Ecological Heterogeneity In The Sandy Grassland Of Ordos Plateau,China

Chen, Yufu Directed by Professor Dong, MingThe importance of spatial heterogeneity in ecology lies in its ubiquity as a feature of ecosystems and in the ecological effects it raises. Spatial heterogeneity has an important place in ecological theories. It is a matter that has to be dealt with in the practice of ecosystem managements and landscape planning. In this thesis, patterns and dynamics of the spatial heterogeneity of the vegetation and soil of the main landscape types, including the sandy land and wind-eroded ridge, in Ordos Plateau sandy grassland (37?8'~40?2'N, 106?7'~111?8'E), China, were quantitatively studied by means of field investigation and experiment.In the sandy land, scale-dependent spatial autocorrelations and hierarchical structures were revealed using semivariogram and fractal analysis for the vegetation cover and the number of plant species along the two 5 km transects meeting at right angle. Spatial variations of vegetation structure of the sandy land occurred mainly on fine scales, and most vegetation patches were 5-10 m in diameter. A moderate clumping of mobile sand sites where vegetation covers were less than 20% were discovered using lacunarity analysis. The relation among the vegetation cover, number of plant species, soil organic C and total N contents varied with the spatial scales and the habitats. Field investigations into the regenerations and the clonal growth of the rhizomatous grass Psammochloa villosa in the wind-eroded sandypatches showed that the existence of clonal plants was able to facilitate the stability of the wind-eroded sandy patches, and that the clonal growth of plants across boundaries between patches lead the fluxes of matter and energy between the patches and consequently influence the dynamics of their spatial heterogeneity.In the wind-eroded ridge, the soil was barren and textured with middle- and fine-sands in the mid-slope, reflecting aeolian deposition at the mid-slope due to the wind-transportation activities. Accordingly, a psammophyte community dominated by Artemisia ordosica was found in the mid-slope, which was completely different from the typical steppe plant community (Stipa bungeana + Thymus serpyllum + Artemisia frigida) on the ridge top. The plant community along the hillslope was mainly controlled by environmental gradient associated with topography and therefore dominated by large-scale spatial variance.