Vertical distribution of soil moisture in artificial forestsin loess region of northern Shaanxi
Wang Yu, Zhu Qingke, Zhao Weijun, Wang Lina, Ma Huan, Liang Feifan, Zhao Xingkai,Li Anyi
1. Engineering Research Center of Forestry Ecological Engineering of Ministry of Education,Beijing Forestry University,100083,Beijing,China; 2. KeyLaboratory of Tourism and Resources Environment in Colleges and Universities of Shandong Province, Taishan University, 271021, Taian,China; 3. Beijing World Hazard Preventing Tech. Co. , Ltd, 100048, Beijing, China
Abstract：Soil moisture is one of the main factors that restrict vegetation growth, vegetation restoration and stand stability on the Loess Plateau in northern Shaanxi province. It also shows obvious temporal-spatial characteristics under different land use types, to pography and geomorphology, and vegetation conditions due to the effects of rainfall, surface runoff, plant transpiration, root absorption and so on.The vertical distribution of soil moisture in artificial forests reflects the characteristics of soil water consumption and stability of forest lands. Thus, the study of soil moisture in vertical profiles is important for understanding the utilization of soil moisture in artificial forests. The aim of this study was to investigate the distribution and the hierarchical characteristics of soil moisture at the 0-180 cm layer invertical profiles. In order to analyze it,three types of typical artificial forests on the Loess Plateau innorthern Shaanxi province,namely Pinus tabulaeformis,Armeniaca sibirica and Hippophae rhamnoides,were selected as the research object. Meanwhile, waste grassland in the same stand conditions was used as a reference group. The time domain reflection (TDR) was chosen to measure the soil moisture between 0 cm and 180 cm in vertical profiles. During the period from August 2010 to June 2013, the soil moisture contents were measured 3 times in every 20 cm layer. Moreover, in each observation, the probe of TDR was rotated 120 in horizontal direction. The sequential clustering method and the variation coefficient method were combined in this study in order to classify the soil layer by moisture. Results show that the soil moisture contents of Pinus tabulaeformis and Armeniaca sibirica forests were decreased respectively by 0.0193%/cm and 0.0209% /cm with increasing soil depth (0-180 cm), while the soil moisture contents of Hippophaer hamnoides forest and waste grassland were increased with the rate of 0.0046% /cm and 0.0863% /cm, respectively. Nevertheless, the soil moisture contents of the three types of artificial forests were all less than those of waste grassland between 80 cm and 180 cm in vertical profiles.Thus, studies should pay more attention to soil moisture below the 80cm soil layer in the Loess Plateau of northern Shaanxi province and determining whether it will be absorbed by the root system of the three kinds of artificial forests. Using variation coefficient method, our observation also suggests the soil layersin 0-180 cm vertical profiles can be divided into three groups, which are quickly changing layer, active layer and subactive water layer. Moreover, the soil layers can also be divided into three groups using sequential clustering method. And the grouping result is comparatively consistent with that by variationcoefficient method and by sequential clustering method. Thus, the sequential clustering method is likelyto be reasonable when used in classification of soil layer. The result of this research would provide basic theory for selecting species in near-natural affore station.
2015, Vol. 13 
