Heathland health is deteriorating across Northwestern Europe due to various threats which commonly are the result of global change drivers and inadequate management. Varying traditional management practices have been modified to counteract this development, all of which have inevitable trade-offs in terms of promoting associated biodiversity, ecosystem functions and services. These trade-offs are mainly between low (low biomass/soil removal) and high (large biomass/soil removal) intensity management practices. Here we analysed the impacts of low (mowing) versus a newly developed high intensity (scarification, i.e. mowing with subsequent moss removal) management practice on spider diversity, as an excellent bioindicator for habitat quality shifts due to environmental change. We sampled spiders at 15 plots, 5 replicates of the two management practices each, as well as 5 unmanaged controls in the Lüneburg Heath, Northern Germany, one year after the management was implemented. No spider species showed aversion to mowed plots likely due to the increased habitat heterogeneity provided by mowing, while spider abundance and functional richness responded negatively to the increased homogeneity induced by scarification. However, scarification benefited some critically endangered specialists such as Psimmitis sabulosa due to their preference for high bare soil cover. Therefore, managing heathlands with a mosaic of mowed and scarified patches could likely promote spider diversity and protect threatened species while limiting negative effects on functional diversity. Since our results apply to the effect of management on spider biodiversity only one year after the management has been implemented, future research should focus on how these effects change over time.

IntroductionBending the biodiversity curve and meeting international commitments like the Kunming-Montreal Agreement and the EU Nature Restoration Law require scaling up ecological restoration across spatial, temporal, and societal dimensions. Achieving this depends on a strong scientific evidence base and synthesis of effective practices from both ecological and social perspectives.ObjectivesThe Grassworks project investigates factors influencing grassland restoration success in Germany by integrating ecological, socioeconomic, and social-ecological perspectives.MethodsWe assessed previously restored grasslands across three regions along a north-south gradient in Germany, comparing them to reference sites. A stratified design evaluated restoration outcomes based on methods, past land use, management, governance, finance, and time since intervention. We analyzed vegetation, pollinators, soil, and economic performance while considering landscape configuration. Social-ecological aspects, including stakeholder values, knowledge exchange, and decision-making networks, were also examined. A Real-World Laboratory approach integrated ex ante and ex post evaluations, demonstration sites, and co-created restoration activities.ResultsWe propose a replicable, adaptable framework for social-ecological restoration, synthesizing key ecological, economic, and social dimensions to support continuous learning and adaptive management, facilitating more effective and scalable restoration practices.ConclusionsDrawing from the Grassworks project, this research provides insights to inform and guide future large-scale restoration efforts, promoting a holistic and evidence-based approach to social-ecological restoration worldwide.

One of the most endangered plant communities in Germany, and one that is on the verge of extinction, is the lichen pine forest (Cladino-Pinetum sylvestris, syn. Cladonio-Pinetum sylvestris). For this reason, it has been selected by the Floristisch-soziologische Arbeitsgemeinschaft as the "Plant Community of the Year 2025". Lichen pine forests are unproductive, sparse and understorey-poor coniferous forest ecosystems, mainly in the planar and colline altitudinal zone. The soils are extremely nutrient-poor and acidic, usually very dry with a poorly developed humus layer. Lichen pine forests occur on outwash plains, moraines, dunes and valley sands, but also in mountainous areas with granite, quartzite or sandstone as parent rock. In Germany, this forest type is currently found only in small areas, mainly in sub-continental regions. Lichen pine forests occur mainly in the northeastern German inland lowlands from the Elbe valley in Lower Saxony eastward (Mecklenburg-Western Pomerania, Saxony-Anhalt, Brandenburg) as well as in Middle Franconia and Upper Palatinate (Bavaria). In addi-tion to open woodlands with species of grey hair-grass swards (Corynephorion), there are lichen pine forests with almost no vascular plants and others with Vaccinium species, transitioning to the more widespread blueberry pine forests. Lichen pine forests represent a biodiversity hotspot in Central Europe for ground-dwelling fruticose lichens, especially reindeer lichens and other members of the genus Cladonia. They also host a variety of other lichens, bryophytes and macrofungi, and are impor-tant for faunal biodiversity. They represent an Annex I habitat type under the EU Habitats Directive (code 91T0). Lichen pine forests are at the beginning of natural forest development on immature soils on sand or quartz-rich rocks and have been strongly promoted by litter-raking and sod-cutting, and sometimes by grazing. They probably reached their greatest extent in the 19th and early 20th centuries. After the abandonment of the historical forest use, current stands are highly endangered, mainly by eutrophication due to natural succession and airborne nitrogen loads. Since the 1990s lichen pine forests in Germany have lost about 90 % of their former area. With an increased nutrient availability, com-petitive pleurocarpous mosses, sometimes dwarf shrubs and the wavy hair-grass, spread and displace the typical lichens and small-growing bryophytes. Other threats include land use (sand and stone mining, building areas), active forest conversion, a lack of morphodynamics and, in recent years, prolonged periods of heat and drought. Existing stands, some of which on the verge of extinction, must not only be protected from direct destruction, but also require active protection measures, similar to many open-land habitats. The restoration of lichen pine forests is only possible by removing the litter (together with the humus layer) and subsequently inoculating the raw soil with lichen fragments. First results from restoration projects in the Elbe valley of Lower Saxony and in Middle Franconia are presented. With these, we would like to encourage local and regional actors and conservationists to take appropriate action. In sand pits and quarries, refraining from recultivation measures can promote the formation of new lichen pine forests.

