Habitat selection of an old-growth forest specialist in managed forests

Abstract

Old-growth specialists are among the species that are affected the most by commercial forestry, and as a result, many of these species are in decline. Knowing their habitat requirements is crucial for their effective conservation. The white-backed woodpecker (Dendrocopos leucotos) is one such species that is negatively affected by intensive forest management. Because the species is highly dependent on the availability of high amounts of dead wood, it typically occurs in primeval forests. As a consequence, it has become a victim of habitat loss in several European countries. We investigated habitat selection of the white-backed woodpecker in Western Austria, Eastern Switzerland and Liechtenstein. Here, most forests are managed. This raises the question which factors enable the occurrence of an old-growth forest habitat specialist in a landscape with forests which are predominantly managed. The aim of this study was to reveal patterns in habitat selection of the white-backed woodpecker in order to develop measures for the conservation of the species. We recorded presence/absence of the species in 62 1 km2 plots in 2015 and 2016 with two within-season replicate surveys in each year, as well as habitat structure. We used dynamic site-occupancy models to compare a priori expectations on relationships between occupancy probability and habitat covariates. Each model was run at two spatial scales to find out whether white-backed woodpecker occurrence is better explained by habitat structure over a large area (1 km2) or by habitat composition of small patches rich in dead wood (0.25 km2). Occupancy probability was best explained by covariates describing forest structure: it was positively correlated with the average diameter at breast height of live trees, the number of live trees with dead branches, the proportion of deciduous trees, and the area covered with forest within the plots. The analyses at different spatial scales indicated that small patches with high amounts of dead wood containing these factors are sufficient for the occurrence of white-backed woodpeckers in the study area. Altogether, forest management in white-backed woodpecker habitats is possible, but should not be done intensively. Patches with old deciduous forests and high quantities of dead wood should be retained or created to enhance habitat quality for this species.