Woodpeckers as early indicators of forest naturalness

Abstract

The primary aim of conservation-oriented management is the maintenance and enhancement of forest structural and compositional heterogeneity, and the creation of nesting, breeding, sheltering microhabitats for forest-dwelling species. A 32 ha oak-dominated, 80-year-old, structurally and compositionally homogeneous forest stand was selected for the first complex conservation-oriented forest management in Hungary. By mimicking natural disturbances, active management actions were implemented in 20 ha area of the study site in the winter of 2015-2016. The management actions included the girdling of standing living trees, bark stripping of tree individuals, felling to create gaps in the canopy, downed woods, and high stumps. Altogether 15% of the living wood biomass was converted to deadwood in the 20 ha area. We found feeding signs of woodpeckers and nuthatches on the majority of the treated tree individuals very soon after the treatments, and observed the foraging activity of the following species: black woodpecker, great, middle and lesser spotted woodpeckers, grey-headed woodpecker, and nuthatch. Visual feeding sign survey was carried out in wintertime, one and two years following the active management actions on 150 treated tree individuals on the tree- (trunk, branch) and bark and sapwood parts (outer bark, inner bark, and sapwood) and described as a percentage. The surveyed trees represented three species and five deadwood types: wounded-, girdled-, downed tree, low and high stump. The statistical analysis unfolded the relation of the four background variables - tree species, deadwood type, tree part, bark and sapwood part -, and the two temporal replicates of the feeding activity. Our results showed that 1) woodpecker activity was primarily determined by the deadwood type and the bark and sapwood part variables, and was independent of tree species and tree part, 2) feeding activity was the highest on the outer bark, but feeding on the inner bark increased between the two surveys, 3) one year after the treatment significantly higher activity was recorded on the high and low stumps than on any other deadwood type, 4) the second survey detected very high activity on girdled trees and increased feeding on downed woods. These preliminary results show the rapid and changing nature of foraging activity of the investigated bird species after conservation-oriented management. The very quick response of woodpeckers and nuthatches suggests the potential use of these species as early indicators for increasing naturalness in temperate forests. In the framework of a running LIFE project, we intend to extend the survey to at least 20 oak-dominated pilot sites under active conservation-oriented management and monitor the foraging activity of woodpeckers over a long time period.