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Wir Menschen sind auf funktionierende und widerstandsfähige Ökosysteme angewiesen. Der Zustand der Natur in Deutschland hat sich in den letzten Jahrzehnten weiter verschlechtert. Ergänzend zum Schutz der verbliebenen Natur sollte stärker als bisher der Zustand geschädigter Ökosysteme verbessert werden. SRU, WBBGR und WBW geben mit dieser Stellungnahme Empfehlungen für eine wirksame Renaturierungspolitik in Deutschland. Am 23. Mai 2024 wurden die Kernempfehlungen der Stellungnahme in einer öffentlichen Online-Veranstaltung präsentiert und diskutiert. Die Dokumentation ist hier abrufbar. Das Anliegen, die Erholung eines degradierten Ökosystems zu unterstützen, ist weit zu verstehen und umfasst neben der Verbesserung des Zustands von Schutzgebieten auch naturverträgliche Formen der Landnutzung. Ökosysteme sollen sich durch Renaturierung in Richtung naturnäherer Strukturen entwickeln, sodass sie langfristig vielfältige Leistungen erbringen können. Wie andere Vorhaben benötigen Renaturierungsmaßnahmen Flächen. Ökosysteme wiederherzustellen wird daher auch Konflikte um Flächennutzung, wirtschaftliche Aspekte und unser Konsumverhalten mit sich bringen. Die es zu moderieren und zu entscheiden gilt. Renaturierung ist eine gesellschaftliche Aufgabe, die nicht nur den Naturschutz betrifft, sondern vor allem auch die landnutzenden Sektoren, neben der Stadt- und Regionalplanung insbesondere die Landwirtschaft und die Waldbewirtschaftung. Daher zielt diese Stellungnahme darauf ab, Grundzüge einer Renaturierungspolitik zu entwickeln, die Synergien zwischen Naturschutz und Landnutzungsinteressen erzeugt sowie Zielkonflikte minimiert.

Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial for maintaining community productivity over time in both grassland and forest ecosystems.

Purpose of Review International ambitions for massive afforestation and restoration are high. To make these investments sustainable and resilient under future climate change, science is calling for a shift from planting monocultures to mixed forests. But what is the scientific basis for promoting diverse plantations, and what is the feasibility of their establishment and management? As the largest global network of tree diversity experiments, TreeDivNet is uniquely positioned to answer these pressing questions. Building on 428 peer-reviewed TreeDivNet studies, combined with the results of a questionnaire completed by managers of 32 TreeDivNet sites, we aimed to answer the following questions: (i) How and where have TreeDivNet experiments enabled the relationship between tree diversity and tree performance (including productivity, survival, and pathogen damage) to be studied, and what has been learned? (ii) What are the remaining key knowledge gaps in our understanding of the relationship between tree diversity and tree performance? and (iii) What practical insights can be gained from the TreeDivNet experiments for operational, real-world forest plantations? Recent Findings We developed a conceptual framework that identifies the variety of pathways through which target tree performance is related to local neighbourhood diversity and mapped the research efforts for each of those pathways. Experimental research on forest mixtures has focused primarily on direct tree diversity effects on productivity, with generally positive effects of species and functional diversity on productivity. Fewer studies focused on indirect effects mediated via biotic growing conditions (e.g. soil microbes and herbivores) and resource availability and uptake. Most studies examining light uptake found positive effects of species diversity. For pests and diseases, the evidence points mostly towards lower levels of infection for target trees when growing in mixed plantations. Tree diversity effe

Enhancing tree diversity may be important to fostering resilience to drought-related climate extremes. So far, little attention has been given to whether tree diversity can increase the survival of trees and reduce its variability in young forest plantations.We conducted an analysis of seedling and sapling survival from 34 globally distributed tree diversity experiments (363,167 trees, 168 species, 3744 plots, 7 biomes) to answer two questions: (1) Do drought and tree diversity alter the mean and variability in plot-level tree survival, with higher and less variable survival as diversity increases? and (2) Do species that survive poorly in monocultures survive better in mixtures and do specific functional traits explain monoculture survival?Tree species richness reduced variability in plot-level survival, while functional diversity (Rao's Q entropy) increased survival and also reduced its variability. Importantly, the reduction in survival variability became stronger as drought severity increased. We found that species with low survival in monocultures survived comparatively better in mixtures when under drought. Species survival in monoculture was positively associated with drought resistance (indicated by hydraulic traits such as turgor loss point), plant height and conservative resource-acquisition traits (e.g. low leaf nitrogen concentration and small leaf size).Synthesis. The findings highlight: (1) The effectiveness of tree diversity for decreasing the variability in seedling and sapling survival under drought; and (2) the importance of drought resistance and associated traits to explain altered tree species survival in response to tree diversity and drought. From an ecological perspective, we recommend mixing be considered to stabilize tree survival, particularly when functionally diverse forests with drought-resistant species also promote high survival of drought-sensitive species.

