Michael Scherer-Lorenzen

Remote sensing can link biodiversity and its effects on ecosystem functioning in forests, but in observational studies environmental covariates may confound results. We tested effects of tree species richness and functional diversity on remotely-sensed canopy variables at community and species levels in two forest biodiversity experiments established under homogeneous environmental conditions. At the BIOTREE sites in Kaltenborn and Bechstedt, we combined airborne imaging spectroscopy-based vegetation indices, sun-induced chlorophyll fluorescence, and land surface temperature at 1-m resolution, with ground-based tree stem growth as a productivity measure. At Kaltenborn, increasing species richness (one to four species) did not increase community productivity because of contrasting species-level responses. The normalized difference vegetation index (NDVI) decreased with richness in both needle-leaved species but increased in both broadleaved species. At Bechstedt, increasing functional diversity of mixtures planted with four tree species lowered community-level normalized difference water and photochemical reflectance indices; responses differed between four functional groups of tree species. NDVI was negatively correlated with basal area; correlations among other spectral, thermal, and fluorescence traits varied among tree functional groups. These results show that forest biodiversity experiments can test remotely sensed indicators of tree diversity and ecosystem functioning and inform interpretation of observational studies.

The diversity of many forest-dwelling organisms depends on forest structure, but it remains unknown to which degree this is mediated by microclimatic temperature, and whether microclimatic buffering is universally beneficial for forest biodiversity. In 234 broad-leaved forest plots across nine climatically differing regions in Germany, we measured micro-and macroclimatic temperatures, canopy cover, and deadwood volume after experimental manipulations of forest structure through thinning operations and gap cuts. We surveyed 21 taxonomic groups, representing plants, bacteria, fungi, and animals, to assess how their diversity depended on the predictors. Multi-taxon diversity, and diversity of ten separate taxonomic groups, increased from closed to open canopies. Only necrophagous beetles were more diverse in closed stands. These effects of canopy cover on diversity were partly mediated by microclimatic temperatures. Thereby, diversity responses to microclimatic temperature depended on the macroclimatic context. In regions with colder summers, locally warmer microclimates in canopy gaps had strong positive effects on biodiversity, while these effects were not found in regions with warmer summers. Consequently, management strategies aimed at multi-taxon forest diversity conservation should be chosen based on the regional climate, favoring canopy gaps primarily in colder regions, and taking future climate warming into consideration.

Biodiversity generally enhances ecosystem productivity, but whether such effects persist or intensify during climate extremes is unclear. Here we synthesized data from 75 biodiversity experiments across grasslands and forests to assess how aridity and soil nutrients modulate plant diversity effects under drought and heat extremes. Biodiversity most strongly enhanced productivity under extreme drought in more arid grasslands but had limited effects in forests under such conditions. More arid grasslands showed enhanced complementarity effects under extreme drought, whereas less arid grasslands favoured selection effects driven by productive species. Heat extremes did not produce comparable context-dependent changes in plant diversity effects across ecosystem types or aridity gradients. Soil nutrients did not have any detectable influence under either drought or heat extremes, suggesting that as climatic stress intensifies, hydric limitations override edaphic constraints. Our synthesis identifies when and where plant diversity most strongly enhances productivity, showing that its effects are the greatest under extreme drought in more arid grasslands.

Watersheds are natural units and meta-ecosystems of the earth's land surface providing multiple ecological functions. However, little is known about the biodiversity-ecological multifunctionality relationships of watersheds, particularly regarding how these relationships scale to large and complex landscapes. Here, we explore the impact of forest tree species richness on the ecological multifunctionality of watersheds in terms of carbon sequestration, carbon storage, water supply, water regulation, and soil conservation, by utilizing integrated ground-sourced forest inventory datasets comprising 846 forest watersheds from the Global Forest Biodiversity Initiative, the Global Streamflow Indices and Metadata Archive, and remote sensing data products. We find a consistently positive relationship between forest tree species richness and watershed ecological multifunctionality by accounting for factors such as forest structural characteristics and environmental conditions. Furthermore, we find that this biodiversity-multifunctionality link is dependent on spatial scale and climatic context, becoming stronger in larger watersheds but diminishing in arid climatic conditions. These insights enhance our understanding of ecosystem multifunctionality and underscore the importance of considering watershed-scale ecological processes and biodiversity in ecosystem management and conservation strategies.

