Response of woody vegetation and soils to modern climate change in the Altai Mountains

The upper forest boundary in the mountains is a reliable bioindicator of modern climate change, though its dynamics are influenced by multiple factors. Conjugate studies on the structure of tree stands and the soil properties across the elevation gradient were performed at the treeline on slopes of different exposures in the Altai Mountains. The oldest trees on the northern slope were established in the mid-15th century, but intensive expansion began in the 20th century, whereas tree establishment on the eastern slope began later and occurred over a shorter period. A significant positive correlation was revealed between summer and winter temperatures, winter precipitation, and the rate of Pinus sibirica establishment. The open forest boundary reaches its highest elevation on the eastern slope, where conditions are intermediate between the northern and southern slopes in terms of snow cover duration and land surface temperature. The differences in soil types reflect the contrasting conditions influenced by slope exposure. The earlier colonisation of northern slopes has led to the formation of typical forest soils (Skeletic Podzols) at higher elevations under open forest stands. These soils are more acidic, with slower litter decomposition and pronounced accumulation of carbon and nutrients in their organic surface horizons, while their mineral horizons are nutrient-poor. In contrast, soil at the eastern slope (Folic Leptosols) has a higher element content throughout the soil profile and displays minimal disparities and variation in the morphology and chemistry across the treeline ecotone. The mismatch transition between vegetation and soil belts suggests that soil properties respond to climatic changes more slowly than vegetation dynamics.