Tree microhabitat abundance and richness in Central European montane forests as indicators for future old growth elements

Abstract

The continued provision of old-growth elements in forest landscapes has been identified as a critical factor for biodiversity conservation in Central Europe. A well-established method of estimating the potential of forests to maintain biodiversity is to quantify tree microhabitat structures. Our aim is to predict the microhabitat abundance and richness for collectives of potential habitat trees (15 largest trees per plot). Microhabitats were inventoried on 2085 trees across 139 plots (each 1 ha) and assessed based on a detailed catalogue comprising 64 different microhabitat structures in montane forests of the Black Forest, southwest Germany. We tested the influence of forest management, forest cover in surrounding landscape, forest type, structural complexity (number of standing dead trees), altitude and average tree size on the abundance and richness of microhabitats on living trees. Generalized linear models (GLM) were used to identify the significant drivers of abundance and richness of microhabitats. The results indicate that the abundance of microhabitats of the respective 15 trees is greater on plots located in higher altitudes. Increasing average tree diameter leads to significantly higher abundances and richness of microhabitats. The collectives of inventoried trees located in monospecific coniferous forests have the highest abundance but those in mixed-coniferous-broadleaved forests have the greatest richness of tree microhabitats. Additionally we explored to which degree specific microhabitat types are influenced by the forest variables. The occurrences of 11 out of 64 specific microhabitat structures show a relation to forest management, forest type, altitude or average tree diameter. Specific microhabitats are increasing in mixed-coniferous-broadleaved and in relation to average tree size. The altitude influences especially abundances of epiphytes on potential habitat trees.This study demonstrates that based on the selected forest attributes the average abundance and richness of microhabitats can be reasonably well predicted and the occurrence of specific microhabitats can be identified.