Site-specific climate responses of soil decomposer biodiversity in forests

Climate change strongly impacts forest ecosystems, exacerbating drought stress, tree mortality, and shifts in species composition. While aboveground changes are well documented, belowground biodiversity and its response to climate-driven alterations remain less studied. Soil-dwelling decomposer organisms such as oribatid mites (Oribatida), earthworms (Lumbricidae), and terrestrial isopods (Oniscidae) play a crucial role in maintaining ecosystem functions through the decomposition of organic matter and nutrient cycling. Abiotic soil conditions drive soil animal communities and the effect of climate change on a forest also depends on soil properties such as water-holding capacity. This study examines the relationship between environmental conditions and decomposer communities in the municipal forest of Darmstadt, Germany, characterized by distinct edaphic and climatic gradients (dry in the West and moist in the East). In the study region, climate change strongly increased tree mortality albeit with high variation across sites. Oribatid mites and earthworms were significantly more abundant in the moister eastern region, while isopods showed no clear abundance differences but higher diversity in the drier west. Decomposer communities were primarily related to soil moisture and tree community composition, with canopy openness playing a crucial role in microclimatic variation. Microclimatic changes in response to tree damage and altered species composition significantly influenced decomposer communities. Drought-prone sites were favored by drought-tolerant taxa, suggesting ongoing shifts in belowground biodiversity. The study underscores the importance of integrating belowground organisms and processes in climate impact assessments in forests to better understand ecosystem resilience and functionality in changing forest environments.