Auswirkungen des Extremhochwassers 1999 auf die Flächendynamik und Bestandsstruktur der Uferröhrichte des Bodensees

Abstract

In consequence of the extreme flood at Lake Constance in 1999 the reed belts showed a severe loss in vitality so that a permanent damage could be expected. The monitoring project presented here focuses the documentation of the damage following the disturbance event, the identification of co-factors, and is designed to find out significant stressors that may impede the recovery of the reeds. The monitoring is based on CIR aerial photo interpretation, quantitative GIS-analyses and field data. The design of the study implies the definition of five degrees of damage using the interpretation of CIR aerial photo series from July 2000. The aquatic reed beds were digitised and areal sums were calculated. These data were compared with the corresponding data from 1999 and 1993. Stand structural and biomass attributes were investigated in 50 randomly distributed permanent plots covering all site types and damage degrees. The results showed a loss of about 24 hectares of aquatic reeds at Lake Constance Untersee alone. The stands which had survived showed a great patchiness in terms of culm density, shoot population composition, culm architecture, and aboveground biomass production. Severely damaged stands were mainly composed of secondary shoots, whereas primary and insect infested shoots dominated in less damaged stands. One co-factor which explained the patchiness was the vertical position of the stand, i.e. the probability of being severely damaged increased with increasing distance below mean water level. The monitoring programme will be continued till 2003.