diversity and resource supply to hosts, then allowed communities to assemble for 2 years (surveyed 2012-2014). Initially, host diversity increased disease. Subsequently, host diversity did not directly alter disease. However, host diversity determined the trajectory of host community assembly, altering colonisation by exotic host species and richness-independent host phylogenetic diversity, which together reversed the initial increase in disease. Ultimately, incorporating the temporal dimension of community assembly revealed novel mechanisms linking host diversity to future disease.

Throughout the eastern deciduous forest (EDF) region, disturbances, including fire, wind storms, and landslides, interweave with complex topography and vegetation history to produce a mosaic of forest types and ages. Forest composition and dynamics following disturbance can depend on the interaction of plant traits related to resource capture, regeneration, and growth with changes in the post-disturbance environment. Appropriate traits should vary predictably with the stand age of a forest community as this acts as a proxy for time since last disturbance. We used Forest Inventory and Analysis data to investigate the hypothesis that community level means of seed mass and wood density increase, and leaf nitrogen decreases, with age of eastern deciduous forests, reflecting a shift from light-seeded, fast-growing early successional vegetation to heavier-seeded, slower-growing vegetation. As hypothesized, seed mass and wood density were positively correlated with stand age; however, the relationship differed among ecoregions of the EDF. Northern forests in the Warm Continental Division showed lower seed mass and wood density values in young stands, with a stronger increase in these values as succession advanced relative to more southerly ecoregions. This could reflect slower succession, preponderance of light-seeded and low wood density early post-disturbance deciduous trees such as Populus tremuloides and Betula papyrifera, or presence of conifers in early successional stands. Leaf nitrogen showed no consistent relationship with stand age, suggesting no consistent relationship of photosynthetic rate or soil nitrogen content with tree composition over succession throughout the EDF. Instead, leaf nitrogen differed among the ecoregion divisions and showed a unimodal distribution with latitude, peaking near the middle latitudes of the Hot Continental and Prairie Divisions. Collectively, the results indicate functional trait shifts over succession throughout the EDF, in agreement with a shift from ruderal to more competitive or stress-tolerant strategies, but also point to differences in the strength and shape of that shift among ecoregions. Early post-disturbance forest harbors a unique combination of functional traits. Further, disturbance that creates a mosaic of forest stand ages is important for maximizing not just species diversity, but functional diversity as well.

The stress-dominance hypothesis (SDH) is a model of community assembly predicting that the relative importance of environmental filtering increases and competition decreases along a gradient of increasing environmental stress. Tests of the SDH at limited spatial scales have thus far demonstrated equivocal support and no prior study has assessed the generality of the SDH at continental scales. We examined over 53 000 tree communities spanning the eastern United States to determine whether functional trait variation and phylogenetic diversity support the SDH for gradients of water and soil nutrient availability. This analysis incorporated two complementary datasets, those of the U.S. Forest Service Forest Inventory and Analysis National program and the Carolina Vegetation Survey, and was based on three ecologically important traits: leaf nitrogen, seed mass, and wood density. We found that mean trait values were weakly correlated with water and soil nutrient availability, but that trait diversity did not vary consistently along either gradient. This did not conform to trait variation expected under the SDH and instead suggested that environmental filters structure tree communities throughout both gradients, without evidence for an increased role of competition in less stressful environments. Phylogenetic diversity of communities was principally driven by the ratio of angiosperms to gymnosperms and therefore did not exhibit the pattern of variation along stress gradients expected under the SDH. We conclude that the SDH is not a general paradigm for all eastern North American tree communities, although it may operate in certain contexts.

Many factors can promote exotic plant success. Three of these factors-greater pressure from natural enemies on natives, increased soil nutrient supply, and low native species richness-may interact during invasions. To test for independent and interactive effects of these drivers, we planted herbaceous perennial communities at two levels of native richness (monocultures and five-species polycultures). We then factorially manipulated soil nutrient supply and access to these communities by aboveground foliar enemies (fungal pathogens and insect herbivores), and allowed natural colonization to proceed for four years. We predicted that nutrient addition would increase exotic success, while enemy exclusion and increasing native richness would reduce exotic success. Additionally, we expected that enemy exclusion would reduce the benefits of nutrient addition to exotic species most in species-poor communities, and that this effect would be weaker in species-rich communities. In total, we found no evidence that nutrient supply, enemy access, and native richness interacted to influence exotic success. Furthermore, native richness had no effect on exotic success. Instead, nutrient addition increased, and enemy exclusion decreased, exotic success independently. As predicted, enemy exclusion reduced exotic success, primarily by slowing the decline in abundance of planted native species. Together, these results demonstrate that multiple drivers of exotic success can act independently within a single system.

Community theory proposes that the taxonomic diversity and characteristics, or traits, of the trees found within a particular forest community is a function of both the productivity and disturbance history of that community. The theory also predicts that niche differentiation to the conditions caused by disturbance is strongest on productive sites and decreases along productivity gradients. Therefore, both taxonomic and trait diversity should be highest on productive sites at scales that encompass a range of disturbance histories, and lowest on poor quality sites where environmental conditions are strong ‘filters’ for plant traits. Using a large data set from the USDA Forest Service, we examine patterns of taxonomic and tree trait diversity with respect to recent disturbance events and productivity across the Central Hardwood Region. Our analyses reveal strong regional trends in diversity, less pronounced trends along the productivity gradient, and little effect of disturbance on tree diversity and characteristics.

Theory predicts that increasing biodiversity will dilute the risk of infectious diseases under certain conditions and will amplify disease risk under others. Yet, few empirical studies demonstrate amplification. This contrast may occur because few studies have considered the multivariate nature of disease risk, which includes richness and abundance of parasites with different transmission modes. By combining a multivariate statistical model developed for biodiversity–ecosystem–multifunctionality with an extensive field manipulation of host (plant) richness, composition and resource supply to hosts, we reveal that (i) host richness alone could not explain most changes in disease risk, and (ii) shifting host composition allowed disease amplification, depending on parasite transmission mode. Specifically, as predicted from theory, the effect of host diversity on parasite abundance differed for microbes (more density-dependent transmission) and insects (more frequency-dependent transmission). Host diversity did not influence microbial parasite abundance, but nearly doubled insect parasite abundance, and this amplification effect was attributable to variation in host composition. Parasite richness was reduced by resource addition, but only in species-rich host communities. Overall, this study demonstrates that multiple drivers, related to both host community and parasite characteristics, can influence disease risk. Furthermore, it provides a framework for evaluating multivariate disease risk in other systems.