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oth space and time. Land use may further complicate such analysis as recognized by Hébrard et al. (2006). This study addresses the current weakness in understanding by quantifying, at high resolution, the spatio-temporal variability of soil moisture and various controlling factors on plots receiving different grazing intensities in the Inner Mongolia grassland. A combined grid and nested sampling was conducted on five plots, ranging from heavy grazing to restored ungrazed grassland, from 2004 to 2006. The objectives of this study were (i) to quantify the spatio-temporal variability of topsoil moisture as affected by grazing intensity, (ii) to ascertain the main factors controlling soil moisture patterns, and (iii) to explore the multiple spatial scale of controlling factors by multivariate and geostatistical approaches. Understanding the spatio-temporal variability of soil moisture and its controlling factors under different grazing intensities provides valuable information for hydrological modeling, plant establishment and the environmental impacts of different land management practices in the highly degraded and sensitive Inner Mongolia grassland. Moreover, the research has generic application to the overall understanding of how land use influences soil moisture patterns over space and time. 2. Materials and methods 2.1. Field descriptions and measurements Fieldwork was conducted at the long-term experimental sites in the Xilin River Catchment, which are managed by the Inner Mongolia Grassland Ecosystem Research Station (IMGERS; 43 o 37′50′′N, 116 o 42′18′′E). A detailed description of the study area can be found in Bai et al. (2004). The vegetation was dominated by perennial grasses, e.g. Leymus chinensis and Stipa grandis. The harsh local climate limited the growing season from May to September. For the last two decades, the mean annual air temperature was 0.7°C, and the mean annual precipitation was 343 mm, of which more than 85% fell during the growing season. The soils are Calcic Chernozems according to IUSS Working Group (2006). Five different levels of sheep grazing intensity were sampled (Fig. 1): (1) 24 42
Chapter 3 Spatio-temporal variability of soil moisture in grazed steppe areas investigated by geostatistics ha area ungrazed since 1979 (UG 79); (2) 35 ha area ungrazed since 1999 (UG 99); (3) 40 ha area winter grazed only, with 0.5 sheep units (ewe and lamb) ha -1 yr -1 (WG); (4) 250 ha area continuously grazed, with 1.2 sheep units ha -1 yr -1 (CG); and (5) 100 ha area heavily grazed, with 2.0 sheep units ha -1 yr -1 (HG). The plots were adjacent to each other, apart from HG, which was 2.5 km away but on similar soils and topography. Prior to 1979, all plots were grazed at low grazing intensity. All plots except UG 79 were grazed at moderate grazing intensity from 1979 to 1999 and fenced in 1999. Fig. 3.1. Location of the sampling plots delineated as: UG 79: ungrazed since 1979, UG 99: ungrazed since 1999, WG: winter grazed, CG: continuous grazed, and HG: heavily grazed. Each plot has an area of 105 m×135 m. Sampling points were spaced at 15 m with a subgrid spacing of 5 m (the orthogonal boxes with dash line in WG and CG). Two larger geostatistical grids in WG and CG had an area of 300 m×550 m with a grid spacing of 50 m and a subgrid spacing of 10 m. Measurements in each plot were arranged on a rectangular sampling grid, consisting of 100 points with a grid spacing of 15 m and an enclosed subgrid spacing of 5 m (Fig. 1). Volumetric soil water content (0-6 cm) was measured both weekly and after rainfall events exceeding 3 mm, for 3 years during the growing season, starting in 2004. These measurements used theta-probes 43
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SCHRIFTENREIHE Institut für Pflanz
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Aus dem Institut für Pflanzenernä
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I Table of contents I Table of cont
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controlling soil moisture are of pa
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Page 101 and 102: Soil water content (%) 40 30 20 10
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Chapter 5 Modeling Grazing Effects
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Chapter 6 Modeling of Coupled Water
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References Chapter 7 General discus
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8. ACKNOWLEDGMENTS Firstly I would
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Curriculum Vitae M.Sc. Ying Zhao Of
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Schriftenreihe des Instituts Neuere
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