Bei der Begrenzung des Klimawandels hat die Reduktion der Treibhausgasemissionen oberste Priorität. Um jedoch das Ziel der Treibhausgasneutralität zu erreichen, benötigen wir zusätzlich Verfahren, die der Atmosphäre dauerhaft Kohlendioxid (CO2) entziehen. An Land stehen uns dafür biologische, chemische und geochemische Entnahmemethoden zur Verfügung. Bevor jedoch über ihren Einsatz entschieden werden kann, müssen Nutzen, Kosten und mögliche Risiken erforscht und anschließend gegeneinander abgewogen werden. Ein Factsheet des Forschungsprogramms CDRterra über CO2-Entnahmeverfahren an Land.

Wälder sind von großer Bedeutung für den Naturhaushalt und erbringen vielfältige Ökosystemleistungen. Vor allem die Folgen des Klimawandels lassen diese Fähigkeiten jedoch zunehmend schwinden und stellen damit auch bisherige Bewirtschaftungskonzepte und Wertschöpfungsketten infrage. Vor diesem Hintergrund hat eine Expert:innengruppe im Auftrag der Bundesministerien für Ernährung und Landwirtschaft (BMEL) sowie für Bildung und Forschung (BMBF) Vorschläge erarbeitet, um die nationale Forschung im Bereich Wald und Holz neu auszurichten und zu strukturieren. Unter anderem wird die Gründung eines nationalen Zentrums für Wald- und Holzforschung empfohlen. Das Konzept wurde heute durch die Leiter der Expert:innengruppe, Prof. Folkhard Isermeyer (Thünen-Institut) und Prof. Georg Teutsch (UFZ), an die zuständigen Bundesministerien übergeben. Anlass für die Einsetzung der Expert:innengruppe waren vor allem die Folgen des Klimawandels, die in vielen Wäldern deutlich sichtbar sind und die Wirtschaft, Gesellschaft und Politik vor neue Herausforderungen stellen. Um wissensbasiert darauf reagieren zu können, etwa bei der Abschätzung von Risiken oder der Entwicklung von Strategien für den Schutz und die nachhaltige Nutzung von Wäldern, ist Forschung gefragt.  Die Gruppe identifizierte vier Themenbereiche, in denen es mit Blick auf die Folgen des Klimawandels besonders wichtig erscheint, die Forschung zu stärken und gemeinsame Strategien für die Wald- und Holzwirtschaft in Deutschland zu entwickeln: (1) Zukunftskonzepte für die Waldbewirtschaftung, (2) Extremereignisse und Krisenmanagement, (3) Holzbasierte Bioökonomie und (4) Holz im Bauwesen.  Um konkrete, wissensbasierte Lösungsoptionen für die Wald- und Holzwirtschaft der Zukunft zu liefern, sollten die Forschungseinrichtungen neue Maßstäbe in der Kooperation untereinander setzen und dabei wissenschaftliche Exzellenz mit höchster praktischer Relevanz verbinden. Die Expert:innengruppe schlägt daher vor, ein nati

As of 2020, the world has an estimated 290 million ha of planted forests and this number is continuously increasing. Of these, 131 million ha are monospecific planted forests under intensive management. Although monospecific planted forests are important in providing timber, they harbor less biodiversity and are potentially more susceptible to disturbances than natural or diverse planted forests. Here, we point out the increasing scientific evidence for increased resilience and ecosystem service provision of functionally and species diverse planted forests (hereafter referred to as diverse planted forests) compared to monospecific ones. Furthermore, we propose five concrete steps to foster the adoption of diverse planted forests: (1) improve awareness of benefits and practical options of diverse planted forests among land-owners, managers, and investors; (2) incentivize tree species diversity in public funding of afforestation and programs to diversify current maladapted planted forests of low diversity; (3) develop new wood-based products that can be derived from many different tree species not yet in use; (4) invest in research to assess landscape benefits of diverse planted forests for functional connectivity and resilience to global-change threats; and (5) improve the evidence base on diverse planted forests, in particular in currently under-represented regions, where new options could be tested.   &nbsp

Forests perform various important ecosystem functions that contribute to ecosystem services. In many parts of the world, forest management has shifted from a focus on timber production to multi-purpose forestry, combining timber production with the supply of other forest ecosystem services. However, it is unclear which forest types provide which ecosystem services and to what extent forests primarily managed for timber already supply multiple ecosystem services. Based on a comprehensive dataset collected across 150 forest plots in three regions differing in management intensity and species composition, we develop models to predict the potential supply of 13 ecosystem services. We use those models to assess the level of multifunctionality of managed forests at the national level using national forest inventory data.

