Soil properties at the tree limits of Picea schrenkiana forests in response to varying environmental conditions on the northern slope of Tianshan mountains
Abstract:Coniferous forests consisting predominantly of Picea schrenkiana occur continuously, forming an unbroken, 1000 km forest zone extending from west to east on the northern slope of Tianshan mountains where conditions such as precipitation, temperature and terrain vary greatly. To gain insights into the role of pedological process in controlling the growth of P. schrenkiana, soil under the forests was studied along 4 transects located at Jinghe, Manasi, Fukang and Balikun where the natural conditions are typical and, therefore, representative for western, central and eastern Tianshan mountains. On the transects, soil samples were taken in the area near the upper and lower tree limits of the forest zone. The continuous distribution of P. schrenkiana on the northern slope of Tianshan mountains is a result of combined water-heat conditions and pedological factors. At the upper and lower tree limits where difference exists in soil parent material, precipitation, topography, combined water-heat conditions and local atmospheric pattern, the soil properties show a close relationship with the local conditions. Because of the presence of high precipitation over the Manasi transect, the soil is fertile and low in CaCO3 content. In contrast, low soil fertility with high CaCO3 is seen in the soil on the Jinghe and Balikun transects where low precipitation exists. Although soil properties vary spatially due to the presence of different environmental conditions across the 1000 km forest zone on the northern slope of Tianshan mountains, soil is suitable for P. schrenkiana to grow. This study indicates that soil plays an important role in controlling the continuous distribution of the P. schrenkiana forests on the northern slope of Tianshan mountains.