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1 Disturbance may cause community composition across sites to become more or less homogenous, depending on the importance of different processes involved in community assembly. In north-eastern North America and Europe local (alpha) diversity of forest plants is lower in forests growing on former agricultural fields (recent forests) than in older (ancient) forests, but little is known about the influence of land-use history on the degree of compositional differentiation among sites (beta diversity). 2 Here we analyse data from 1446 sites in ancient and recent forests across 11 different landscapes in north-eastern North America and Europe to demonstrate decreases in beta diversity and in the strength of species-environment relationships in recent vs. ancient forests. 3 The magnitude of environmental variability among sites did not differ between the two forest types. This suggests the difference in beta diversity between ancient and recent forests was not due to different degrees of environmental heterogeneity, but rather to dispersal filters that constrain the pool of species initially colonizing recent forests. 4 The observed effects of community homogenization and weakened relationships between species distributions and environmental gradients appear to persist for decades or longer. The legacy of human land-use history in spatial patterns of biodiversity may endure, both within individual sites and across sites, for decades if not centuries.

Anthropogenic activities have affected forests for centuries, leading to persistent legacies. Observations of agricultural legacies on forest soil properties have been site specific and contrasting. Sites and regions vary along gradients in intrinsic soil characteristics, phosphorus (P) management and nitrogen (N) deposition which could affect the magnitude of soil property responses to past cultivation. A single investigation along these gradients could reconcile contradictions and elucidate context-dependency in agricultural legacies. We analysed soil from 24 paired post-agricultural (established after approx. 1950) and ancient (in existence before 1850) forests in eight European regions. Post-agricultural forest soil had higher pH, higher P-concentration and lower carbon (C) to N ratio compared to ancient forest. Importantly, gradients of soil characteristics, regional P surplus and N deposition affected the magnitude of these legacies. First, we found that three soil groups, characterising inherent soil fertility, determined extractable base cations, pH and concentrations of total N, organic C and total P. Second, regions with greater current P surplus from agriculture correlated with the highest P legacy in post-agricultural forests. Finally, we found that N deposition lowered pH across forests and increased total N and organic C concentrations in post-agricultural forest. These results suggest that (1) legacies from cultivation consistently determine soil properties in post-agricultural forest and (2) these legacies depend on regional and environmental context, including soil characteristics, regional P surplus and N deposition. Identifying gradients that influence the magnitude of agricultural legacies is key to informing how, where and why forest ecosystems respond to contemporary environmental change.

Passive rewilding is increasingly seen as a promising tool to counterbalance biodiversity losses and recover native forest ecosystems. One key question, crucial to understanding assembly processes and conservation issues underlying land-use change, is the extent to which functional and phylogenetic diversity may recover in spontaneous recent woodlands. Here, we compared understorey plant communities of recent woodlands (which result from afforestation on agricultural lands during the 20th century) with those of ancient forests (uninterrupted for several centuries) in a hotspot of farmland abandonment in western Europe. We combined taxonomic, functional, and phylogenetic diversity metrics to detect potential differences in community composition, structure (richness, divergence), conservation importance (functional originality and specialization, evolutionary distinctiveness) and resilience (functional redundancy, response diversity). The recent and ancient forests harbored clearly distinct compositions, especially regarding the taxonomic and phylogenetic facets. Recent woodlands had higher taxonomic, functional and phylogenetic richness and a higher evolutionary distinctiveness, whereas functional divergence and phylogenetic divergence were higher in ancient forests. On another hand, we did not find any significant differences in functional specialization, originality, redundancy, or response diversity between recent and ancient forests. Our study constitutes one of the first empirical pieces of evidence that recent woodlands may spontaneously regain plant communities phylogenetically rich and functionally resilient, at least as much as those of ancient relict forests. As passive rewilding is the cheapest restoration method, we suggest that it should be a very useful tool to restore and conserve native forest biodiversity and functions, especially when forest areas are restricted and fragmented.

In forest ecosystems, the influence of landscape history on contemporary biodiversity patterns has been shown to provide a convenient framework to explain shifts in plant assemblages. However, very few studies have controlled for present human‐induced activities when analysing the effect of forest continuity on community structures. By cutting and removing trees, foresters substantially change stand ecological conditions, with consequences on biodiversity patterns. Disentangling the effect of past and present human activities on biodiversity is thus crucial for ecosystem management and conservation. We explored the response of plant and springtail species richness and composition to forest continuity (ancient vs. recent) in montane forests, while controlling for stand maturity (mature vs. overmature). We established 70 sites in landscapes dominated by unfragmented ancient forests where we surveyed plants and assessed springtails by analysing environmental DNA. Neither plant nor springtail species richness was influenced by forest continuity or by stand maturity. Instead, site‐specific characteristics, especially soil properties and canopy openness, were of major importance in shaping above‐ and below‐ground richness. For plant and springtail species composition, the effect of forest continuity was mediated by stand maturity. Thus, both plants and springtails showed a convergence in assemblage patterns with the increasing availability of overmature stand attributes. Moreover, soil and stand‐scale factors were evidently more important than landscape‐scale factors in shaping above‐ and below‐ground species composition. Synthesis. We clearly demonstrated that biodiversity patterns are more strongly influenced by present human‐induced activities than by past human‐induced activities. In the Northern Alps where our study sites were located, the colonization credit of most species has been paid off and the transient biodiversity deficit usually related to forest continuity has moved towards equilibrium. These findings emphasize the necessity to better control for local‐scale factors when analysing the response of biodiversity to forest continuity; we call for more research into the effects of forest continuity in unfragmented mountain forests.

