Beyond the role of climate and soil conditions: Living and dead trees matter for soil biodiversity in mountain forests

Abstract

While forests’ contributions to people are intimately linked to their soil biodiversity, little is known about how forest soil biodiversity is structured and influenced by forest characteristics. Living and dead trees influence the quantity and the diversity of resources (e.g. litter content) and habitats (e.g. microclimate) available for soil organisms. In this study, we explored the effects of forest characteristics and their relative importance to regional climate and local soil conditions in explaining forest soil biodiversity.

We characterised forest quantity (abundance of living and dead trees, and dominant tree leaves C/N), and diversity characteristics (tree sizes, deadwood and tree species diversities). We assessed the response of the diversity of 34 soil trophic groups to climate, soil properties and forest characteristics using environmental DNA metabarcoding data along 16 elevational gradients in the French Alps.

Overall, we showed that climate and soil characteristics explained most of the diversity of soil trophic groups. For the diversity of some groups, however, forest characteristics were important drivers (e.g. ectomycorrhizal fungi). In general, forest diversity characteristics had a positive effect on the diversity of soil trophic groups, in agreement with the resource-heterogeneity hypothesis. We also found that the effects of forest characteristics can percolate to high trophic level groups or to groups that do not have a direct link with living or dead trees (e.g. fungivore mites).

Forest characteristics can have complex indirect effects that branch out throughout the whole soil food web. Even if mountain forests span large climatic gradients, forest structure and composition can be additional key drivers of soil biodiversity. Thus forest management, by driving forest structure and composition, can have important effects on soil biodiversity in managed forests.