Organic carbon pools in mountain soils - Sources of variability and predicted changes in relation to climate and land use changes

The overall impact of individual environmental factors on the content of soil organic carbon (SOC) is well known, but the simultaneous impacts of natural and anthropogenic factors on the amount and diversity of SOC pools in mountain areas are still insufficiently recognized. This study has three objectives: (1) to determine SOC pools in the mountain toposequence in relation to the climate-elevation gradient and vertical vegetation zonality, largely as a result of interference caused by human activity; (2) to predict the fluctuations of SOC pools in mountain soils affected by changes in land use/forest management and expected climate warming; and (3) to verify whether the humus form is a predictor of SOC pools in mountain soil. A spatial, climate-/altitude-dependent trend of SOC pools is clearly marked on the northern slopes of the Karkonosze Mountains, SW Poland. These SOC pools gradually increase up to the altitude of ca. 1000 m a.s.l. and then decrease in the uppermost forest and subalpine zones. The SOC pools are also strongly related to land use/vegetation (arable soils < grasslands = European beech stands < Norway spruce stands) and soil type (Luvisols < Cambisols < Podzols). Humus forms reflect the differences in SOC pools (mull < moder < mor), but the recent European classification does not clearly allocate semiterrestrial sub-types among mor and moder humus forms. Expected climate warming and present changes in land use and forest management lead to similar changes in SOC pools. However, replacing spruce monocultures with mixed or broadleaf stands reduces the SOC pools in the lower forest zones, while the timberline rise and the succession of Norway spruce on grasslands increases SOC pools in the upper forest and subalpine zones. Thus, the balance of SOC pools caused by changes in land use and climate warming will be specific in particular mountain areas, depending on their maximum altitude and existing vegetation zones, the degree of anthropogenic transformation of ecosystems, and the resilience of ecosystems to climate changes. It is expected that the SOC pools in the Karkonosze Mts and similar medium-elevation mountain ranges of Central Europe will decrease due to the larger scale of phenomena which decrease SOC pools.