Slow and fast drivers of the natural disturbance regime in Central European forest ecosystems

Abstract

Forest disturbance regimes have intensified in many parts of the world in recent decades, and are an increasing problem for managers concerned with the sustainable and continuous provisioning of forest ecosystem services. In order to address these changes an improved understanding of disturbance regimes is needed, particularly with regard to their main drivers and climate sensitivity. Here, our objectives were to first quantitatively describe the recent disturbance regime of forest ecosystems in Austria (3.99×106ha). Second, our aim was to identify the main drivers of the disturbance regime, distinguishing slow, predisposing factors and fast, inciting factors. We utilized district-level disturbance observations from 2002 to 2010, and focused on damage from wind and bark beetles, the most detrimental abiotic and biotic disturbance agents in Europe. In a two-stage approach, we first analyzed the influence of slow, predisposing variables on the spatial variation in mean disturbance damage, using principle component regression. Subsequently, the year-to-year residuals from these average damage levels were regressed against fast, inciting factors related to disturbance occurrence.Overall, this two-stage analysis explained 48.7% (wind) and 67.1% (bark beetles) of the spatio-temporal variation in disturbance damage. On average, wind and bark beetles damaged 0.26% and 0.19% of growing stock per year. The analysis of damaged forest areas suggest a mean disturbance rotation period of 746 and 365years for wind and bark beetle disturbance. Variables related to species composition were the most influential factors on the predisposition to both disturbance agents. Societal factors were found to be of similar importance as climatic variables. Overall, these predisposing (slow) variables had a stronger influence than inciting (fast) drivers, of which weather-related variables and spatio-temporal interactions within the disturbance regime were the most prominent factors.Our results indicate that important drivers of the disturbance regime can be influenced by forest management directly, but also underline that response times are likely to be slow. Furthermore, fast, inciting factors – although largely beyond the influence of management – have the potential to be used as early warning indicators of impending disturbance damage. Overall, disturbance regimes were found to be highly sensitive to both climate means and extremes, emphasizing the importance for improved risk management in forestry in the face of climate change.