Biology subjects

Rothacher, J.

Publications and source records attributed to Rothacher, J..

8 recordsLinked to original sources

bioRxiv2025

Microclimatic heterogeneity is associated with forest structural complexity and biodiversity

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. HighlightsO_LIHigh small-scale horizontal microclimatic heterogeneity in canopy gaps C_LIO_LISteep vertical microclimatic gradients in closed-canopy forests C_LIO_LICanopy cover and structural complexity: indicators for microclimatic heterogeneity C_LIO_LIPositive relationship between herb layer temperature heterogeneity and biodiversity C_LI

ecology↗

bioRxiv2025

The Invisible Heterogeneity of a Forest -- Beta Diversity of Volatiles

Forest structural heterogeneity affects biodiversity, yet how changes in forest structure influence the spatial patterns of forest chemical heterogeneity remains poorly understood. Volatile organic compounds (VOCs) create invisible chemical landscapes that influence forest ecosystem processes, but whether VOC {beta}-diversity patterns respond to silviculture or disturbance caused heterogeneity remains unknown. We quantified how enhanced structural beta complexity (ESBC) treatments affect VOC {beta}-diversity patterns and investigated potential drivers and ecological effects in temperate production forests. Using the experimental BETA-FOR framework, we sampled ambient forest air at the forest floor and 1 m heights across 234 forest patches in six German regions using Tenax/Carboxen adsorbent traps analyzed via TD-GCMS. Results from generalized linear beta regression models showed that {beta}-diversity of VOCs increased significantly at 1 m height in ESBC forests compared to control forests, but this increase was not significant at the forest floor. In contrast to studies on plants, fungi and animals, the main driver for increasing beta-diversity in VOCs was not the heterogeneity of canopy openness, but the amount of deadwood. Using saproxylic beetles as a test group, we found that saproxylic beetle community dissimilarity increased with VOC dissimilarity, but only for forest floor VOCs. Our finding adds a new component to the framework of habitat heterogeneity, the invisible gradient of volatile diversity utilized by many forest organisms. Furthermore, we provide the first evidence that enhancing the heterogeneity of forests, and particularly of the dead wood, increase not only the structural heterogeneity but also the volatile {beta}-diversity.

ecology↗

bioRxiv2025

Old growth attributes by chain saw: how between-patch heterogeneity changes the metacommunities of beetles in temperate forests

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 >100K individuals of >1.3K beetle species showed an increase of [~]60 species in heterogenized forests at {gamma}-level promoted by increasing -diversity consistent with the mass-effect and an increase of {beta}-diversity by [~]10% supporting species-sorting. Additionally, we tested {beta}-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.

ecology↗

bioRxiv2025

Temperate forest heterogeneity decreases local and landscape-scale spider diversity through habitat filtering despite species turnover

O_LISpiders are key components of forest food webs, making use of the three-dimensional forest structure. Yet modern silviculture has homogenized temperate forest structure at local and landscape scales. The consequences of this homogenization for landscape-level spider diversity, however, remain largely unknown. C_LIO_LITherefore, we sampled spiders using pitfall traps across 234 patches in a large-scale, replicated field experiment at 11 paired European beech (Fagus sylvatica) forest sites in Germany. In one district per site, we experimentally diversified between-forest-patch complexity (ESBC) through canopy gap creation and deadwood enrichment and kept a second district untreated as a structurally homogeneous control. C_LIO_LIWe applied a novel meta-analytic framework to compare -, {beta}-, and {gamma}-diversity of spiders between treatment and control districts, standardized for sample coverage, along Hill numbers giving increasing weight to abundance and for taxonomic, functional, and phylogenetic diversity. To gain a deeper insight into the effects of our intervention on the processes affecting the assembly of spider communities, we investigated the response of functional-phylogenetic diversity quantified by standardized effect sizes of mean pairwise distances (SES MFPD) to our treatments. C_LIO_LIBased on 18,540 spider individuals from 206 species, treatment districts exhibited significantly lower {gamma}- and -diversity across all diversity facets and Hill numbers, particularly when focusing on rare species (q = 0). In contrast, {beta}-diversity increased in treatment districts for phylogenetic and functional diversity across all Hill numbers (q = 0, 1, 2). Although spider abundances were higher in treatment patches, functional-phylogenetic diversity decreased in gaps and ESBC districts in general, indicating a shift from limiting similarity towards habitat filtering. C_LIO_LIOur findings corroborate earlier results of high abundances but lower taxonomic and functional diversity in canopy gaps due to strong habitat filtering effects, resulting in overall lower -diversity, which cannot be compensated by increasing {beta}-diversity. Hence, the greater three-dimensional complexity of homogeneous forests supports more diverse spider metacommunities at the {gamma}-scale, particularly when controlling for sample coverage, suggesting that canopy spider diversity in temperate forests may be underestimated. Nonetheless, higher abundances in treatment districts point to increased predator pressure and greater prey availability in structurally diversified forests. C_LI

