Customary selective harvesting has considerably decreased organic carbon and nitrogen stocks in forest soils of the Bavarian Limestone Alps

Forest soils represent an important part of the global C cycle as they store large amounts of organic carbon (OC). With its great importance for nutrient and water supply, soil organic matter (SOM) is a key site characteristic particularly in shallow mountain soils. We conducted soil humus inventories in three research areas in the Bavarian Limestone Alps to investigate long-term effects of historical forest management with selective harvesting on shallow calcareous mountain forest soils. In each research area, SOM stocks under unmanaged forest at remote sites representing the virgin forest status and those of nearby selectively harvested forest stands (repeated single tree extraction, shelterwood harvesting) with identical site factors were compared in a paired-plot approach. At each site, five soil profiles were investigated; additionally O layer thickness was measured as well as important stand characteristics were assessed at 30 points of an orthogonal grid net that had been established in each stand. OC and N stocks in the forest floor and in the mineral soil were calculated by horizon as well as by depth increment and evaluated statistically. On average, forest floor OC and N stocks were reduced by about 80% under managed forest (OC stock 25±34Mgha^-1; N stock 1.0±1.5Mgha^-1) compared to nearby unmanaged forest (OC stock 114±123Mgha^-1; N stock 4.5±5.1Mgha^-1). OC and N stocks in the mineral topsoil (0-30cm) were larger under managed (OC stock 65±22Mgha^-1; N stock 4.4±1.4Mgha^-1) compared to unmanaged stands (OC stock 55±38Mgha^-1; N stock 3.6±2.8Mgha^-1). Total topsoil (forest floor+mineral topsoil) OC and N stocks under managed forest (OC stock 89±36Mgha^-1; N stock 5.4±1.6Mgha^-1) exhibited significant OC losses of 47% and N losses of 33% compared to nearby unmanaged forest (OC stock 169±96Mgha^-1; N stock 8.1±3.4Mgha^-1). Hence we conclude that standard forest management as practiced since ca. 200years has considerably reduced SOM stocks on shallow calcareous mountain forest soils in the Bavarian Limestone Alps.