Disentangling the Impact of Forest Management Intensity Components on Soil Biological Processes

Temperate forests cover 25% of the world's forest area and most of them are managed for timber production. To increase yields, native deciduous trees have been commonly replaced by fast-growing conifers, especially in Western and Central Europe. Despite the importance of forest soils for a variety of ecosystem functions, the effects of forest management intensity on soil biological processes have not yet been sufficiently understood. Using a standardized sampling protocol that covers 200 plots across four regions with different abiotic site conditions, our study aims at disentangling the effects of individual components of forest management intensity such as (i) share of native deciduous trees, (ii) timber harvesting volume, and (iii) natural deadwood volume on soil biological processes. Our findings indicate that the effects of management practices on soil biological processes are as important as abiotic factors, such as subsoil pH value and soil texture. Piecewise structural equation modeling revealed that forest management has both direct and indirect effects on soil biological processes via humus form and topsoil pH. Generally, the ratio of deciduous and coniferous trees had the most significant effect on nutrient cycling and soil properties, followed by nutrient extraction through timber harvesting and natural deadwood volume. The strength of the observed effects was modified by regional variations in climate, topography, and bedrock. Our findings underline the high diagnostic value of humus form as an indicator of biological processes in mineral topsoil (particularly pH, C/N, and microbial characteristics can be predicted) that can guide forest managers in evaluating soil quality and identifying management impacts.