Heat and Aridity of Summer 2003 - Effects on Availability of Soil Water to the Forest

2003

S. 56

Artikel aus einem Buch

200107818

The Federal Office and Research Centre for Forests (BFW) runs several measuring stations for water budget studies in Austria. In the regions of Gradenbach (Carinthia) and Fürstenfeld (Styria two measuring stations each were selected to document deviations from the long term average of meteorological parameters such as precipitation and temperature. The precipitation sum line of the measuring station of Gradenbach in August 2003 shows a deficit of 161,7 mm (minus 83 %). At the same measuring station, in June, a maximum deviation from the monthly average temperature of + 4,6°C has been recorded. Due to the low rainfall and the unusually high temperatures of the year 2003 less water has been available for vegetation. According to measurements in the watershed of the Gradenbach groundwater tables have dropped by several meters. It is proved by sap flow measurements on birch and spruce stands near Fürstenfeld that long lasting drought stress has an influence on the natural vegetation. There has not bee enough accessible water in the soil layers to cover the increased demand of water induced by the high temperatures. Accordingly, the trees had to reduce their transpiration rate. The sap flow has dropped significantly in both tree species by the end of August. It is evident that spruce is more affected than birch by this stress phenomenon which also increases the vulnerability of trees to insect pests. The increased occurrence in the future of such extreme weather events (keyword: climate change) will lead to long-lasting damages in the forests of Austria. The risk is particularly high for stands which are not adapted to the site. Forest management plans will have to take into account this fact in the future.