Plant communities are being exposed to changing environmental conditions all around the globe, leading to alterations in plant diversity, community composition, and ecosystem functioning. For herbaceous understorey communities in temperate forests, responses to global change are postulated to be complex, due to the presence of a tree layer that modulates understorey responses to external pressures such as climate change and changes in atmospheric nitrogen deposition rates. Multiple investigative approaches have been put forward as tools to detect, quantify and predict understorey responses to these global-change drivers, including, among others, distributed resurvey studies and manipulative experiments. These investigative approaches are generally designed and reported upon in isolation, while integration across investigative approaches is rarely considered. In this study, we integrate three investigative approaches (two complementary resurvey approaches and one experimental approach) to investigate how climate warming and changes in nitrogen deposition affect the functional composition of the understorey and how functional responses in the understorey are modulated by canopy disturbance, that is, changes in overstorey canopy openness over time. Our resurvey data reveal that most changes in understorey functional characteristics represent responses to changes in canopy openness with shifts in macroclimate temperature and aerial nitrogen deposition playing secondary roles. Contrary to expectations, we found little evidence that these drivers interact. In addition, experimental findings deviated from the observational findings, suggesting that the forces driving understorey change at the regional scale differ from those driving change at the forest floor (i.e., the experimental treatments). Our study demonstrates that different approaches need to be integrated to acquire a full picture of how understorey communities respond to global change.

Aims: We introduce ReSurveyEurope - a new data source of resurveyed vegetation plots in Europe, compiled by a collaborative network of vegetation scientists. We describe the scope of this initiative, provide an overview of currently available data, governance, data contribution rules, and accessibility. In addition, we outline further steps, including potential research questions. Results: ReSurveyEurope includes resurveyed vegetation plots from all habitats. Version 1.0 of ReSurveyEurope contains 283,135 observations (i.e., individual surveys of each plot) from 79,190 plots sampled in 449 independent resurvey projects. Of these, 62,139 (78%) are permanent plots, that is, marked in situ, or located with GPS, which allow for high spatial accuracy in resurvey. The remaining 17,051 (22%) plots are from studies in which plots from the initial survey could not be exactly relocated. Four data sets, which together account for 28,470 (36%) plots, provide only presence/absence information on plant species, while the remaining 50,720 (64%) plots contain abundance information (e.g., percentage cover or cover-abundance classes such as variants of the Braun-Blanquet scale). The oldest plots were sampled in 1911 in the Swiss Alps, while most plots were sampled between 1950 and 2020. Conclusions: ReSurveyEurope is a new resource to address a wide range of research questions on fine-scale changes in European vegetation. The initiative is devoted to an inclusive and transparent governance and data usage approach, based on slightly adapted rules of the well-established European Vegetation Archive (EVA). ReSurvey:Europe data are ready for use, and proposals for analyses of the data set can be submitted at any time to the coordinators. Still, further data contributions are highly welcome.

