Altitudinal Distribution Rule of Betula platyphylla Forest's Soil Organic Carbon Density And Its Influencing Factors in Xiaowutai Mountain in Hebei
The natural forest of Betula platyphylla, which is widely distributed in northern China, is important ecological protection and commercial timber species. In global warming, studying the distributional law of soil organic carbon density (SOCD) along the altitudinal gradient and its influencing factors in Betula platyphylla forest will be very important for illuminating the formation mechanism of forest soil organic carbon and reasonable evaluation of forest carbon storage in this region. The Betula platyphylla forest were located in Xiaowutai Mountain Shanjiankou (lower elevation from 1 400 m above sea level to 2 000 m at its upper limit). The slope, aspect and the stand types were consistent. This study set a series of plots and samples along an altitudinal gradient on Betula platyphylla forest. It tested soil organic carbon content at different attitudes in order to discusse the distributional law of soil organic carbon density (SOCD) along the altitudinal gradient. Based on that, grey relational analysis was used to analyse the impacts of hydrothermal ration, biomass, litter storage, soil bulk density and soil total nitrogen on this law. The results showed that, SOCD presented a decreasing trend with increasing soil depth; at a depth of 0~20 cm SOCD accounted for about 50% of the whole section. From the lower elevation limit to the upper limit, SOCD presented an significant change which increased first and then decreased, the peak appeared at the altitude of 1 550~1 700 m, it was about 12.03 kg·m~(-2). The grey relational degree values of hydrothermal factors, vegetation factors, soil factors and SOCD showed that biomass, litter storage and soil total nitrogen were main regulating factors of the spatial variability of SOCD along the elevation. The variation of SOCD along the elevation results from the combined action of hydrothermal gradient variation and affected vegetation and soil factors.