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Soil bacterial and fungal communities play fundamental roles in biogeochemical cycles and ecosystem stability. Urbanization alters soil properties and microbial habitats, driving shifts in community composition, yet the divergent responses of bacteria and fungi and their ecological consequences remain inadequately understood. To elucidate these differential responses, we investigated soil bacterial and fungal communities along an urbanization gradient, ranging from undisturbed reference forests to urban parks, across three distinct climatic regions. To capture different disturbance intensities, urban parks were classified by tree age into old parks (>60-year-old trees) and young parks (10–20-year-old trees). Climate had a strong influence on soil microbiota, yet urbanization still significantly altered both bacterial and fungal communities in all regions. Urban disturbances homogenized soil microbial communities: average similarity among bacterial communities increased from ∼79 % in forests to ∼85 % in young urban parks, indicating substantial homogenization, whereas fungal communities showed little homogenization. Urbanization also homogenized microbial functional traits, with a greater reduction in trait dissimilarity for bacteria than for fungi. Bacterial communities exhibited high adjustability to urban conditions, dominated by generalist taxa (∼90 %), whereas fungal communities consisted mostly of specialists (∼83 %). Despite these asynchronous responses—bacteria adjusting and homogenizing more than fungi—overlapping functional traits between bacteria and fungi help maintain functional resilience in urban ecosystems.

Changes in fire regime of boreal forests in response to climate warming are expected to impact postfire recovery. However, quantitative data on how managed forests sustain and recover from recent fire disturbance are limited. Two years after a large wildfire in managed even‐aged boreal forests in Sweden, we investigated how recovery of aboveground and belowground communities, that is, understory vegetation and soil microbial and faunal communities, responded to variation in the severity of soil (i.e., consumption of soil organic matter) and canopy fires (i.e., tree mortality). While fire overall enhanced diversity of understory vegetation through colonization of fire adapted plant species, it reduced the abundance and diversity of soil biota. We observed contrasting effects of tree‐ and soil‐related fire severity on survival and recovery of understory vegetation and soil biological communities. Severe fires that killed overstory Pinus sylvestris promoted a successional stage dominated by the mosses Ceratodon purpureus and Polytrichum juniperinum , but reduced regeneration of tree seedlings and disfavored the ericaceous dwarf‐shrub Vaccinium vitis‐idaea and the grass Deschampsia flexuosa . Moreover, high tree mortality from fire reduced fungal biomass and changed fungal community composition, in particular that of ectomycorrhizal fungi, and reduced the fungivorous soil Oribatida. In contrast, soil‐related fire severity had little impact on vegetation composition, fungal communities, and soil animals. Bacterial communities responded to both tree‐ and soil‐related fire severity. Synthesis : Our results 2 years postfire suggest that a change in fire regime from a historically low‐severity ground fire regime, with fires that mainly burns into the soil organic layer, to a stand‐replacing fire regime with a high degree of tree mortality, as may be expected with climate change, is likely to impact the short‐term recovery of stand structure and above‐ and belowground species composition of even‐aged P. sylvestris boreal forests.

Foundation species provide habitat and modify the availability of resources to other species. In nature, multiple foundation species may occur in mixture, but little is known on how their interactions shape the community assembly of associated species. Lichens provide both structural habitat and resources to a variety of associated organisms and thereby serve as foundation species. In this study, we use mat-forming lichens and their associated micro-arthropods as a miniature ecosystem to study potential synergies between foundation species diversity and the abundance and functional diversity of higher trophic levels. We created lichen patches with monocultures and mixtures of up to four species, and extracted Collembola (identified to species level), Oribatida, Mesostigmata, Pseudoscorpiones, and Araneae with Tullgren apparatuses after 106 days of incubation within a natural lichen mat. We found that different lichen species supported different arthropod abundances. For 19 out of a total of 55 lichen mixtures and arthropod groups, we found non-additive, synergistic effects on arthropod abundance, although the specific lichen mixture causing synergistic effects differed with arthropod group. In addition, synergistic effects on arthropod abundance were more common for arthropod groups at lower trophic levels. The functional diversity of lichen mixtures explained patterns in Collembola abundance, but in the opposite direction than hypothesized because synergistic responses were more frequent in functionally similar lichen mixtures. Finally, we found few effects of lichen mixture identity or diversity on the functional diversity of Collembola communities. When applied to large-scale ecosystems, our results suggest that understanding interactions between coexisting foundation species and identifying those species that drive synergistic effects of foundation species on consumer biota, is likely to be of importance to biodiversity conservation and restoration efforts.

