Species turnover is ubiquitous. However, it remains unknown whether certain types of species are consistently gained or lost across different habitats. Here, we analysed the trajectories of 1827 plant species over time intervals of up to 78 years at 141 sites across mountain summits, forests, and lowland grasslands in Europe. We found, albeit with relatively small effect sizes, displacements of smaller- by larger-ranged species across habitats. Communities shifted in parallel towards more nutrient-demanding species, with species from nutrient-rich habitats having larger ranges. Because these species are typically strong competitors, declines of smaller-ranged species could reflect not only abiotic drivers of global change, but also biotic pressure from increased competition. The ubiquitous component of turnover based on species range size we found here may partially reconcile findings of no net loss in local diversity with global species loss, and link community-scale turnover to macroecological processes such as biotic homogenisation. 

• Forests harbour large spatiotemporal heterogeneity in canopy structure. This variation drives the microclimate and light availability at the forest floor. So far, we do not know how light availability and sub-canopy temperature interactively mediate the impact of macroclimate warming on understorey communities.
• We therefore assessed the functional response of understorey plant communities to warming and light addition in a full factorial experiment installed in temperate deciduous forests across Europe along natural microclimate, light and macroclimate gradients. Furthermore, we related these functional responses to the species’ life-history syndromes and thermal niches.
• We found no significant community responses to the warming treatment. The light treatment, however, had a stronger impact on communities, mainly due to responses by fast-colonizing generalists and not by slow-colonizing forest specialists. The forest structure strongly mediated the response to light addition and also had a clear impact on functional traits and total plant cover.
• The effects of short-term experimental warming were small and suggest a time-lag in the response of understorey species to climate change. Canopy disturbance, for instance due to drought, pests or logging, has a strong and immediate impact and particularly favours generalists in the understorey in structurally complex forests.

1. In many agricultural landscapes, it is important to restore networks of forests to provide habitat and stepping stones for forest specialist taxa. More knowledge is, however, needed on how to facilitate the immigration of such taxa in restored forest patches. Here, we present the first chronosequence study to quantify the dynamics of immigration credits of forest specialist plants in post-arable forest patches.
2. We studied the distribution of herbaceous forest specialist plant species in 54 post-arable broadleaved forest patches along gradients of age (20–140 years since forest establishment), distance from ancient forest (0–2,600 m) and patch area (0.5–9.6 ha). With linear mixed models, we estimated the effects of these factors on species richness, patch means of four dispersal-related plant traits and with generalized linear models on the occurrence of 20 individual species.
3. Post-arable forest patch age and spatial isolation from ancient forest, but not patch size, were important predictors for species richness of forest specialists, suggesting that also small patches are valuable for habitat connectivity. Compared to species richness in ancient forest stands, the immigration credit was reduced by more than 90% after 80 years in post-arable forest patches contiguous to ancient forest compared to 40% after 80 years and 60% after 140 years in isolated patches (at least 100 m to next forest). Tall-growing species with adaptations to long-distance dispersal were faster colonizers, whereas species with heavy diaspores and clonal growth were slower to colonize.
4. Synthesis and applications. We show that post-arable oak plantations have a high potential for restoration of forest herb vegetation. Dispersal-related plant traits play a key role in explaining interspecific differences among forest specialists. To facilitate forest herb immigration across all functional groups in agricultural landscapes, we suggest to create clusters of relatively small new forest patches nearby older forest with source populations.

Aim: The spatio-temporal connectivity of forest patches in lowland agricultural landscapes and their age matter to explain current biodiversity patterns across regional as well as biogeographical extents, to the point that their effect exceeds the one of macroclimate for plant diversity in the understorey of temperate forests. Whether this remains true for other taxonomic groups is still largely unknown. Yet, this relative influence has important consequences for ecosystem functioning and the delivery of ecosystem services. Focusing on carabid beetle assemblages, we assessed the relative importance of macroclimatic, landscape and patch attributes in driving local species richness (alpha-diversity) and species dissimilarity between patches (beta-diversity).

Location: Deciduous forest patches in seven regions along a 2,100-km-long latitudinal gradient across the European temperate forest biome, from southern France to central Sweden.

Methods: We sampled 221 forest patches in two 5-km x 5-km landscape windows with contrasting management intensities. Carabid beetles were classified into four habitat-preference guilds: forest-specialist, forest-generalist, eurytopic and open-habitat species. We quantified the multi-level environmental influence using mixed-effects models and variation partitioning analysis.

