Sustainable forest management for improving soil quality | Nachhaltige waldbauliche Maßnahmen zur Verbesserung der Bodenqualität

In some Pleistocene soils, forestry practices on sustainability were started 80 years ago. On outwash plains the pine forests were changed into pine-beech forests ("Zweistufenwald"). On moraines, pine-oak-beech forests ("Dreistufenwald") were created.Litter decomposition and carbon mineralization were significantly higher in the more natural, mainly deciduous "Dreistufenwald" than in the pine forest (p≤0.01), while C/N ratio was lower (p≤0.001). Nutrient availability (K⁺, Mg⁺⁺, Ca⁺⁺, P₂O₅) increased, whereas the concentration of Al³⁺ ions was reduced to about one-third of that of the pine forest (p≤0.001). Higher values of microbial biomass were obtained from the soil of the "Dreistufenwald". The increase in microbial biomass was mainly due to higher fungal colonization. Soil respiration (µg CO₂-C/g*h), specific microbial respiration (µg CO₂-C/mg Cₘᵢc*h) and carbon mineralization (µg CO₂-C/mg Cₒᵣg*d) were significantly higher in the mixed forest during the entire investigation (p≤0.01). Furthermore, the abundance of the soil fauna increased in comparison to the coniferous forest. This observation was made concerning the macroinvertebrates (Lumbricidae) as well as the mesofauna (Enchytraeidae, Collembola, Oribatei). With respect to earthworms, the number of species and the biomass was higher for all ecotypes.In the "Zweistufenwald" on outwash plains no improved soil characteristics could be detected. Litter decomposition was even lower than in the coniferous sites (p≤0.001) and the concentration of Al³⁺ was higher (p≤0.001). In the pine-beech forest, microbial biomass and soil respiration were only slightly higher. The biomass of the soil fauna did not differ significantly (p>0.05) in most cases.Changes in decomposition rates were mainly due to the soil type and to interactions between soil and stocking (ANOVA). Both, soil and stocking influenced the microbial characteristics of the soils and the biomass of Collembola and Oribatei (p≤0.001). Differences in the abundance of Enchytraeidae depended on the soil and the interaction of soil and stocking, while the abundance of earthworms could be explained solely by the soil (p≤0.001). Analysis of covariance uncovered the significance of the soil fauna for the increase in soil respiration, specific microbial respiration and carbon mineralization.Moreover, soil fauna and soil microbes biased the C/N ratio, nutrient availability (K⁺, Mg⁺⁺, Ca⁺⁺, P₂O₅) and the concentration of Al³⁺ ions. A remarkable correlation occured between high biotic activity, increase in pH-values and decrease in concentrations of Al³⁺ ions in the more natural, mainly deciduous forest.