Combined retention of large living and dead trees can improve provision of tree-related microhabitats in Central European montane forests

Abstract

Retention of habitat trees is a common biodiversity conservation practice in continuous cover forests of temperate Europe. Commonly, living habitat trees are selected on the basis of their tree-related microhabitats (TreMs) such as cavities or crown deadwood. Owing to the increasing frequency and intensity of climate change-related disturbances, habitat trees in particular are expected to experience increased mortality rates. This may impact the long-term provisioning of TreMs. Here, we compared the TreM occurrence on living and dead trees to investigate whether dead trees support more and other TreMs than living trees. We also hypothesized that a combination of living and dead trees results in the most diverse stand-level TreM composition. We surveyed the TreM composition of living and dead habitat trees in 133 one-hectare plots in the Black Forest region managed according to a continuous cover approach. We fitted generalized linear mixed models to identify the main predictors of TreM occurrence to predict their abundance and richness. Tree identity (as a combination of species and vitality status) and diameter were the main drivers of TreM abundance and richness, which were highest on dead Abies alba. Even though dead A. alba and Picea abies supported TreM numbers similar to those provided by large living trees, their TreM composition was significantly different. This suggests that dead trees cannot substitute the habitat functions of living habitat trees, but they can complement them to increase the overall stand-level TreM diversity, in particular through decayed, large snags.