Bird community response in mountain pine forests of the Pyrenees managed under a shelterwood system

Abstract

Understanding the effects of forest management on biodiversity is a vital challenge given the current regime of large-scale socio-ecological drivers affecting forest ecosystems and their multifunctionality. Here we assessed how forest management affects abundances of common breeding birds in mountain pine (Pinus uncinata Ram. ex DC) stands in the Pyrenees. We assessed, at guild level, avian response to changes in stand structure across different management stages in forests managed under a shelterwood system, as well as in unmanaged forests. Bird guilds were based on habitat breadth, nesting habitat, and foraging habitat. Bird abundance was modelled separately for each guild as a function of stand variables known to be good surrogates of stand density (stand density, quadratic mean diameter, shrub cover) and maturity (dominant height, cavities). For this purpose, we used likelihood methods, which provided flexibility in the shape of the expected responses. For most bird guilds, unmanaged forests showed similar bird abundance to managed forests. Total bird abundance was maximum after regeneration cuts, due to the positive response of canopy nesters and canopy foragers. The typical open stand structure after removal cuts negatively impacted forest specialists, cavity nesters and trunk foragers, but the impact was offset by the higher number of generalists, ubiquitous, ground nesters and ground foragers. General stand descriptors such as stand density, quadratic mean diameter and dominant height were the most influential variables, whereas the association of bird abundance with shrub cover and cavities was less influential and guild-specific. We show that a shelterwood system can be a suitable management tool to promote the abundance of most common bird guilds in dense, homogeneous stands, given that some key structural legacies are retained throughout the rotation and stand structure heterogeneity is promoted. By obtaining quantitative relationships between the main structural features affected by harvests and the abundance of birds, we formulate management recommendations that are valid for forests managed not only under shelterwood systems but also under other silvicultural methods.