Recent Organic Matter Losses of Mountain Forest Soils in the German Alps Are Likely Caused By Climate Change.

Soil organic carbon (SOC) in high-latitude or mountain forest ecosystems is sensitive to climate change. According to the result of altitude gradient analysis, current climate warming is supposed to induce SOC losses in mountain forest soils, resulting in reduced soil fertility, ecosystem service provision, and positive feedback to climate change. Here we show for the first time by direct measurements that topsoil organic carbon (OC) stocks of mountain forest soils in the German Alps have decreased markedly (on average by about 14%) during the recent three decades, which were characterized by a significantly increasing summer half-year air temperature. Absolute and percentage SOC stock decreases were largest for forest soils with large OC stocks, whereas forest soils with small topsoil OC stocks (<8 kg OC m-2) as well as soils under meadows with extensive mountain pasture did not show a decrease. Low-elevation forests at sites with higher mean annual air temperature (MAT) showed larger SOC losses than high-elevation forests with lower MAT.