Influence of tree characteristics and forest management on tree microhabitats

Higher densities of tree microhabitats in unmanaged forests may explain biodiversity differences with managed forests. To better understand the determinants of this potential biodiversity indicator, we studied the influence of tree characteristics on a set of tree microhabitats (e.g. cavities, cracks, bark features) on 75 plots in managed and unmanaged French forests. We hypothesized that the number of different microhabitat types per tree and the occurrence of a given microhabitat type on a tree would be higher in unmanaged than in managed forests, and that this difference could be linked to individual tree characteristics: diameter, vitality and species. We show that unmanaged forests contained more trees likely to host microhabitats (i.e. large trees, snags) at the stand level. However, at the tree level, forest management did not influence microhabitats; only tree characteristics did: large trees and snags contained more microhabitats. The number and occurrence of microhabitats also varied with tree species: oaks and beech generally hosted more microhabitats, but occurrence of certain types of microhabitats was higher on fir and spruce. We conclude that, even though microhabitats are not equally distributed between managed and unmanaged forests, two trees with similar characteristics in similar site conditions have the same number and probability of occurrence of microhabitats, whatever the management type. In order to preserve biodiversity, foresters could reproduce unmanaged forest features in managed forests through the conservation of specific tree types (e.g. veteran trees, snags). Tree microhabitats could also be more often targeted in sustainable forest management monitoring. (C) 2010 Elsevier Ltd. All rights reserved.