Benjamin M. Delory

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.

Although habitat heterogeneity is known to enhance local species diversity, the effects of management‐driven structural heterogeneity on understorey plant communities across spatial scales remain poorly understood, despite their crucial role for forest biodiversity and ecosystem functioning. To analyse how forest understorey plant communities respond to an enhancement of structural heterogeneity in managed forests, we established 11 experimental sites consisting of two paired forest landscapes, an untreated homogenous control and a treatment district (ESBC, Enhancement of Structural Beta‐Complexity). In treatment districts, structural heterogeneity was enhanced through different combinations of local patch‐scale manipulations of light and deadwood features, leading to greater between‐patch heterogeneity at the landscape scale. We performed a meta‐analysis across these 11 sites using a Hill‐Chao number and sample coverage standardisation framework. Gamma diversity increased across taxonomic, functional and phylogenetic facets in structurally heterogeneous forests (ESBC districts) via higher alpha diversity. This effect was positively associated with heterogeneity in light availability between forest patches, but not with their mean light availability. In contrast, we found no evidence supporting that species turnover among patches (i.e. beta diversity) significantly contributes on average to the observed increase in gamma diversity. However, both the direction and magnitude of beta diversity responses varied substantially among study sites. On average, structurally heterogeneous forests supported higher species richness for both open and closed forest habitat species. Synthesis and applications . Our findings highlight the benefits of enhancing structural heterogeneity for understorey plant diversity in managed forest landscapes. Specifically, management strategies that create a spatial mosaic of interventions, such as combining single‐tree removal with gap felling, can increase the variety of light niches among forest patches, thereby supporting the conservation of a wide range of understorey plant species, including forest specialists.

Specialized metabolites released in the environment mediate ecological interactions across geographic scales and levels of biological organization. Whereas chemodiversity-the richness, relative abundance and disparity of specialized compounds within a blend of metabolites-has received substantial interest at the level of pairwise interactions, much less is known about how metabolites produced by multiple individuals and species merge into higher-level blends at population, community and ecosystem scales. Here we review evidence for emergent functions that arise from such higher-level chemodiversity: how blends can change in composition and functional consequence as they move through air, water and soil, and vary in time and space, thereby creating a dynamic chemodiversity landscape. We further discuss the applied potential of these chemodiversity landscapes and the threats that could compromise them. We outline key questions that will help to guide research on how higher-level chemodiversity contributes to ecological processes and functioning across scales.

Forest ecosystem productivity is affected by tree species richness and may be further modulated by different mycorrhizal fungal types, for example, arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi, which strongly affect soil processes. Productivity and soil processes are linked through leaf litterfall, a major pathway for carbon and nutrient input to soils. Higher tree diversity and contrasting mycorrhizal strategies may enhance the variability and heterogeneity of litterfall quantity and quality, yet the combined effects of tree species richness and mycorrhizal type mixtures on the temporal dynamics and spatial distribution of litterfall remain underexplored. We investigated leaf litterfall dynamics over 1 year in the 8‐year‐old MyDiv tree diversity experiment, spanning a gradient of tree species richness (one, two, four species) and mycorrhizal treatments (AM, EM, AM+EM). Monthly litterfall production and nutrient concentrations were measured, and annual wood production (i.e. wood biomass increment) was assessed to quantify aboveground biomass allocation to wood and litter. Tree species richness did not affect annual production of wood or leaf litter. In contrast, annual wood production varied with mycorrhizal types, being highest in EM tree communities, whereas mycorrhizal type did not affect annual leaf litterfall. However, litterfall dynamics were influenced by both tree species richness and mycorrhizal type. Specifically, higher tree diversity extended the litterfall period and increased spatial variability (CV) of litterfall at the meter scale, while temporal variability remained unaffected. Phosphorus concentration in leaf litter differed among mycorrhizal types, with the highest values observed in AM communities. Species‐rich stands exhibited lower C:P and N:P ratios in leaf litter and greater phosphorus fluxes. Contrary to expectations, mixed mycorrhizal communities did not produce more leaf litter than monotypic combinations (AM or EM tree species). Synthesis: Our findings show that leaf litterfall dynamics are modified by tree species richness and mycorrhizal type. The increased spatial variability of litterfall at the meter scale and the extended litterfall period associated with higher tree species richness could create a wider range of resource niches for soil organisms in time and space. This may promote the diversity and activity of the decomposer community, ultimately strengthening overall forest nutrient cycling.

