Replacement of Norway Spruce by Douglas Fir On Different Sites In Southern Germany - Effects On Soil and Seepage Water Chemistry.

Of the main tree species in Germany, Norway spruce is supposed to be most affected by the expected climate change. Douglas fir is considered far less vulnerable and has a growth and yield potential exceeding that of Norway spruce. Thus, current forest policy and management aims to reduce the percentage of labile Norway spruce monocultures and to increase the percentage of Douglas fir (and also that of broadleaf tree species) in German forests. However, current knowledge about the – probably site-specific – ecological effects of a substitution of Norway spruce by Douglas fir is scarce. This study compares the effects of Douglas fir vs. Norway spruce, Scots pine, and European beech on soil and seepage water chemistry at 19 sites in Bavaria (S Germany).Samples taken from the forest floor and the mineral soil (depth increments 0-10cm, 10-20cm, 20-30cm, 30-50cm, 50-80cm) were analyzed for the pH value as well as for the concentrations and stocks of organic carbon, total nitrogen and exchangeable cations. Additionally, at six sites the soil seepage water at 80 cm depth was sampled monthly during one year and analyzed for pH and major anions and cations. Preliminary results indicate soil amelioration effects on poor sites caused by Douglas fir (in contrast to Scots pine). On rich sites soil properties under European beech were best, whereas Douglas fir and Norway spruce showed no sharp distinction. Furthermore, on rich sites and older stands (>40 years), Douglas fir was characterized by higher nitrate leaching than Norway spruce. Poor sites seepage water was nitrate-free, independent of tree species.