Dynamics of windthrow risk in different forest ecosystemsfor 21st century (SRES A1B, B1)

摘要

The probability and extent of wind damage in forest, depend not only on strength of a drivingforce itself (e.g. wind speed) but also on combinations of effecting agents and on a structure offorest stands. The damage-induced changes in forest structure strengthen or weaken the impor-tance of different windthrow relevant climatic factors at local or even regional scales and thusincrease or decrease the probability of the next damage event, creating positive or negativefeedbacks. The present study investigates the projected developments of windthrow risks indifferent forests in 21~(si)Century under conditions ofSRES scenarios A 1 B and BI (downscaledby CLM) taking into account windthrow-induced changes of forest structure. Risk assessment iscarried out for the example region of Soiling, Germany calculating water and energy balance offorest ecosystems with BROOK 90 (Federer et al. 2003) and wind loading on trees with Forest-GALES approach under assumption of horizontal homogeneity of forest stands. 85 years oldspruce and pine forests are chosen as typical stands and cambisols, podzolic cambisols as typi-cal soil types. The risks of windthrow/breaks for a certain forest stand result from daily combi-nations of soil water characteristics, wind load on trees with dynamical structure and of soiltexture. Model output is aggregated over 30-years periods and compared to "present conditions"of 1981-2010. The results show considerable increment of windthrow risks towards 2100 rela-tively to "present state" caused by weak changes in precipitation and wind patterns and strongincrease of mean air temperature, whereas the increment is higher for pine under AlB and forspruce under B1 scenario. It is shown that for Soiling the wind damage induced changes ofstructure and microclimate provide a positive feedback i.e. - increase the probability of the nextdamage event.