Aims Disentangling direct and indirect effects of global change drivers on plant nitrogen (N) uptake in leaves is important for understanding species and community responses in a changing world. Methods We created understorey herb communities on forest soils with and without recent agricultural history. We traced pulse additions of 15 NH 4 15 NO 3 within these mesocosms while applying two-level factorial treatments of N enrichment, warming and illumination. We modelled direct and indirect effects of treatments on leaf N content and 15 N uptake in leaves. Results Warming and illumination had three times larger direct negative effects on leaf N content per dry mass and percentage leaf N derived from label (Ndfl%) than their indirect negative effects via an increasing community cover. These results imply a tissue dilution of N with increasing growth, in response to environmental change directly and indirectly exacerbated by community cover. We additionally found that interspecific differences in Ndfl% correlated with a species’ colonisation capacity and resource acquisition strategy. Conclusions Global change can directly affect allocation of N into foliage, with simultaneous indirect effects via altered community properties that influence individual plant responses. Predicting the future of plant communities in a changing world requires accounting for such understudied pathways.

Plant species of ancient forests tend to be poor dispersers, but recent field studies suggest that dispersal may be strongly accelerated in streams. To further test this idea, we addressed the following two questions: (1) which traits facilitate transport and deposition of seeds by streams? (2) do ancient forest species differ from other forest species with respect to these traits?. In the Boven Slinge, a forested lowland stream in the Netherlands, we measured seed transport and deposition and analysed which traits best explained this. We subsequently compared ancient forest species with other forest species with respect to these key traits. Our field measurements indicated that stream dispersal is determined by both source- and path-related processes. Significance of upstream population size, seed production and seed release period mirrored source effects, whereas significance of buoyancy and seed mass indicated that the path, i.e. stream transport and deposition, further constrains the number of species that can be dispersed by streams. Compared to other forest species, ancient forest species do not differ with respect to seed release period, buoyancy and seed mass, but at a given plant height, ancient forest species produce less seeds than other forest species. This may reflect an adaptation to their relatively stable habitat which comes at the expense of (stream) dispersal capacity. In conclusion, ancient forest plants are just as well equipped for stream dispersal as other forest species, but success will critically depend on upstream population size, given their low per plant seed production.

Summary 1. Worldwide, the floristic composition of temperate forests bears the imprint of past land use for decades to centuries as forests regrow on agricultural land. Many species, however, display significant interregional variation in their ability to (re)colonize post‐agricultural forests. This variation in colonization across regions and the underlying factors remain largely unexplored. 2. We compiled data on 90 species and 812 species × study combinations from 18 studies across Europe that determined species’ distribution patterns in ancient (i.e. continuously forested since the first available land use maps) and post‐agricultural forests. The recovery rate (RR) of species in each landscape was quantified as the log‐response ratio of the percentage occurrence in post‐agricultural over ancient forest and related to the species‐specific life‐history traits and local (soil characteristics and light availability) and regional factors (landscape properties as habitat availability, time available for colonization, and climate). 3. For the herb species, we demonstrate a strong (interactive) effect of species’ life‐history traits and forest habitat availability on the RR of post‐agricultural forest. In graminoids, however, none of the investigated variables were significantly related to the RR. 4. The better colonizing species that mainly belonged to the short‐lived herbs group showed the largest interregional variability. Their recovery significantly increased with the amount of forest habitat within the landscape, whereas, surprisingly, the time available for colonization, climate, soil characteristics and light availability had no effect. 5. Synthesis. By analysing 18 independent studies across Europe, we clearly showed for the first time on a continental scale that the recovery of short‐lived forest herbs increased with the forest habitat availability in the landscape. Small perennial forest herbs, however, were generally unsuccessful in colonizing post‐agricultural forest – even in relatively densely forested landscapes. Hence, our results stress the need to avoid ancient forest clearance to preserve the typical woodland flora.