Carbon sequestration by trees is crucial to mitigate the effects of the current climate crisis. The extent to trees sequester and allocate carbon to above- or belowground structures in turn is mediated by neighbouring species. Although many studies have demonstrated positive effects of diverse neighbourhoods on a tree's productivity, little is known about biomass allocation responses to mono- vs. heterospecific neighbourhoods. In the present study we quantified above- and belowground biomass production and root-to-shoot ratios (RSR) of trees grown in mono- and heterospecific neighbourhoods. To this end we analysed growth of mono- and heterospecific tree species pairs (TSPs) established in a greenhouse and a field experiment. In the greenhouse experiment response variables were measured after one year of growth after sapling harvest. In the field experiment, conducted in the context of a forest biodiversity experiment in subtropical China, we analysed biomass density and RSR over three years using terrestrial laser scanner and minirhizotrons. RSR of trees in heterospecific TSPs were significantly higher than in monospecific TSPs. In the greenhouse experiment, this was related to a stronger below- than aboveground overyielding in heterospecific TSPs. In the field experiment, trees in heterospecific TSPs showed a stronger increase in aboveground investments over time than in monospecific TSPs, indicating that positive diversity effects became stronger for aboveground structures with progressing tree development. Our findings are consistent with the optimal biomass partitioning theory and highlight the importance of tree-tree interactions on biomass allocation. Higher RSR in mixtures further suggest a higher resistance or resilience of tree saplings against environmental stressors related to climate change (drought, heat waves). ### Competing Interest Statement The authors have declared no competing interest.

Global warming is increasing the frequency and intensity of climate extremes. Forests may buffer such extreme events by creating their own microclimate below their canopy via cooling hot and insulating against cold macroclimate air temperatures. This buffering capacity of forests may be increased by tree diversity and may itself maintain forest functioning and biodiversity. However, despite its relevance for many ecosystem processes, the effect of tree diversity on temperature buffering is largely unexplored. Here, we show that tree species richness consistently increases forest temperature buffering across daily, monthly, and annual scales over six years. This finding is based on data from a large-scale tree diversity experiment covering a species richness gradient of 1 to 24 tree species. We found that species richness strengthened both components of forest temperature buffering: the attenuation of hot and of cold macroclimate air temperatures, with the cooling effect being more pronounced. The buffering effect of tree species richness was mediated by canopy density and structural diversity, assessed as leaf area index and stand structural complexity index, respectively. Safeguarding and planting diverse forests may thus mitigate negative effects of global warming and climate extremes on ecosystem functions and communities below the tree canopy.### Competing Interest StatementThe authors have declared no competing interest.

Understanding the mechanisms underlying diversity-productivity relationships (DPRs) is crucial to mitigating the effects of forest biodiversity loss. Tree-tree interactions in diverse communities are fundamental in driving growth rates, potentially shaping the emergent DPRs, yet remain poorly explored. Here, using data from a large-scale forest biodiversity experiment in subtropical China, we demonstrated that changes in individual tree productivity were driven by species-specific pairwise interactions, with higher positive net pairwise interaction effects on trees in more diverse neighbourhoods. By perturbing the interactions strength from empirical data in simulations, we revealed that the positive differences between inter- and intra-specific interactions were the critical determinant for the emergence of positive DPRs. Surprisingly, the condition for positive DPRs corresponded to the condition for coexistence. Our results thus provide a novel insight into how pairwise tree interactions regulate DPRs, with implications for identifying the tree mixtures with maximized productivity to guide forest restoration and reforestation efforts.

