Effects of Climate Change on the Vulnerability of Norway Spruce Stands - Soil Hydrological Contraints for Forest Management in Austria's Lowlands

Berlin

2011

S. 127-140

Artikel aus einer ZeitschriftUnselbständiges Werk

200168912

Increasing drought stress, a very probable consequence of climate change, will heavily affect spruce dominated low elevation forests. The rough classification of risk areas, based on long term meteorological data, can provide only a hint for forest management. Local site factors and especially the soil water regime play a crucial role. Both studies highlighted the importance of the soil texture. It is well known that root system on Norway spruce is unable to penetrate heavy clay rich soil horizons (Oltchev et al. 2002). Though in drought situations a redristribution of the fine roots of Norway spruce to deeper mineral horizons can occur (Persson et al. 1995), other tree species, like birch and aspen are able to exploit deeper soil horizons more efficiently (Gartner 1997). Hence in drought stress periods these tree species can compensate the decline of available soil water by using deeper soil water reservoirs for maintaining their transpiration. Another reason for the drought stress of Norway spruce is the inefficient absorption of soil water by the fine roots due to the high negative water potential (Burk 2006). The sensitivity of Norway spruce to water stress was also shown by Ciencala et al. (1997) and Lagergren and Lindroth (2002). Also in mixed stands Norway spruce seems to be endangered by drought stress due to the belowground competition. However, it must be emphasized that there is only little information available about the belowground competition of tree roots. Therefore, the findings of the study site "Kreisbach" cannot be directly transferred to other site conditions and/or tree species. The management of spruce dominated forests in low elevation should observe the following guidelines. First of all, thel ocal site conditions should be analyzed thoroughly (site mapping). On heavy, clay rich or on dry and shallow soils the amount of spruce should be significantly reduced. Highly unstable Norway spruce stands should be converted into more stable mixed stands (Oleskog and Löf 2005; Spiecker et al. 2004). On such sites deciduous and more drought tolerant tree species, like oak and hornbeam are future forest management options (Lexer et al. 2007). After large scale disturbances in spruce monocultures on such sites the natural regeneration of pioneer tree species, like birch and trembling aspen play an important role in managing the unfavourable site conditions in the early regeneration phase. On more favourable sites, appropriate thinning strategies can help to improve the water supply in spruce forests (Laurent et al. 2003). A reduction of the rolation period might also help to lower the management risk of spruce forests.