Summary Plant–soil feedbacks is becoming an important concept for explaining vegetation dynamics, the invasiveness of introduced exotic species in new habitats and how terrestrial ecosystems respond to global land use and climate change. Using a new conceptual model, we show how critical alterations in plant–soil feedback interactions can change the assemblage of plant communities. We highlight recent advances, define terms and identify future challenges in this area of research and discuss how variations in strengths and directions of plant–soil feedbacks can explain succession, invasion, response to climate warming and diversity‐productivity relationships. While there has been a rapid increase in understanding the biological, chemical and physical mechanisms and their interdependencies underlying plant–soil feedback interactions, further progress is to be expected from applying new experimental techniques and technologies, linking empirical studies to modelling and field‐based studies that can include plant–soil feedback interactions on longer time scales that also include long‐term processes such as litter decomposition and mineralization. Significant progress has also been made in analysing consequences of plant–soil feedbacks for biodiversity‐functioning relationships, plant fitness and selection. To further integrate plant–soil feedbacks into ecological theory, it will be important to determine where and how observed patterns may be generalized, and how they may influence evolution. Synthesis . Gaining a greater understanding of plant–soil feedbacks and underlying mechanisms is improving our ability to predict consequences of these interactions for plant community composition and productivity under a variety of conditions. Future research will enable better prediction and mitigation of the consequences of human‐induced global changes, improve efforts of restoration and conservation and promote sustainable provision of ecosystem services in a rapidly changing world.

Global warming is changing plant communities due to the arrival of new species from warmer regions and declining abundance of cold‐adapted species. However, experimentally testing predictions about trajectories and rates of community change is challenging because we normally lack an expectation for future community composition, and most warming experiments fail to incorporate colonization by novel species. To address these issues, we analyzed data from 44 whole‐community transplant experiments along 22 elevational gradients across the Northern Hemisphere. In these experiments, high‐elevation communities were transplanted to lower elevations to simulate warming, while also removing dispersal barriers for lower‐elevation species to establish. We quantified the extent and pace at which warmed high‐elevation communities shifted towards the taxonomic composition of lower elevation communities. High‐elevation plant communities converged towards the composition of low‐elevation communities, with higher rates under stronger experimental warming. Strong community shifts occurred in the first year after transplantation then slowed over time, such that communities remained distinct from both origin and destination control by the end of the experimental periods (3‐9 years). Changes were driven to a similar extent by both new species colonization and abundance shifts of high‐elevation species, but with substantial variation across experiments that could be partly explained by the magnitude and duration of experimental warming, plot size and functional traits. Our macroecological approach reveals that while warmed high‐elevation communities increasingly resemble communities at lower elevations today, the slow pace of taxonomic shifts implies considerable colonization and extinction lags, where a novel taxonomic composition of both low‐ and high‐elevation species could coexist for long periods of time. The important contribution of the colonizing species to community change also indicates that once dispersal barriers are overcome, warmed high‐elevation communities are vulnerable to encroachment from lower elevation species.

Decomposition and fire are major carbon pathways in many ecosystems, yet the contribution of species identity to these processes can be difficult to predict. Plant decomposability and flammability have usually been studied separately but could be linked through shared predictive traits. We explored how decomposability and flammability were related to each other and to key plant functional traits in a tropical swamp forest in Singapore. Full methodological details <em>in situ</em> decomposition experiment in Nee Soon freshwater swamp forest, Singapore, laboratory flammability experiment, and leaf functional trait measurements can be found in the published article and supporting information stated below. Nur E. B. Rahman, Stuart W. Smith, Weng Ngai Lam, Kwek Yan Chong, Matthias S. E. Chua, Pei Yun Teo, Daniel W. J. Lee, Shi Yu Phua, Cheryl Y. Aw, Janice S. H. Lee, David A. Wardle. Leaf decomposition and flammability are largely decoupled across species in a tropical swamp forest despite sharing some predictive leaf functional traits. <em>New Phytologist</em> In this data repository, we have uploaded the following decomposition, flammability and trait data as well as secondary data used in our statistical analyses to generate the findings presented in the paper. Specific datasets include the following: litter_mass_loss.csv : raw data of leaf litterbag dry masses before and after 1 year in situ decomposition experiment in Nee Soon Swamp Forest flammability_leaf_temperature.csv : raw data of temperature recorded during flammability experiments of leaf litter and fresh leaves flammability_timings.csv : raw data of timings of flammability events, namely smouldering and pyrolysis recorded from video footage of flammability experiments senesced_leaf_dryweights_area.csv : senesced leaf raw data for calculating physical traits senesced_leaf_dryweights.csv: senesced leaf dry weights raw data freshtraits_measurements.csv: fresh leaf raw data for calculating physical traits decomposition_constants.csv: derived decomposition constants (k) for each species from the analysis of decomposition experiments. functional_traits_z_standardized.csv : all traits required for the analysis, consolidated following z-standardized transformation functional_traits_untransformed_decomposition_flammability.csv : all traits required for the analysis, untransformed (for back transforming axis labels) and species decomposition and flammability variables Raw leaf litter mass loss and leaf flammability data are associated meta-data file explaining the column headers and variables. For all other datasets please refer to the paper and supporting information.