Results: We found that both alpha- and beta-diversity were primarily determined by macroclimate, acting as a large-scale ecological filter on carabid assemblages among regions. Forest-patch conditions, including biotic and abiotic heterogeneity as well as patch age (but not patch size), increased alpha-diversity of forest species. Landscape management intensity weakly influenced alpha-diversity of forest species, but increased the number of non-forest species in forest patches. Beta diversity of non-forest species increased with patch heterogeneity and decreased with landscape management intensity.

Main conclusions: Our results highlight the leading role of broad macroclimatic gradients over local and landscape factors in determining the composition of local carabid communities, thereby shedding light on macroecological patterns of arthropod assemblages. This study emphasizes the urgent need for preserving ancient forest patches embedded in agricultural landscapes, even the small and weakly connected ones.

Questions: Does the influence of forest edges on plant species richness and composition depend on forest management? Do forest specialists and generalists show contrasting patterns?

Location: Mesic, deciduous forests across Europe.

Methods: Vegetation surveys were performed in forests with three management types (unthinned, thinned 5-10 years ago and recently thinned) along a macroclimatic gradient from Italy to Norway. In each of 45 forests, we established five vegetation plots along a south-facing edge-to-interior gradient (n = 225). Forest specialist, generalist and total species richness, as well as evenness and proportion of specialists, were tested as a function of the management type and distance to the edge while accounting for several environmental variables (e.g. landscape composition and soil characteristics). Magnitude and distance of edge influence were estimated for species richness per management type.

Results: Greatest total species richness was found in thinned forests. Edge influence on generalist plant species richness was contingent on the management type, with the smallest decrease in species richness from the edge-to-interior in unthinned forests. In addition, generalist richness increased with the proportion of forests in the surrounding landscape and decreased in forests dominated by tree species that cast more shade. Forest specialist species richness, however, was not affected by management type or distance to the edge, and only increased with pH and increasing proportion of forests in the landscape.

Conclusions: Forest thinning affects the plant community composition along edge-to-interior transects of European forests, with richness of forest specialists and generalists responding differently. Therefore, future studies should take the forest management into account when interpreting edge-to-interior because both modify the microclimate, soil processes and deposition of polluting aerosols. This interaction is key to predict the effects of global change on forest plants in landscapes characterized by the mosaic of forest patches and agricultural land that is typical for Europe.

Linear landscape elements such as hedgerows and road verges have the potential to mitigate the adverse effects of habitat fragmentation and climate change on species, for instance, by serving as a refuge habitat or by improving functional connectivity across the landscape. However, so far this hypothesis has not been evaluated at large spatial scales, preventing us from making generalized conclusions about their efficacy and implementation in conservation policies. Here, we assessed plant diversity patterns in 336 vegetation plots distributed along hedgerows and road verges, spanning a macro-environmental gradient across temperate Europe. We compared herb-layer species richness and composition in these linear elements with the respective seed-source (core) habitats, that is, semi-natural forests and grasslands. Next, we assessed how these differences related to several environmental drivers acting either locally, at the landscape level or along the studied macro-ecological gradient. Across all regions, about 55% of the plant species were shared between forests and hedgerows, and 52% between grasslands and road verges. Habitat-specialist richness was 11% lower in the linear habitats than in the core habitats, while generalist richness was 14% higher. The difference in floristic composition between both habitat types was mainly due to species turnover, and not nestedness. Most notably, forest-specialist richness in hedgerows responded positively to tree cover, tree height and the proportion of forests in the surrounding landscape, while generalist richness was negatively affected by tree height and buffering effect of trees on subcanopy temperatures. Grassland and road verge diversity was mainly influenced by soil properties, with positive effects of basic cation levels on the number of specialists and those of bioavailable soil phosphorus on generalist diversity. Synthesis and applications. We demonstrate that linear landscape elements provide a potential habitat for plant species across Europe, including slow-colonizing specialists. Additionally, our results stress the possibility for land managers to modify local habitat features (e.g. canopy structure, subcanopy microclimate, soil properties, mowing regime) through management practices to enhance the colonization success of specialists in these linear habitats. These findings underpin the management needed to better conserving the biodiversity of agricultural landscapes across broad geographical scales.