Regional-scale response of earthworm assemblages to forest tree density experimental manipulation across a stand age gradient of sessile oak forests
Réponse des assemblages de vers de terre à la gestion de la densité du peuplement : une évaluation à large échelle sur un gradient d'âge
Résumé
Global warming imposes new constraints on forest ecosystems and induces forest management adaptation. Consequently, the French forest policy currently promotes a reduction of stand density to face increasing summer droughts risk and provide higher supply of firewood. However, few studies have yet assessed the potential impact of this forest management intensification on soil biodiversity. We conducted a regional-scale assessment of earthworm assemblages response to forest tree density experimental manipulation. Paired plots treated using silvicultural-thinning regimes of contrasting intensity and located thoughout nine French forests encompassing a wide gradient of stand age and pedoclimatic context were studied (33 plots). Though tree density manipulation had not effect on the overall earthworm abundance and diversity, a shift in the community composition was observed. The different responses depending on earthworm species considered were related to their ecological traits. While litter-dwelling, i.e. epigeic, earthworms were unaffected by tree density manipulation, soil-dwelling species had constrated responses. Hence, endogeic earthworms abundance and diversity showed a strong increase with tree density reduction whereas anecic earthworms abundance tend to decrease. This may highlights a shift in litter supply location, with higher proportion of belowground litter, i.e. dead roots, with the reduction of tree canopy due to higher understory vegetation cover. Earthworm assemblages response to forest tree density was consistent over the stand age gradient. This change of earthworm community composition may have important consequences on ecosystem processes such as litter decomposition, forest floor and soil carbon dynamic, soil structuration and water regime and the subsequent supply of forest goods and services.