Spatial Response Patterns in Biotic Reactions of Forest Trees and their Associations with Environmental Variables in Germany

Spatial patterns in biotic reactions of forest trees (secondary growth, defoliation, nutrition) in Germany and their associations with conditions and changes in forest soils and with other environmental variables were investigated. The study aimed to identify areas at risk and risk factors. Growth ring widths and defoliation indicated drought stress as main risk factor. High annual mean temperature deviations of approximately 1.5 °C from the long-term mean (1961–1990), particularly in combination with high negative precipitation deviations, were associated with increased defoliation in all four main tree species. Defoliation development types that showed clear large-scale spatial distribution patterns were identified for all species. The defoliation development types were in good accordance with the landscape regions of Germany. Weather conditions, in particular deviations of temperature and precipitation from the long-term mean, explained a large proportion of differences among defoliation development types. South-western Germany was the region at highest risk for defoliation in recent years. This finding was mainly attributed to severe drought stress in this region in the previous years. Nutrition types did not display a strong spatial pattern. In regions affected by chronic high N deposition or where intensive liming has been conducted, antagonistic effects of K with other nutrients ( NH+4 , Ca) probably played a role in frequently observed deficient nutrition of forest trees with K and also in defoliation. Mitigation of climate change should have top priority. Environmental policy and forest management should further aim to reduce stress factors originating from air pollution and nutrient deficiencies in order to facilitate the regenerative capability of forest trees and adaption to climate change.