ecology↗

bioRxiv2025

Higher bat and bird γ-diversity in structurally complex forests is driven by distinct α- and β-diversity responses

Effective conservation management and habitat restoration rely on understanding how biodiversity responds to environmental change. Centuries of silviculture have homogenized forests and their species communities globally, reducing biodiversity. To test whether restoring forest structural complexity can promote biodiversity, we conducted a large-scale, spatially explicit landscape experiment. At 11 sites across Germany, we compared bat and bird diversity in forests with experimentally enhanced heterogeneity by increasing deadwood and canopy complexity to homogeneous production forests. Both taxa were investigated by autonomous acoustic recorders and automatic species identification. We quantified within-patch (-), between-patch ({beta}-), and landscape-level ({gamma}-) diversity, emphasizing infrequent to highly frequent species for taxonomic, functional, and phylogenetic diversity. The pairwise comparisons of the sites were synthesized using a newly developed meta-analysis of rarefaction-extrapolation curves. {gamma}-diversity increased significantly in structurally heterogeneous forests for both taxa, albeit through distinct taxon-specific mechanisms. Bat {gamma}-diversity gains were primarily driven by higher {beta}-diversity, indicating greater dissimilarity in species assemblages among patches, while bird {gamma}-diversity increased via higher -diversity within patches. Bat diversity increases were mainly taxonomic, suggesting functional similarity in the communities, whereas birds showed the highest gains in functional diversity, indicating that experimental treatments resulted in greater trait dissimilarity. Our results provide experimental evidence under real-world conditions that {gamma}-diversity can be shaped by different diversity mechanisms. These patterns likely originate from differences in activity ranges, such as the large-scale movements of foraging bats in contrast to the more spatially restricted, territorial behavior of birds. This highlights the need for taxon-specific restoration strategies in homogenized landscapes.

ecology↗

bioRxiv2025

Experimental enhancement of structural heterogeneity in forest landscapes promotes multidimensional hoverfly diversity.

O_LIThe homogenization of temperate forests due to intensive management has led to biodiversity loss at local and landscape scales, threatening species persistence and ecosystem functions. However, experimental evidence on how structural heterogeneity among forest patches influences diversity at the landscape scale is lacking. Here, we test whether enhancing structural heterogeneity, via diverse deadwood enrichment and canopy gap creation treatments (Enhancement of Structural Beta Complexity, ESBC), can increase hoverfly diversity within landscapes, and elucidate the contributions of local (-) diversity enrichment and turnover ({beta}-diversity) to this effect. C_LIO_LIWe conducted a large-scale forest experiment in 11 regions across Germany. Each region included two districts, representing small forest landscapes. In one district, we implemented patches with ESBC treatments, while in the other, serving as the control, we established patches without ESBC. Hoverflies were sampled in three seasonal intervals and across, in total, 234 forest patches (50 x 50 m) using pan traps. We applied a new integrative meta-analytic framework that incorporates sample completeness to quantify taxonomic, functional, and phylogenetic diversity (TD, FD, PD) using Hill numbers at , {beta}, and {gamma} scales. C_LIO_LIAll three {gamma}-diversity dimensions - TD, FD, and PD - were significantly higher in structurally heterogeneous forest landscapes than in homogeneous ones. The strongest effects were observed for TD, indicating functional and phylogenetic redundancy among species. Effect sizes declined with increasing order of Hill numbers, suggesting that rare species benefit most from structural heterogeneity. C_LIO_LIIn most regions, {gamma}-diversity gains were driven by increases in -diversity rather than {beta}-diversity, highlighting the importance of interventions to increase local structural complexity. However, several regions also showed elevated {beta}-diversity, indicating context-dependent effects of spatial heterogeneity. C_LIO_LIOur results provide the first experimental evidence that enhancing structural heterogeneity at the landscape scale can restore multi-dimensional insect diversity in temperate forests. They underscore the management value of ESBC as a scalable tool to restore biodiversity, increase ecological resilience, and counteract biotic homogenization in production forests. C_LI

