Welche Faktoren bestimmen den Erfolg der Moderholzverjüngung im Fichtenurwald Scatlè?

Harsh environmental conditions in subalpine forests render Norway spruce regeneration difficult, limiting germination and establishment to a few microsites such as decaying logs. In 2002, spruce regeneration was studied on coarse woody debris (CWD) in the Swiss virgin forest Scatlè. In 2012, regeneration status and the factors characterizing environmental conditions were re-assessed. The statistical model that had been parameterized with the 2002 data also performed well with the explanatory variables measured in 2012, indicating that regeneration on CWD is a non-random, complex process resulting from the interaction of several ecological factors. A 5.5-fold increase of regeneration density was observed over the past ten years, which is most likely attributable to a higher abundance of suitable microsites on CWD: 1) an increase of moderately and strongly decayed wood, 2) average sunshine duration in June of 50 to 120 minutes per day, 3) a decrease of the plot-to-ground distance with little competition by the surrounding ground vegetation, 4) an increase of the thickness of moss cover. The mast years of 2009 and 2011 certainly were influential for the increase of regeneration density. Establishment of regeneration may start as early as six years after tree death, but logs older than 23 years were most suitable. Natural regeneration on rotten wood thus is a slow and long-lasting process, and the sustainability of regeneration requires a continuous supply of dead wood of different decay stages. Besides the important role of dead and dying trees for spruce regeneration, we also found an important role of CWD for biodiversity, as fifteen species of decay fungi were detected, two of them having the status of endangered species.