Globally, deadwood contains approximately 72 Pg of carbon (C), with around 10.9 Pg C released to the atmosphere annually by decomposers1. This recycling of woody biomass is a crucial source of nutrients underpinning primary productivity in forest systems2, with the long-standing consensus that decay rates are predominantly driven by macroclimate8. However, recent studies suggest that biotic factors such as the composition of local tree or soil communities may play a more important role3–7. In a decomposition experiment across five major forest types in Europe, from the Mediterranean to Boreal forest biome, we show that around 80% of variation in deadwood decay rates occurred within rather than between forest types, and that saprotrophic fungi, protist, and nematode communities explained the highest proportion of variability in deadwood mass loss. Local-scale soil abiotic properties, including soil temperature, were the poorest predictors of decay. These results provide evidence that across a continental gradient, climate is not the dominant predictor of deadwood decay, and that the role of soil biota for rates of decomposition extends beyond the activity of the primary decomposers. Our findings challenge the classical paradigm of climatic control over decomposition by predicting that biotic factors primarily mediate deadwood decay, which are dependent on interactions in the soil microbial food web. Our new insights are pivotal for forecasting terrestrial recycling processes and in highlighting the importance of protecting soil biodiversity, as we show that decomposition strongly depends on the composition and structure of the soil biotic community.

Plants affect terrestrial ecosystem functioning by shaping microenvironments ¹ and by providing the primary production that fuels energy flow into food webs ² . However, how plant community properties affect ecosystem functioning via energy fluxes in food webs has been little studied ^3,4 , especially for the soil food webs that channel most plant-derived energy ^2,5 . Applying a food web energetics approach ^6,7 , we show that the resource economics of dominant tree species control soil food web multifunctionality across European forests. Tree communities dominated by resource-acquisitive species promoted faster rates of multiple soil trophic functions than did communities dominated by resource-conservative species. These effects were primarily driven by higher-quality litter and warmer forest microclimates, leading to increased metabolic activity of soil organisms ⁸ . Accordingly, tree species composition explained a large portion of variation in soil food web multifunctionality, comparable to that explained by biogeographic differences among locations. By contrast, mixtures of three tree species had weakly negative effects relative to single-species stands, mostly due to shifts in energy channelling from living fine roots to litter and a cooling effect on forest microclimate. This occurred despite an overyielding effect in aboveground tree biomass production, suggesting contrasting diversity effects above- and belowground. Our findings emphasize the importance of plant functional traits related to resource economics as drivers of soil food web functioning ^5,9 and demonstrate how climate-driven shifts in tree community composition may alter forest soil functioning.

In the context of anthropogenic eutrophication of the biosphere, understanding the impact of nutrient addition on plant diversity–productivity relationships remains a major challenge. In particular, the indirect effect of nutrient addition on productivity in tree mixtures via changes in the functional structure of tree communities has never been experimentally quantified and may play an important role in mediating diversity–productivity relationships. Here, we present results from young experimental tree communities 4 years after planting, including monocultures and two‐ and four‐species mixtures of six European species ( Acer platanoides, Betula pendula, Larix decidua, Picea abies, Pinus sylvestris and Quercus robur ) with or without 4 years of mineral fertilizer addition. Using a response‐effect trait framework that links plant functional traits with ecosystem processes, we specifically examined how functional diversity (FD) and community weighted means (CWM) of tree height (H) and specific leaf area (SLA) were influenced by fertilization and to what extent they mediated the fertilization effect on above‐ground productivity in woody tissues. The overall fertilization effect on the degree of community‐level overyielding was marginally positive, yet the influence of fertilization varied significantly depending on species composition. Fertilization affected community functional trait structure primarily by increasing CWM of SLA through dominance of species with high SLA, rather than through intraspecific trait variability. Interestingly, the fertilization‐induced change in CWM of SLA reduced community‐level overyielding. Irrespective of fertilization, CWM of H and SLA influenced community‐level overyielding, while FD had no significant effects. Our results indicate that changes in nutrient availability can influence the magnitude of overyielding indirectly through dominance of species with high SLA in young tree communities. This result improves our understanding of the context dependency of diversity–productivity relationships, which strongly depends on nutrient availability influencing the competitive relationships among tree species. The occurrence of such effects early after tree planting could potentially produce long‐term consequences for tree community composition, and even more so in naturally regenerating forests with less control on tree species selection. Read the free Plain Language Summary for this article on the Journal blog.