Extensive knowledge exists on plant‐species traits and functions, but we understand less about how population‐ or community‐level emergent traits influence ecosystem functioning. This knowledge gap is important for ecosystems like peatlands, arid drylands, salt marshes, seagrass meadows, and mangroves, where emergent traits of plant communities can create plant‐environment feedbacks that amplify or dampen ecosystem processes. Recent insights from restoration ecology suggest that these feedbacks can critically influence restoration success. Despite growing recognition of emergent trait‐driven feedbacks in other ecosystems, they remain underexplored in peatland restoration, the world's most carbon‐dense ecosystem. Here, we review emergent self‐amplifying and self‐dampening feedbacks with net positive effects for peat moss‐dominated systems. We show how these feedbacks can promote key physical, chemical, and biological processes that enhance peat moss growth, increase water retention, and reduce microbial decomposition of organic matter. Understanding and fostering these feedbacks offers a promising framework to accelerate peatland restoration across diverse degradation states.

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.

Metacommunity theory has expanded our understanding of how spatial dynamics and local interactions influence species communities. Different assembly archetypes, reflecting different roles of species differences, habitat differences, and dispersal have been described, but we lack empirical studies specifically in terrestrial habitats testing which archetype is most important. In a replicated design, we experimentally enhanced structural between‐patch heterogeneity in homogeneous production forests and developed a statistical framework controlling for sample incompleteness to detect different metacommunity processes. Meta‐analyses on > 100 K individuals of > 1.3 K beetle species showed an increase of ~60 species in heterogenized forests at γ‐level promoted by increasing α‐diversity consistent with the mass‐effect and an increase of β‐diversity by ~10% supporting species‐sorting . Additionally, we tested β‐deviations from random assembly as a proxy of neutral processes . Findings indicate that enhancing structural heterogeneity can shift forests from patch‐dynamics dominance towards mass‐effect and species‐sorting , offering a promising pathway to restore biodiversity in managed landscapes.

Forest microclimates, their dependence on forest structure, and their impact on biodiversity are crucial for future forest management under climate change. However, standard approaches for measuring forest microclimates do not capture within-plot heterogeneity, which, according to the habitat heterogeneity hypothesis, is a key driver of local biodiversity. We quantified horizontal and vertical microclimatic heterogeneity within 30 broad-leaved forest plots in Central Europe using a three-dimensional design with high spatial resolution. Moreover, we examined whether microclimatic heterogeneity differs among silvicultural treatments and whether it can be predicted using forest structure indices derived from laser scanning. Additionally, we explored the relationship between microclimatic heterogeneity and biodiversity. In the understory of canopy gaps, warm and cold habitats co-existed in close proximity, leading to a high horizontal microclimatic heterogeneity. In closed stands with high structural complexity, we found steep gradients of increasing temperature and vapor pressure deficit from the ground to the canopy during mid-day. Canopy cover and forest structural complexity were strong indicators of microclimatic heterogeneity. We found positive relationships between herb layer temperature heterogeneity and the diversity of plants, Hymenoptera, and Diptera. Our results demonstrate that single-point measurements fail to capture the substantial microclimatic heterogeneity within plots, potentially misrepresenting the conditions experienced by forest species. However, laser scanning provides reliable indicators for within- plot microclimatic heterogeneity. With canopy gaps featuring high horizontal microclimatic heterogeneity and promoting the biodiversity of several taxonomic groups, we argue that managing forests for maximized temperature buffering should not be the only strategy to conserve forest biodiversity. Highlights: High small-scale horizontal microclimatic heterogeneity in canopy gaps Steep vertical microclimatic gradients in closed-canopy forests Canopy cover and structural complexity: indicators for microclimatic heterogeneity Positive relationship between herb layer temperature heterogeneity and biodiversity