Daniel Kraus

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.

Given increasing deer populations and rising canopy openness through tree mortality in European forests, understanding how these changes affect above‐belowground communities and ecosystem functioning is becoming more important. Earthworms comprise the largest animal biomass in European forest soils and play a central role in decomposition, carbon and nutrient cycling, and soil formation. However, their responses to canopy openness and deer browsing have been studied almost exclusively in northern North America, where interactions involve white‐tailed deer ( Odocoileus virginianus ) and mainly non‐native and invasive earthworms. Here, we examine how roe deer ( Capreolus capreolus ) and canopy openness interactively affect native earthworm communities in a temperate European forest across 75 experimental patches: 54 closed‐canopy and 21 experimentally created canopy‐gap patches. Five years after gap establishment, we sampled earthworms and associated environmental variables from two plots per patch: exclosure (fenced) and control (unfenced) plots. We found that roe deer and canopy gaps interactively influenced earthworm communities. Under closed canopy, roe deer reduced earthworm biomass and density. If roe deer were absent, canopy gaps had no effect on earthworms, but if roe deer were present, canopy gaps increased biomass and density through vegetation‐mediated pathways and enhanced soil water content. The magnitude of these effects differed among earthworm ecological groups (anecic species, i.e., earthworms that create deep, permanent burrows and connect surface litter with deeper soil layers, vs. endogeic species, i.e., earthworms that live and feed entirely within the soil) and life stages (juveniles vs. adults). Indirect effects of roe deer were particularly beneficial for juveniles. These results contrast with patterns reported for white‐tailed deer and non‐native earthworms in northern North American forests, where white‐tailed deer presence typically promotes earthworms. Our results on the direct and indirect effects of roe deer on belowground earthworms shed new light on the complex interactions of deer populations and canopy structure on forest soil biodiversity and ecosystem functioning.

Browsing by ungulates directly influences understorey plant communities through selective removal of certain species and indirectly by modifying plant competition, environmental conditions and successional dynamics. In Central Europe, roe deer ( Capreolus capreolus ) are the most widely distributed ungulate species forming locally dense populations. Understanding the effects of roe deer is essential for sustainable forest management, particularly in the context of changing environmental conditions such as increased tree mortality and expanding canopy gaps. To disentangle the direct effects of roe deer from indirect environmental modifications, we investigated the herb layer (vascular plants n = 54) or within experimental gaps ( n = 21) and were surveyed 5 years after their establishment. Roe deer increased herb layer species richness overall, but reduced functional diversity in closed forests. Canopy gaps decreased herb layer species richness but increased shrub layer cover. Soil pH was independently positively associated with herb layer species richness, but not with functional diversity and to a lesser extent with shrub layer cover. Structural equation models showed that canopy gaps increased light availability 1 m aboveground, but this effect was counteracted by already increased shrub layer cover. By reducing shrub layer cover, roe deer indirectly increased herb layer species richness. Roe deer presence directly reduced herb layer functional diversity, but also indirectly mitigated this negative effect by lowering shrub cover and thereby increasing light availability. Synthesis . Forest gaps primarily reshape herb layer composition by increasing light availability and shrub layer encroachment. Roe deer influence herb layer community assembly both directly and indirectly via modification of the shrub layer and light availability and thus shifting plant–plant competition. These findings emphasize the complex role of browsers in structuring herb layer communities and help to understand how changes in roe deer populations and canopy gaps will shape the future of temperate European forests.

Tree-related microhabitats (TreMs) describe the microhabitats that a tree can provide for a multitude of other taxonomic groups and have been proposed as an important indicator for forest biodiversity (Asbeck et al., 2021). So far, the focus of TreM studies has been on temperate forests, although many trees in the tropics harbour exceptionally high numbers of TreMs. In this study, TreMs in the lowland tropical forests of the Choco (Ecuador) and in the mountain tropical forests of Mount Kilimanjaro (Tanzania) were surveyed. Our results extend the existing typology of TreMs of Larrieu et al. (2018) to include tropical forests and enabled a comparison of the relative recordings and diversity of TreMs between tropical and temperate forests. A new TreM form, Root formations, and three new TreM groups, concavities build by fruits or leaves, dendrotelms, and root formations, were established. In total, 15 new TreM types in five different TreM groups were specified. The relative recordings of most TreMs were similar between tropical and temperate forests. However, ivy and lianas, and ferns were more common in the lowland rainforest than in temperate forests, and bark microsoil , limb breakage, and foliose and fruticose lichens in tropical montane forest than in lowland rainforest. Mountain tropical forests hosted the highest diversity for common and dominant TreM types, and lowland tropical forest the highest diversity for rare TreMs. Our extended typology of tree-related microhabitats can support studies of forest-dwelling biodiversity in tropical forests. Specifically, given the ongoing threat to tropical forests, TreMs can serve as an additional tool allowing rapid assessments of biodiversity in these hyperdiverse ecosystems.