COS 17-2 - Local drivers of tree-related microhabitats diversity and impact on biodiversity in the Ciron riparian forest

Background/Question/Methods

Tree-related microhabitats (hereafter TreMs) are key features for biodiversity conservation in forest ecosystems. The occurrence and diversity of TreMs are related to several factors such as stand composition or age. As forestry practices can lead to a loss of TreM-bearing trees and of their associated biodiversity, it is fundamental to identify factors explaining TreMs occurrence and diversity in order to better integrate them into forest management. Here we study ecological factors driving diversity and occurrence of TreMs at different spatial scales and we investigate the relationships between those factors, TreMs and biodiversity. Our study was carried out in the Ciron valley (Aquitaine, South West of France) where the near-natural riparian forest is bordered by single-species pine plantations of the Landes forest. Along the river and some of its tributaries, 29 sites were selected according to a forest structure complexity gradient. Each of them were subdivided into 3 delineated plots (about 0,1 ha each) along a topographic gradient (“flood plain”, slope and plateau). In each plot, TreMs and forest structure and composition were inventoried. Birds and wild bees (Hymenoptera, Apoidea) were respectively surveyed by listening points and pan traps.

Results/Conclusions

Preliminary results suggest that drivers of TreMs diversity and abundance occur at different spatial scales. At larger scales, forest structure and composition, including the number of tree species, the proportion of dead trees or of maritime pines in the plot, affect the diversity and abundance of TreMs. At the tree scale, tree species, diameter at breast height and status (dead/alive) seem also to influence diversity and occurrence of TreMs. At first sight, results also suggest that birds and wild bees richness and abundance could depend on forest structure and composition. These preliminary results will be further developed and discussed. The results of this study could provide a better knowledge on TreMs occurrence and diversity. It can also provide an insight of the impact of pine plantations and management on TreMs and biodiversity in the Landes forest and more precisely along the Ciron river which encompasses a Natura2000 area into the riparian forest. These results could allow to highlight essential factors to take into account in management and conservation schemes and support previous studies claiming that TreMs are relevant biological indicators.