Effect of water level and climatic factors on the radial growth of black alder

Black alder (Alnus glutinosa (L.) Gaertn.) is a widespread tree species in Europe and the western part of the temperate climate zone. The area of forest in Latvia dominated by this tree species has substantially decreased due to wide-spread forest drainage. To predict future changes due to environmental change, it is extremely important to understand the function of ecosystems with black alder and their dynamics. Tree rings can be used as a proxy of past environmental factors. The aim of the study was to determine the effects of meteorological and hydrological factors on radial growth of black alder at two study sites (Dursupe and Raķupe) in Latvia. The response of black alder trees to the influence of climatic and hydrological factors was found to depend on site conditions, i.e. a climatic effect was observed in conditions when the water level was low. Spatial variation in the strength of the relationship of black alder growth to temperature, precipitation, and river level suggests that alder growth is more susceptible to drought stress on higher river banks, where the water table is deeper. Black alder trees growing on low river banks can potentially be used to reconstruct past water-levels.