ecology↗

bioRxiv2025

Dung beetles do not profit from enhanced spatial heterogeneity in production forests: a large-scale forest manipulation experiment

O_LICentral European forest management strategies promoting structurally homogeneous closed-canopy forests have led to landscape-level declines in biodiversity and ecosystem multifunctionality. Conservation-targeted management programs aim at reintroducing structural heterogeneity into production forests, however, it is not well understood if species diversity and ecosystem functions generally profit from management promoting heterogeneity in forest structure. By removing and processing mammalian dung remains, dung beetles play an integral role in ecosystem functions in forests. C_LIO_LIIn one of the largest manipulative forest experiments in Central Europe to date, we analysed the effects of enhanced structural heterogeneity in production forests, climate, and mammalian defecation on dung beetle diversity and dung removal rates at the local and landscape level. We assessed communities of dung beetles and dung removal rates on 234 study patches (50 x 50 m) in eleven paired forest landscapes across a climatic gradient in Germany. Forest landscapes were either managed to conserve a homogeneous closed canopy or to create a heterogeneous forest structure with forest patches varying in canopy coverage and dead wood availability. C_LIO_LIWe did not find that more heterogeneously managed forests had higher dung beetle species diversity and dung removal rates. Canopy openings did not increase species turnover but decreased species diversity. C_LIO_LIAlong the climate gradient, dung beetle average biomass and dung removal decreased with increasing temperature. Canopy openings in combination with higher temperatures negatively impacted all abundant dung beetle species, but especially the large species Anoplotrupes stercorosus, comprising > 90% of the total dung beetle biomass. C_LIO_LISynthesis and application: Our results suggest that dung beetles do not profit from management increasing the structural heterogeneity of forests. Due to a restricted climate and habitat niche of the current Central European dung beetle fauna, future warming and openings in forest structure might have negative effects on dung beetles and consequently on the ecosystem services they provide in Central European production forests. C_LI

ecology↗

bioRxiv2025

A short cut to sample coverage standardization in meta-barcoding data provides new insights into land use effects on insect diversity

The use of metabarcoding for insect species identification has grown rapidly, but the absence of abundance data hinders meaningful diversity metrics like sample coverage-standardized species richness. Additionally, the vast number of taxa often lacks a unified phylogeny or trait database. We present a framework for constructing a phylogenetic tree encompassing the majority of insect families, standardisation of sample coverage (an objective measure of sample completeness) and assessment of both taxonomic and phylogenetic diversity using the Hill series for metabarcoding data. Applied to central Europe, our framework analysed insect diversity from 400 families along a land-use gradient. Results revealed land-use intensity significantly affects sample coverage, emphasizing the need for biodiversity standardization. After standardization, taxonomic diversity declined by 27-44%, and phylogenetic diversity by 13-29% across 39,000 Operational Taxonomic Units, from forests to agricultural areas. Rare species exhibited greater phylogenetic diversity loss than taxonomic, while dominant species showed smaller phylogenetic losses but stronger declines in taxonomic diversity. Our findings underscore agricultures detrimental effects on specific insect taxa, even after adjusting for sample coverage, and provide new insights into the loss of functional diversity, as represented by phylogeny.

ecology↗