1. Mixed-species forests have often been shown to enhance above-ground ecosystem properties and processes. Despite the significance of fine roots for tree and ecosystem functioning, the role of tree species diversity for below-ground processes driven by fine roots remains largely unknown. Previously, an underyielding of fine-root biomass (FRB) in tree mixtures across four major European forest types has been reported. To explain this phenomenon, we tested here the effect of tree species mixing on fine-root traits related to soil exploitation efficiency, including biotic feedbacks from ectomycorrhizal fungi (EcM), and assessed the role of root trait dissimilarity. 2.We analysed morphological and chemical traits as well as ectomycorrhizal colonisation intensity of absorptive fine roots (i.e. first three most distal orders) in soil samples from 315 mixed and mono-specific tree neighbourhoods in mainly mature, semi-natural forest stands across Europe. Additionally, we quantified mycorrhizal abundance and diversity in soil samples from the same stands. 3. At the community level, fine roots in tree mixtures were characterised by higher specific root lengths and root nitrogen concentrations, lower diameters, and root tissue densities indicating a faster resource acquisition strategy compared to mono-specific stands. The higher root EcM colonisation intensity and soil EcM diversity in mixtures compared to mono-specific stands may further provide evidence for positive biotic feedbacks. Moreover, the diversity of fine-root traits influenced FRB, as mixtures characterised by a higher trait dissimilarity were linked to a lower reduction in FRB. At the level of phylogenetic groups, thin-rooted angiosperm species showed stronger responses to mixing than thick-rooted gymnosperms, especially in terms of root morphology and EcM colonisation, indicating different strategies of response to tree mixing. 4. Our results indicate that a lower FRB can reflect a shift in soil resource acqui

Global change exposes forest ecosystems to many risks including novel climatic conditions, increased frequency of climatic extremes and sudden emergence and spread of pests and pathogens. At the same time, forest landscape restoration has regained global attention as an integral strategy for climate change mitigation. Owing to unpredictable future risks and the need for new forests that provide multiple ecosystem services, mixed-species forests have been advocated for this purpose. However, the successful establishment of mixed forests requires intrinsic knowledge of biodiversity's role for forest ecosystem functioning. In this respect, a better understanding of tree-tree interactions and how they contribute to observed positive tree species richness effects on key ecosystem functions is critical. Here, we review the current knowledge of the underlying mechanisms of tree-tree interactions and argue that positive net biodiversity effects at the community scale may emerge from the dominance of positive over negative interactions at the local neighbourhood scale. In a second step, we demonstrate how tree-tree interactions and the immediate tree neighbourhood's role can be systematically assessed in a tree diversity experiment. The expected results will improve predictions about the effects of tree interactions on ecosystem functioning based on general principles. We argue that this knowledge is urgently required to guide the design of tree species mixtures for the successful establishment of newly planted forests.

At the global scale, most forest research on biodiversity focuses on aboveground organisms. However, understanding the structural associations between aboveground and belowground communities provides relevant information about important functions linked to biogeochemical cycles. Microorganisms such as soil fungi are known to be closely coupled to the dominant tree vegetation, and we hypothesize that tree traits affect fungal guilds and soil functionality in multiple ways. By analyzing fungal diversity of 64 plots from four European forest types using Illumina DNA sequencing, we show that soil fungal communities respond to tree community traits rather than to tree species diversity. To explain changes in fungal community structure and measured soil enzymatic activities, we used a trait‐based ecological approach and community‐weighted means of tree traits to define “fast” (acquisitive) vs. “slow” (conservative) tree communities. We found specific tree trait effects on different soil fungal guilds and soil enzymatic activities: Tree traits associated with litter and absorptive roots correlated with fungal, especially pathogen diversity, and influenced community composition of soil fungi. Relative abundance of the symbiotrophic and saprotrophic guilds mirrored the litter quality, while the root traits of fast tree communities enhanced symbiotroph abundance. We found that forest types of higher latitudes, which are dominated by fast tree communities, correlated with high carbon‐cycling enzymatic activities. In contrast, Mediterranean forests with slow tree communities showed high enzymatic activities related to nitrogen and phosphorous. Our findings highlight that tree trait effects of either “fast” or “slow” tree communities drive different fungal guilds and influence biogeochemical cycles.

