Effects of logging and non-native tree proliferation on the birds overwintering in the upland forests of north-western Italy

Abstract

Factors associated with management and logging practices are of particular interest in the perspective of biodiversity management. In this study we focused on overwintering birds of two close and contrasting forest habitats: a 60–120 years old oak forest and a secondary 10–20 years old wood that has lost most of its original vegetation because of continuous logging and is now dominated by an introduced species, black locust Robinia pseudoacacia. We examined bird use of the forests over two levels: species–habitat relationships and foraging niches. The former were assessed by means of point counts centred in 50 m radius plots, whereas the latter by observations of foraging behaviour and plant species exploitation. Mean species richness, diversity and abundance of bark foragers was significantly greater in the old-growth stand, where trees were higher and larger but stem density was lower. Almost no wintering bird species occurred at higher density in the second-growth than in old-growth forest, and no foraging birds positively selected the black locust as substrate. Despite the observed differences in biodiversity metrics and plant species exploitation, most birds of the two stands showed few shifts in their foraging behaviour (in terms of foraging technique, substrate, relative horizontal and vertical position) and niche metrics (breadth and overlap). By considering results obtained with the two approaches, we suggest that biodiversity of altered secondary woods can be increased if current silvicultural practices are modified towards (1) maintaining oaks or trees prone to snag formation such as old poplars and (2) preventing black locust establishment in post-clearcut communities.