Deadwood in Norway spruce dominated mountain forest reserves is characterized by large dimensions and advanced decomposition stages

Deadwood provides key habitats for a variety of forest species. Thereby, not only deadwood quantity, but also its quality (dimensions and decay stages) as well as its spatial distribution is of importance for the presence of specific species, but assessments of these properties are rare. We provide a comprehensive analysis of deadwood characteristics in seven Norway spruce (Picea abies) dominated natural forest reserves in Swiss mountain regions, with a particular focus on lying deadwood. On average, the reserves featured lying deadwood volumes of 80 ± 23 m³/ha (range 1–343 m³/ha), generally consisting of large dimensions and advanced decomposition stages, two features particularly important for saproxylic species. Standing deadwood volumes averaged 32 ± 23 m³/ha (range 2–124 m³/ha). These values of deadwood quantity and quality are comparable to or even higher than in other deciduous and coniferous forest reserves across Europe. With respect to the spatial distribution of deadwood, we found two patterns of tree fall: (1) wind disturbances resulted in uniformly oriented lying deadwood (i.e., logs having similar orientation), and (2) small-scale, stand-internal mortality causing rather randomly oriented logs. Traces of former management are still visible in the study plots, and the investigated forest reserves do not feature the characteristics of virgin forests yet. Nevertheless, our results are helpful to elaborate and examine biodiversity strategies with respect to targeted deadwood levels in managed forests.