Current studies show that multispecies forests are beneficial regarding biodiversity and ecosystem functionality. However, there are only little efforts to understand the ecological mechanisms behind these advantages of multispecies forests. Bacteria are among the key plant growth‐promoting microorganisms that support tree growth and fitness. Thus, we investigated links between bacterial communities, their functionality and root trait dispersion within four major European forest types comprising multispecies and monospecific plots. Bacterial diversity revealed no major changes across the root functional dispersion gradient. In contrast, predicted gene profiles linked to plant growth activities suggest an increasing bacterial functionality from monospecific to multispecies forest. In multispecies forest plots, the bacterial functionality linked to plant growth activities declined with the increasing functional dispersion of the roots. Our findings indicate that enriched abundant bacterial OTUs are decoupled from bacterial functionality. We also found direct effects of tree species identity on bacterial community composition, but no significant relations with root functional dispersion. Additionally, bacterial network analyses indicated that multispecies forest have a higher complexity in their bacterial communities, which points towards more stable forest systems with greater functionality. We identified a potential of root dispersion to facilitate bacterial interactions and consequently, plant growth activities.

Forest ecosystem functioning generally benefits from higher tree species richness, but variation within richness levels is typically large. This is mostly due to the contrasting performances of communities with different compositions. Evidence-based understanding of composition effects on forest productivity, as well as on multiple other functions will enable forest managers to focus on the selection of species that maximize functioning, rather than on diversity per se. We used a dataset of 30 ecosystem functions measured in stands with different species richness and composition in six European forest types. First, we quantified whether the compositions that maximize annual above-ground wood production (productivity) generally also fulfil the multiple other ecosystem functions (multifunctionality). Then, we quantified the species identity effects and strength of interspecific interactions to identify the “best” and “worst” species composition for multifunctionality. Finally, we evaluated the real-world frequency of occurrence of best and worst mixtures, using harmonized data from multiple national forest inventories. The most productive tree species combinations also tended to express relatively high multifunctionality, although we found a relatively wide range of compositions with high- or low-average multifunctionality for the same level of productivity. Monocultures were distributed among the highest as well as the lowest performing compositions. The variation in functioning between compositions was generally driven by differences in the performance of the component species and, to a lesser extent, by particular interspecific interactions. Finally, we found that the most frequent species compositions in inventory data were monospecific stands and that the most common compositions showed below-average multifunctionality and productivity. Synthesis and applications. Species identity and composition effects are essential to the development of high-performing product

TreeDivNet is the largest network of biodiversity experiments worldwide, but needs to expand. We encourage colleagues to establish new experiments on the relation between tree species diversity and forest ecosystem functioning, and to make use of the platform for collaborative research.

While the number of studies on the role of biodiversity on ecosystem functioning is steadily increasing, a key component of biogeochemical cycling in forests, dead wood decay, has been largely neglected. It remains widely unknown whether and how dead wood decay is affected by diversity loss in forests. We studied the hierarchical effects of tree species diversity on wood decay rates in a subtropical forest landscape in southeast China via its influence on fungal OTU richness and invertebrate diversity using piecewise structural equation models. The experiment was conducted in natural forest plots that span a wide gradient of tree species diversity embedded in a heterogeneous topography. To account for interactions between macro‐invertebrates and fungi, that potentially modify the influence of tree biodiversity and climate on dead wood decay, we compared a macro‐invertebrate exclusion treatment with a control treatment that allowed access to all types of decomposers. Diversity effects of trees on wood decay rates were mostly negative and mediated by the diversity of macro‐invertebrates. However, the effects of tree species diversity or fungal OTU richness and macro‐invertebrate diversity on wood decay rates were comparatively weak. Temperature affected decay rates positively and had the strongest influence in all treatments. While the exclusion of macro‐invertebrates did not lead to a reduction of wood decay rates, our results suggest that they may however have a mediating role in the process. In the presence of invertebrates the predictability of wood decay rates was higher and we observed a tendency of a stronger temperature control. Our results suggest that there is evidence for diversity effects on wood decomposition, but the temperature control is still more important. Thus, an increase in mean annual temperature will increase carbon and nutrient turnover through wood decomposition in subtropical forest irrespective of biotic composition.