Functional traits can vary in response to tree species mixing, which in turn might influence biomass production and, consequently, carbon (C) sequestration in diverse forests. However, evidence for consistent broad‐scale patterns in tree trait responses, particularly regarding trait identity and their contribution to above‐ground biomass outcomes, remains limited. Using data from even‐aged forest stands in 11 tree diversity experiments in Europe and Brazil, encompassing 40 tree species, we estimated the influence of species mixing on above‐ground biomass components (woody, litterfall and understory biomass), as well as effects of mixing on plasticity‐driven changes in species‐ and community‐level functional traits. At the community level, specific leaf area (SLA) and leaf area index (LAI) were higher in mixtures than expected values based on monocultures, while leaf nitrogen per area decreased, and leaf nitrogen per mass remained stable. SLA increases were primarily due to the response of less dominant tree species. Woody and litterfall biomass increased in mixtures, whereas understory biomass remained unchanged. At the species level, diversity‐driven plastic changes were observed in multiple traits, but only SLA showed a consistent shift across species. Tree diversity effects on above‐ground biomass were influenced by both functional diversity and diversity‐driven trait shifts, where increased SLA and LAI enhanced woody biomass accumulation, while higher LAI in diverse stands reduced understory biomass. Together, these results show that tree species mixing alters canopy structure and light‐related traits, with shifts in SLA and LAI constituting key pathways through which mixed forests accumulate more woody biomass. Read the free Plain Language Summary for this article on the Journal blog.

Context: Volatile organic compounds (VOCs) create invisible chemical landscapes that influence ecosystem processes. Yet whether VOC β-diversity (i.e., variability in VOC composition between patches) responds to structural heterogeneity and reflects silvicultural habitat management remains unclear. Objectives: In a large field experiment, we quantified how enhanced structural beta complexity (ESBC) affects VOC β-diversity patterns and investigated potential drivers and ecological effects in temperate production forests. Methods: We sampled VOCs in ambient forest air using Tenax/Carboxen adsorbent traps at forest floor and 1 m heights across 234 treatment and control forest patches in six German regions. We analyzed VOCs via thermal desorption-gas chromatography mass-spectrometry (TD-GCMS) and examined environmental drivers including deadwood characteristics, canopy cover, tree species dissimilarity, and herb layer dissimilarity. We tested potential ecological relevance by analyzing saproxylic beetle community responses. Results: VOC β-diversity increased significantly at 1 m height in heterogeneous forests compared to homogeneous forests, but we found no significant change at the forest floor. Deadwood volume and deadwood structural diversity, rather than canopy openness, were identified as the main drivers of increasing VOC β-diversity. Dissimilarity in beetle community composition was associated with VOC β-diversity, but only for forest floor VOCs, suggesting these chemical patterns may correlate with variables beetles respond to. Conclusions: Our findings suggest that volatile β-diversity represents an overlooked dimension of habitat heterogeneity, one that creates invisible chemical heterogeneity influencing inter- and intra-species interactions and ecosystem processes. We demonstrate that enhancing forest heterogeneity through deadwood retention increases both structural heterogeneity and volatile β-diversity.