Die klimatische Trockengrenze häufiger Baumarten hängt vom Bodennährstoffstatus ab. [The climatic drought limit of common tree species depend on soil nutrient status]

n forest ecology, there is a huge experience in the ecological amplitude of tree species, which is commonly represented in so-called ecograms. However, the ecogram axes are purely qualitatively described and scaled. In the study presented here, we try to specify the drought limit in the ecogram for the ten most abundant and economically important tree species in Germany (Norway spruce, Scots pine, silver fir, European beech, pedunculate oak, sessile oak, sycamore maple, European elm, hornbeam and common ash) using generalized regression models. We use data on the occurrence of the tree species and on the soil of about 3300 plots of the second German forest soil condition survey (BZW II), combined with data from the ICP Forests Level I program (BioDiv and BioSoil) from 13 neighboring European countries as well as climate data from WorldClim. The focus is on the question to what extent the drought limit of the tree species depends on the soil nutrient status. As a predictor of nutrient status, we chose the base saturation type (BT) already introduced in practice. The warmth factor was included as Growing Degree Days, the water balance as climatic water balance in the forest vegetation period (KWB). The drought limit could be specified for all tree species except elm and pedunculate oak. It was found that not only in known nutrient-sensitive tree species (sycamore, ash, hornbeam), the drought limit depends on the BT, but also in beech and spruce. In the case of sycamore as an example of a nutrient-sensitive species, the dry climate limit on strongly acidic soils (BT 5) is already reached at a KWB of 20 l/m2, on base-rich (BT 1 and 0) only at a KWB of –150 l/m2. In beech, too, the drought limit on acidic soils has been reached more quickly than on base-rich sites (BT 5: –40 l/m2, BT 0: –120 l/m2). In contrast, the reaction of spruce is reversed (BT 5: –50 l/m2, BT 0: 10 l/m2). For pine, sessile oak and fir, the drought limit is independent of the base type and is –230 l/m2 (Scots pine), –150 l/m2 (sessile oak) and 0 l/m2 (silver fir). The drought limit specified by BT is a helpful quantity, especially in view of climate change, as it makes it possible to better estimate the potential of the different tree species. © 2018, Schweizerischer Forstverein. All rights reserved.