While forest management strongly influences biodiversity, it remains unclear how the structural and compositional changes caused by management affect different community dimensions (e.g. richness, specialisation, abundance or completeness) and how this differs between taxa. We assessed the effects of nine forest features (representing stand structure, heterogeneity and tree composition) on thirteen above‐ and belowground trophic groups of plants, animals, fungi and bacteria in 150 temperate forest plots differing in their management type. Canopy cover decreased light resources, which increased community specialisation but reduced overall diversity and abundance. Features increasing resource types and diversifying microhabitats (admixing of oaks and conifers) were important and mostly affected richness. Belowground groups responded differently to those aboveground and had weaker responses to most forest features. Our results show that we need to consider forest features rather than broad management types and highlight the importance of considering several groups and community dimensions to better inform conservation.

Trade-offs and synergies in the supply of forest ecosystem services are common but the drivers of these relationships are poorly understood. To guide management that seeks to promote multiple services, we investigated the relationships between 12 stand-level forest attributes, including structure, composition, heterogeneity and plant diversity, plus 4 environmental factors, and proxies for 14 ecosystem services in 150 temperate forest plots. Our results show that forest attributes are the best predictors of most ecosystem services and are also good predictors of several synergies and trade-offs between services. Environmental factors also play an important role, mostly in combination with forest attributes. Our study suggests that managing forests to increase structural heterogeneity, maintain large trees, and canopy gaps would promote the supply of multiple ecosystem services. These results highlight the potential for forest management to encourage multifunctional forests and suggest that a coordinated landscape-scale strategy could help to mitigate trade-offs in human-dominated landscapes.

Biodiversity experiments have shown that species loss reduces ecosystem functioning in grassland. To test whether this result can be extrapolated to forests, the main contributors to terrestrial primary productivity, requires large-scale experiments. We manipulated tree species richness by planting more than 150,000 trees in plots with 1 to 16 species. Simulating multiple extinction scenarios, we found that richness strongly increased stand-level productivity. After 8 years, 16-species mixtures had accumulated over twice the amount of carbon found in average monocultures and similar amounts as those of two commercial monocultures. Species richness effects were strongly associated with functional and phylogenetic diversity. A shrub addition treatment reduced tree productivity, but this reduction was smaller at high shrub species richness. Our results encourage multispecies afforestation strategies to restore biodiversity and mitigate climate change.

Despite the important role of wood-inhabiting fungi (WIF) in deadwood decomposition, our knowledge of the factors shaping the dynamics of their species richness and community composition is scarce. This is due to limitations regarding the resolution of classical methods used for characterizing WIF communities and to a lack of well-replicated long-term experiments with sufficient numbers of tree species. Here, we used a large scale experiment with logs of 11 tree species at an early stage of decomposition, distributed across three regions of Germany, to identify the factors shaping WIF community composition and Operational Taxonomic Unit (OTU) richness using next generation sequencing. We found that tree species identity was the most significant factor, corresponding to (P < 0.001) and explaining 10% (representing 48% of the explainable variance) of the overall WIF community composition. The next important group of variables were wood-physicochemical properties, of which wood pH was the only factor that consistently corresponded to WIF community composition. For overall WIF richness patterns, we found that approximately 20% of the total variance was explained by wood N content, location, tree species identity and wood density. It is noteworthy that the importance of determinants of WIF community composition and richness appeared to depend greatly on tree species group (broadleaved vs. coniferous) and it differed between the fungal phyla Ascomycota and Basidiomycota.

Nitrogen deposition can strongly affect biodiversity, but its specific effects on terrestrial microbial communities and their roles for ecosystem functions and processes are still unclear. Here, we investigated the impacts of N deposition on wood‐inhabiting fungi (WIF) and their related ecological functions and processes in a highly N‐limited deadwood habitat. Based on high‐throughput sequencing, enzymatic activity assay and measurements of wood decomposition rates, we show that N addition has no significant effect on the overall WIF community composition or on related ecosystem functions and processes in this habitat. Nevertheless, we detected several switches in presence/absence (gain/loss) of wood‐inhabiting fungal OTUs due to the effect of N addition. The responses of WIF differed from previous studies carried out with fungi living in soil and leaf‐litter, which represent less N‐limited fungal habitats. Our results suggest that adaptation at different levels of organization and functional redundancy may explain this buffered response and the resistant microbial‐mediated ecosystem function and processes against N deposition in highly N‐limited habitats.