Ongoing Arctic greening can increase productivity and reindeer pasture quality in the tundra. However, greening may also entail proliferation of unpalatable species, with distinct consequences for pastoral socio-ecological systems (SES). We show extensive greening across 20 reindeer districts in northern Norway between 2003 and 2020. The allelopathic, evergreen dwarf-shrub crowberry biomass increased by 60%, contrasted by smaller increases of deciduous dwarf-shrubs and stagnating forb and graminoid biomass. We found evidence, although uncertain, of a negative relationship between biomass and reindeer densities, but only among forbs, the least abundant plant group. Our results challenge the management decision-making, which aims at sustainable pasture management, but which assumes stationary density-dependent relationships. Changes in temporal vs. spatial relationships should be included as management criteria, to avoid mismanaging a SES in transition. Large-scale shift towards increased allelopathy may undermine the resource base of a key Arctic herbivore and pastoral SES.

There is growing recognition of the need to incorporate intraspecific trait variability (ITV) into trait‐based studies to improve understanding of community assembly and how plant communities drive ecosystem processes. However, most studies have focused on ITV across plant communities, with few quantifying it at local scales. Further, little is known about how ITV at local scales differs among communities or across environmental gradients. Here, we studied a well characterized 5000‐year‐old chronosequence involving 30 islands that differed greatly in size, soil fertility, spatial heterogeneity, and species diversity. On each island we measured foliar and litter (including nutrient resorption) traits for ten individuals for each of three species that occur on all islands, i.e., Betula pubescens , Vaccinum myrtillus and Vaccinium vitis‐idaea . For each trait for each species we estimated its within‐island mean, and coefficient of variation as a measure of local scale ITV. We predicted within‐island ITV should be highest for larger islands that have the greatest spatial heterogeneity of soil resources but lowest species diversity. Further, we predicted that the species most dominant in the most resource heterogeneous environment ( V. myrtillus ) should have the greatest within‐island ITV. First, we found that within‐island ITV of foliar traits was generally unresponsive to island size, while for litter traits it was responsive to island size only for V. myrtillus in a direction consistent with our prediction. The within‐island ITV of resorption efficiency of C, N and P for the three species was often responsive to island size, but not in a consistent direction. Second, against our prediction, V. myrtillus had the lowest within‐island ITV for most traits, but its within‐island ITV was generally more responsive than that of the other species to island size. While plant traits are well known to vary among and within species at broad spatial scales across environmental gradients, our results show that at local scales, ITV can also be highly responsive to fine scale environmental gradients, particularly for litter and nutrient resorptive traits. Understanding how local scale ITV varies across communities offers opportunities for improving our understanding of what drives community assembly, functional diversity and ecosystem processes.

Summary 1. Many ecosystems are gaining some species and losing others, leading to large shifts in community composition. Plants that support nitrogen ( N )‐fixing symbionts (hereafter N ‐fixers) are major ecosystem drivers but human‐induced environmental changes can lead to their loss; the impacts of this loss have seldom been studied. In N ew Z ealand, the gain of some invasive herbivorous mammals leads to the loss of N ‐fixing shrubs that are pioneers during primary succession. 2 . We studied primary successional surfaces caused by river floods and landslides in a remote valley in N ew Z ealand's S outh I sland. We set up and maintained a removal experiment over 10 years, with N ‐fixing C armichaelia odorata (hereafter C armichaelia ) either left intact or removed to represent the effects that invasive herbivorous mammals could cause under high densities. 3 . Above‐ground effects of 10 years of C armichaelia removal included a 7‐fold reduction of woody plant biomass, but had no effect on the shorter non‐woody vegetation. Foliar N concentrations of two woody species were also reduced. C armichaelia removal reduced local or α‐diversity but enhanced β‐diversity of the remaining vegetation at the functional group but not the species level. 4. Below‐ground effects of 10 years of C armichaelia removal included large reductions in soil carbon ( C ) and N levels, and biomass or abundance of several groups of soil biota occupying three consumer trophic levels as well as the root‐, bacterial‐ and fungal‐based energy channels. Invertebrate bacterial consumers were more adversely affected than were fungal consumers. C armichaelia loss reduced α‐diversity of some below‐ground groups, while β‐diversity was unresponsive or enhanced. 5 . Synthesis . Our results reveal that loss of a single functionally distinct plant species, such as occurs through herbivore invasion, can cause substantial effects both above‐ground and below‐ground. This may affect the trajectory of the ecosystem over successional time, especially in primary seres that otherwise have very low soil carbon ( C ) and nitrogen ( N ) reservoirs. More generally, our results support the view that the simultaneous gains of some organisms (e.g. invasive herbivorous mammals) and resultant losses of others (e.g. palatable N ‐fixing plants) are a major element of human‐induced global change that may be transforming many communities and ecosystems world‐wide.

Despite a major research focus on human‐mediated reshuffling of plant communities, no coherent framework unites the numerous types of changes in abundances and distributions of native and non‐native species that are driven by human activities. Human driven vegetation change can occur through: non‐native species introductions; population outbreaks or collapses; range expansions or contractions; and range shifts of both native and non‐native species. Boundaries among these different types of floristic changes are not always distinct because of an overlap in the ecological, climatic, and anthropogenic processes that underpin them. We propose a new framework that connects various human‐mediated causes of vegetation change, highlights the spatial scales at which drivers act and the temporal scale at which plant assemblages respond, and provides critical insights for identifying and appropriately managing these changes.