Aim: Human activity is known to greatly influence species occurrences. In forest ecosystems, biodiversity is often believed to be influenced by two habitat characteristics: (1) forest continuity, related to a minimum length of time in a wooded state since a threshold date; and (2) stand maturity, related to the availability of late-developmental- forest attributes. In a context of ongoing global biodiversity loss, qualifying the effect of past and present human activity on forest ecosystems while taking into account variations in abiotic factors is of primary importance for conservation. Location: Temperate mountain forests in the Northern Alps. Method: Based upon a sampling design crossing forest continuity (ancient vs. Recent) and stand maturity (mature vs. overmature), and while controlling for the effect of two major environmental factors, soil and climate, we explored the individual response of saproxylic beetle, springtail, herbaceous plant and epiphytic macrolichen species to past and present human activity. Results: Forest continuity influenced the occurrence of relatively few species, indicating that past land use had almost no legacy effect on the species occurring in the study forests today. In contrast, stand maturity had an overall positive effect on species occurrences. However, our results showed that species occurrences were more obviously influenced by abiotic conditions. Indeed, beyond the effect of continuity and maturity factors, the probability of presence of numerous species was best explained by climate and soil. Main conclusions: Overall, we show that species occurrence was more influenced by stand maturity than by forest continuity, but also that site-specific characteristics were of great importance in explaining the probability of presence for numerous species. In the ecological context of alpine forests, these findings emphasize the need to better control for climatic and edaphic conditions in order to (1) improve accuracy in predicting species occurrence and (2) better design areas of conservation interest.

Questions: How are epiphytic macrolichen assemblages shaped by forest habitat quality as reflected by the availability of late-developmental forest attributes (i.e., stand maturity) and the temporal continuity of the wooded state (i.e., forest continuity)? Are these two forest habitat features the main drivers of lichen assemblages, and if so, at which spatial scale? Study Site: Temperate mountain forests in the French Northern Alps. Methods: In our sampling design, we defined treatments by crossing forest continuity (ancient vs recent) and stand maturity (mature vs overmature), then quantified lichen response to the treatments at the stand (n = 70) and tree scales (n = 420). We distinguished between total macrolichen and Lobarion species alone. Finally, we assessed the influence of tree-, stand-and landscape-scale variables, as well as climatic variables. Results: Neither total macrolichen nor Lobarion diversity and composition were influenced by forest continuity, stand maturity or by stand-or landscape-associated variables. Instead, climatic variables, light availability at the stand scale and host tree characteristics were the major drivers of lichen assemblages. In our mountain forests, this clearly shows that macrolichen were more influenced by local abiotic and biotic factors than by present or past human-induced activities. Conclusions: Overall, we show that assemblage patterns in forest ecosystems may be driven by parameters that are not directly related to habitat quality. The influences of forest continuity and stand maturity on diversity and composition thus appear to be context-dependent. In the ecological context of alpine forests, these findings highlight the benefits of selective-cutting practices and illustrate the importance of structural heterogeneity, in terms of both improved accessibility to light and tree diameter diversity. Finally, the importance of temperature in shaping assemblage patterns suggests that global warming is probably the most significant threat to macrolichen conservation in temperate mountain forests.

QUESTIONS: (i) Is plant species richness related to patch configuration, quality, heterogeneity and history in very small forest patches? (ii) Is there a similar effect of patch configuration, quality, heterogeneity and history on all plant species or does it vary for different plant groups? (iii) Does the importance of patch configuration, quality, heterogeneity and history vary for plant species richness between patch size classes? LOCATION: Prignitz region, western part of Brandenburg, Germany METHODS: Plant species lists for 183 forest patches (0.08–12.7 ha) were compiled. We conducted a hierarchical partitioning analysis to test which of the four patch variables – configuration, quality, heterogeneity and history – explained most of the variance in plant species richness and richness of various plant groups. RESULTS: Irrespective of patch size class, species richness is mainly predicted by patch quality and heterogeneity. In particular, generalists are primarily affected by the soil moisture and nutrient level, and specialists additionally by patch heterogeneity and history. A higher historical habitat quality, together with long habitat continuity, led to an increase in forest specialists and geophytes in all patches. In the >5‐ha patches only historical habitat quality accounted for a significant increase in the number of species with short‐distance dispersal capacity in all species. Regardless of patch size, the number of locally infrequent species increased significantly with historical habitat quality. The effect of patch configuration was negligible, except for space‐filling trees and shrubs, when considering all patches. CONCLUSIONS: Our more comprehensive statistical approach shows, in general, that all complex variables have an effect on species richness and should be considered in future studies. The fact that patch heterogeneity and quality are the main predictors of species richness indicates that very small forest patches covered a range of highly structured patches and sites having various growth conditions. We assume that the century‐old tradition of private ownership with smallholder social structure is the main reason for variability in stand structure and species assemblage, resulting in the uniqueness of each patch. Since the number of locally infrequent plant species increases significantly with historical habitat quality, we suggest that it is particularly important to consider this variable in future studies on the decline of infrequent plant species.