Forest soils are an important component of the global C cycle as they store large amounts of organic carbon (OC). Particularly in mountain forest ecosystems, soil organic matter is of crucial ...importance for site productivity and ecosystem services, but probably sensitive to climate change. Robust information about the OC stocks of mountain soils is rare due to their limited accessibility and large spatial heterogeneity. Our study covered the entire German Alps in a large-scale sampling campaign in 2011 and 2012, and provides soil organic carbon (SOC) stock data obtained from 150 forest soil profiles with different site conditions (elevation, aspect, air temperature, precipitation, parent material, soil type) and different intensities of historical forest utilization. The mean SOC stock of the investigated soils is 10.9kgm−2. The median value is 9.6kgm−2, indicating a skewed distribution of SOC stocks in forest soils of the German Alps. On average, 30% of the SOC stock is bound in the organic surface (O) layer, and 70% in the mineral soil. SOC stocks show a considerable dependency on site conditions (elevation, air temperature, precipitation, parent material). Soils in the German Limestone Alps show a significant OC stock gradient from W (Werdenfels) to E (Berchtesgaden region), which probably has been caused by more intense historical forest utilization in the latter compared to the former region. Soils at high-elevation sites with low air temperature and high precipitation have particularly large OC stocks. However, the elevation and climate effect is statistically significant only for precipitation due to the large variation of other factors with relevance for SOC stocks (e.g. parent material, soil type) in a given elevation/climate stratum. Histosols on consolidated calcareous bedrock and Histic Rendzic Leptosols have significantly larger SOC stocks than Rendzic Leptosols, Rendzic Cambisols, or soils on easily-weatherable parent material (marl, clayey sandstone, moraine). The fact that SOC stocks in forest soils of the German Alps are by trend larger at high-elevation sites with low air temperature and high precipitation suggests a sensitivity to the ongoing climate change and a risk of SOC losses for the predicted climate scenarios.
•SOC stocks of forest soils in the German Alps are on average 10.9kgm−2.•Highly skewed distribution; majority of soils have SOC stocks <8kgm−2.•Less SOC in Eastern German Alps, where historical forest utilization was intensive.•SOC stocks are dependent on site elevation, air temperature and precipitation.•SOC stocks are sensitive to the ongoing climate change.
BACKGROUND AND AIMS: For the mountain forests of the Alps, limited comprehensive information is available about soil stocks of important nutrients (N, P, K), stand nutrition, and relationships ...between soil status and stand nutrition. METHODS: We investigated total and plant-available soil N, P, and K stocks and the nutritional status of Picea abies concerning these elements on 14 forest soil monitoring sites in the Bavarian Alps. RESULTS: Mean soil N, P, and K stocks are 8.0 Mg N ha⁻¹, thereof 14 % bound in the forest floor, 1.7 Mg P ha⁻¹(2 % in forest floor), and 42 Mg K ha⁻¹(0.2 % in forest floor). Citric acid-extractable orthophosphate and exchangeable K contribute to 3 and 0.7 % of total P and K, respectively. Spruce N, P, K, and Mn nutrition differs considerably among sites, with Rendzic Lithosols being most critical, whereas trees on deeply weathered soils are well supplied. CONCLUSIONS: According to our estimation, the forest is characterized by an insufficient supply with N, P, and/or K at about 30, 20 and 10 % of the forest area in the Bavarian Alps, respectively. A large part of the Bavarian Alps can be judged critical and prone to nutrient shortage in the course of humus degradation and associated SOM losses.
•First assessment of soil OC and N stocks under primeval forest in the Bavarian Alps.•Significant loss of forest floor OC (−78%) and N (−77%) under managed forest.•Significant loss of total topsoil ...OC stocks (−47%) under managed forest.
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.
Forest soils store large stocks of soil organic matter (SOM) and are of vital importance for the ecosystem supply with nutrients and water. According to the available literature, depending on ...management regime and site properties, different negative and positive effects of forest management (particularly of forest thinnings and shelterwood cuttings) on soil organic carbon (SOC) and nitrogen (N) stocks are observed. To elucidate the long-term impact of different shelterwood systems and small clear-cuttings on the OC and N stocks of shallow calcareous soils in the Bavarian Alps, we conducted soil humus inventories on different plots of a mixed mountain forest management experiment started in 1976. The silvicultural multi-treatment experiment consists of a NW-exposed Main Experiment (ME) site with eight plots of different cutting intensity (two unthinned controls, two light shelterwood cuttings = 30 % of basal tree area removed, two heavy shelterwood cuttings = 50 % removed, and two clear-cuttings = 100 % removed) on Triassic dolostone. Additionally, plots were installed at a N-exposed dolostone (ND) site and two sites (FL, FH) on Flysch sandstone (each with one unthinned control and one heavy shelterwood cutting). The shelterwood cuttings from 1976 were repeated in 2003 to re-establish the overstorey basal area as produced by the first cutting in the different plots. Thirty-five years after the first treatments, forest floor SOC and N stocks were significantly decreased (up to −70 %) at the different shelterwood and clear-cut treatments compared to the unthinned control at the ME site despite vigorous development of natural rejuvenation. Also significantly smaller topsoil (forest floor plus mineral soil 0–10 cm depth) OC stocks (between −16 and −20 %) were detected at the thinned compared to the control plots. Differences in topsoil N stocks were also considerable (between −3 and −14 %), but substantially smaller than OC stock changes. For the total soil down to 30 cm depth, OC stocks in the differently thinned plots were consistently smaller compared to the unthinned control plots. Comparable to our findings at the ME site, heavy shelterwood plots at the three other sites (ND, FL, and FH) showed significant losses of OC in the forest floor (up to 43 %), mineral soil (up to 38 %), topsoil (up to 38 %), and total soil (up to 34 %). Significant large absolute and relative SOC decreases coincided with sites characterized by large initial humus stocks. Moreover, significant effects of heavy shelterwood cuttings on SOC and N stocks (on average 23 % SOC loss and 13 % soil N loss for the forest floor plus the uppermost 10 cm mineral soil) were detected on a regional level. Our results show that different shelterwood systems are accompanied with a considerable long-term decrease in OC and N stocks in shallow calcareous forest soils of the Bavarian Alps. However, a comparison with a windthrown forest stand at a nearby similar site indicates that SOM losses after thinning operations are small compared to decreases following windthrow or other calamities with subsequent large soil erosion and increased mineralization processes.
München, Technische Universität München, Diss., 2015
Munich, Technical University of Munich, Diss., 2015
München, Technische Universität München, Diss., 2015
