Do admixed conifers change soil nutrient conditions of European beech stands?

Abstract

Context Establishing mixed forest stands is an option for improving soil nutrient conditions and for increasing the resilience of forest ecosystems. Aims Identify the effects on soil chemistry of spruce and Douglas fir admixed in European beech forest. Methods We analysed pure and mixed species stands in Germany. The pure stands were mature European beech (Fagus sylvatica), Douglas fir (Pseudotsuga menziesii), and Norway spruce (Picea abies). The mixtures were composed of beech with either Douglas fir or spruce. The stands were located in two regions with different soil conditions. Results Our results indicated that pure spruce stands, independent of site condition, had the lowest base saturation while beech showed the highest values. The impact of Douglas fir differed between site conditions. On sandy soils, there was higher pH and base saturation under Douglas fir than under spruce. On loamy soils, however, the pH under Douglas fir and beech was lower than under spruce. The cation stocks (Ca and Mg) on sandy soils were lower under spruce and spruce/beech stands than under Douglas fir and beech. In contrast, under loamy soil, exchangeable Ca and Mg stocks were less under beech than under spruce stands. Soil exchangeable K under mixed stands was among the highest compared to pure stands, independent of site condition. Conclusions Mixed species stands reduce soil base cation depletion compared to conifer stands. Implications Admixture of Douglas fir to European beech seems to be a more reasonable option for forest management than an admixture of spruce, since it does not negatively affect soil chemistry.