Since 2019 the 'Floristisch-soziologische Arbeitsgemeinschaft' (FlorSoz) has annually nominated the 'plant community of the year', to draw attention to Germany's endangered plant communities in need of protection. This campaign specifically aims at supporting the conservation of plant communities and their habitats as well as at promoting political and administrative decisions and implementation processes that serve to protect and restore these ecosystems. Calthion palustris meadows will be the plant community of the year 2024. Formerly common in cultural landscapes throughout western and Central Europe, wet meadows with marsh-marigold (Caltha palustris) have become rare in most regions. Large-scale drainage and other measures of agricultural intensification, including the conversion of wetlands to intensive grassland and arable land, are responsible for the strong decline of this valuable meadow type in recent decades. Increased fertilization on the one hand and abandonment of marginal sites on the other led to changes in species composition and species loss. As an essential part of our cultural landscape, wet meadows are endangered and in some regions even threatened with extinction. Here, we outline the phytosociology of Calthion plant communities, their ecological characteristics, biodiversity and species composition. We provide an overview of the ecology, distribution and conservation status of the communities. Calthion wet meadows support a variety of mostly widely distributed, but locally rare and endangered plant species. They offer habitat to numerous vulnerable animal species, especially invertebrates and birds. With the decline of wet meadows, numerous ground-nesting bird species typical of this habitat, especially waders, have also declined. As marsh-marigold wet meadows are of high ecological and functional importance and deserve prioritised protection, the causes of their decline are explained in detail. Furthermore, we discuss the ecological context of preservation, suitable conservation measures and options for restoration. Reclamation of abandoned wetlands can be considered a promising path for restoration. However, nutrient removal and rewetting of agriculturally improved grasslands, are often more difficult to implement. Diaspores have to be actively introduced and costly measures to raise groundwater levels such as sealing ditches or removing drainage systems are necessary. The short-term reduction of excessive nutrient levels is often impossible. Approaches promoting non-intensive use of wet meadows are discussed and suggestions are made to actively optimising the financial and advisory framework. For this purpose, better programs for nature conservation contracts, higher funding and other supporting instruments are essential. With the proclamation of Calthion wet meadows as plant community of the year and the publication of this paper, we intend to support conservationists and people committed to improving the general political conditions for the implementation of measures on local, regional, national and international levels. Those farmers who have managed wet meadows sustainably for decades despite adverse trends towards increased production growth deserve recognition and encouragement to maintain the traditional management. Successful measures to protect and restore species-rich wetlands are urgently needed.

Vegetation-plot resurvey data are a main source of information on terrestrial biodiversity change, with records reaching back more than one century. Although more and more data from re-sampled plots have been published, there is not yet a comprehensive open-access dataset available for analysis. Here, we compiled and harmonised vegetation-plot resurvey data from Germany covering almost 100 years. We show the distribution of the plot data in space, time and across habitat types of the European Nature Information System (EUNIS). In addition, we include metadata on geographic location, plot size and vegetation structure. The data allow temporal biodiversity change to be assessed at the community scale, reaching back further into the past than most comparable data yet available. They also enable tracking changes in the incidence and distribution of individual species across Germany. In summary, the data come at a level of detail that holds promise for broadening our understanding of the mechanisms and drivers behind plant diversity change over the last century.

In order to communicate issues relating to the protection of plant communities and their habitats more effectively to the general public, the Floristisch-Soziologische Arbeitsgemeinschaft (FlorSoz) has proclaimed a "Plant Community of the Year" since 2019 and an explanatory text is published. This is intended to point out communities that are critically endangered, to provide targeted support for political and administrative decision-making and implementation processes for the conservation of the diversity of ecosystems and plant communities in Germany. For the year 2023, the vegetation of amphibious plants in nutrient-poor lowland waters (Littorelletea uniflorae p.p.) has been selected. Such vegetation of Littorella and related plant communities is threatened with extinction in Germany due to eutrophication, habitat loss and climate change. Protection and restoration measures are therefore urgently needed. This article provides a brief overview of the conservation significance of the Littorelletea vegetation, their floristic-sociological characteristics, main drivers for their decline and suitable countermeasures.

Many recent studies have analysed plant species responses to environmental change, but interactive effects of global change drivers and how they are modulated by biotic interactions are still poorly understood. In a mesocosm experiment, we studied the interactive effects of nitrogen (N) fertilization and drought events on plant growth and how these effects are shaped by competitive interactions, using a segetal plant community typical of the lowlands of central Europe (composed of Lilium bulbiferum (segetal species) and Secale cereale (crop species)). We expected that N fertilization increases the drought sensitivity of Lilium (negative interaction effect), and that these effects are shaped by interspecific competition with Secale. Secale and Lilium showed opposing responses to N fertilization (second year of the experiment): Whilst Secale aboveground and belowground biomass almost doubled with N fertilization, Lilium aboveground and belowground biomass showed no response or decreased, respectively, providing Secale with a competitive advantage. Lilium aboveground tissue dieback (as a proxy for growth vigour) was 22% in N and 35% in drought treatments (control: 6%), but reached 91% when combining these treatments. Increasing Lilium tissue dieback was strongly related to decreasing belowground (root) biomass, caused by both negative direct effects of combined treatments (N fertilization + drought), and negative indirect effects acting via treatment-induced increase in Secale biomass. Our results demonstrate that competitive interactions can shape the effects of global change drivers on plant growth. This knowledge in turn could be important for plant species conservation, particularly in the face of ongoing shifts in environmental conditions.

Reforestation in sloping terrain is an important measure for soil erosion control and sustainable watershed management. The mechanical stability of such reforested stands, however, can be low due to a strong asymmetric shape of tree crowns. We investigated how neighbourhood tree species richness, neighbourhood pressure, tree height, and slope inclination affect crown asymmetry in a large-scale plantation biodiversity-ecosystem functioning experiment in subtropical China (BEF-China) over eight years. We took the advantage of terrestrial laser scanning (TLS) measurements, which provide non-destructive, high-resolution data of tree structure without altering tree interactions. Neighbourhood species richness significantly reduced crown asymmetry, and this effect became stronger at steeper slopes. Our results suggest that tree diversity promotes the mechanical stability of forest stands in sloping terrain and highlight the importance of TLS-data for a comprehensive understanding of the role of tree diversity in modulating crown interactions in mixed-species forest plantations.

Forest structural complexity has been identified as an important driver for promoting simultaneously biodiversity across trophic levels and multiple ecosystem services. However, we still have a limited understanding of the processes that lead to structural complex stands and how they evolve over time. Using terrestrial laser scanning (TLS), we quantified a three-dimensional (3D) stand structural complexity index (SSCI) in an experimental plantation with a long gradient of tree species richness (1-24 species). The plantation was established in 2009, and we made use of a multi-temporal TLS dataset recorded during 2012-2019. We found a positive relationship between tree species richness and structural complexity. This relationship became stronger over time. Ten years after planting, SSCI was on average two-fold higher in 16- and 24-species mixtures than in monocultures. Furthermore, we demonstrate that tree species richness promotes 3D stand structural complexity indirectly by fostering a high vertical heterogeneity and thus greater spatial complementarity in canopy space. Synthesis and applications. Our findings indicate that tree species richness plays a crucial role in promoting stand structural complexity in young plantations, and this role becomes more important already during early stand development. Thus, afforestation measures would benefit from planting multiple native tree species to initiate structurally complex stands.

As woody plants provide much of the trophic basis for food webs in forests their species richness, but also stand age and numerous further variables such as vegetation structure, soil properties and elevation can shape assemblages of ground beetles (Coleoptera: Carabidae). However, the combined impact of these numerous variables on ground beetle diversity and community structure has rarely been studied simultaneously. Therefore, ground beetles were studied in 27 plots in a highly diverse and structurally heterogeneous subtropical forest ecosystem, the Gutianshan National Park (southeast China) using pitfall traps and flight interception traps. Both trapping methods collected partly overlapping species spectra. The arboreal fauna was dominated by lebiines and to a smaller extent by tiger beetles and platynines; the epigeic fauna comprised mostly representatives of the genus Carabus and numerous tribes, especially anisodactylines, pterostichines, and sphodrines. Ground beetle species richness, abundance, and biomass of the pitfall trap catches were analyzed with generalized linear mixed models (GLMMs), fitted with seven environmental variables. Four of these variables influenced the ground beetle assemblages: Canopy cover, herb cover, pH value of the topsoil and elevation. Contrary to our expectations, woody plant species richness and stand age did not significantly affect ground beetle assemblages. Thus, ground beetles seem to respond differently to environmental variables than ants and spiders, two other predominantly predatory arthropod groups that were studied on the same plots in our study area and which showed distinct relationships with woody plant richness. Our results highlight the need to study a wider range of taxa to achieve a better understanding of how environmental changes affect species assemblages and their functioning in forest ecosystems.

Extreme climatic events threaten forests and their climate mitigation potential globally. Understanding the drivers promoting ecosystem stability is therefore considered crucial for mitigating adverse climate change effects on forests. Here, we use structural equation models to explain how tree species richness, asynchronous species dynamics, species-level population stability, and drought-tolerance traits relate to the stability of forest productivity along an experimentally manipulated species richness gradient ranging from 1 to 24 tree species. Tree species richness improved community stability by increasing asynchrony. That is, at higher species richness, interannual variation in productivity among tree species buffered the community against stress-related productivity declines. This effect was positively related to variation in stomatal control and resistance-acquisition strategies among species, but not to the community-weighted means of these trait syndromes. The identified mechanisms by which tree species richness stabilizes forest productivity emphasize the importance of diverse, mixed-species forests to adapt to climate change.