The Effect Of Vegetation Homogenization On Soil Properties And Process

Global and regional scale climate warming caused many changes in hydrologicalprocesses in arid and semi-arid regions. The serious environment and soil erosion of the LoessPlateau, afforestation of farmland, adjustment of land use structure, conservation tillagewhich improve soil fertility, all of physical and biological measures to control soil erosionand other measures have been vigorously carry out on the Loess Plateau, meanwhile thereconstruction of artificial vegetation has profoundly changed the eco-hydrological processat regional scale, and further affect ecosystem stability. The human activities have become themost important causes of global vegetation homogenization and direct drivers.To understandthe impact of vegetation homogeneity on soil properties and dried soil layers distributionunder slope scale. A typical hill-slope was selected under different vegetation types for thestudy in2011, as well as to understand the changes of soil properties and hydrologicalprocesses under reconstruction of artificial vegetation at regional-scale. In2012-2013, carriedout an intensive soil survey and high-density study at different scales on typical LoessPlateau. A total of40soil samples were corrected from0-500cm and taken80undisturbedsoil samples of surface(0-20cm)and subsurface(20-40cm)related information at eachsampling point under slope scale. In the Loess Plateau, a total of90representative soilsamples at the depth of500cm along a typical length of900km transect did the same sampleway. All the soil samples were taken to the laboratory for measurements of soil organiccarbon, total nitrogen,N-NO3, N-NH4, pH, soil mechanical composition and bulk density,and then made the correlation analysis, the main results are as follows:(1) At hill-slope scale, The effect of vegetation homogenization on soil properties of0-20cm soil layer is not significant, and effects20-40cm soil layer obviously, it shows thedistribution pattern of the terrain and vegetation which control the pattern of soil properties,respectively, There is more excess seepage on the Loess Plateau, The effect of vegetationhomogenization is not obvious on semi-arid areas of low rainfall and urgency of the monthand on season of less precipitation of semiarid region, the role is obvious. Therefore, atadequate rainfall in semi-arid areas, changing the soil micro-topography with regional factorsthat makes natural precipitation impoundment infiltration is particularly important.(2) At hill-slope scale, The effect of vegetation homogenization makes the dried soil layers connects together, forms the dried soil layer eventually, which make difficult recovery,and further result in soil degradation, shows vegetation control their distribution pattern.While gradually reduced thickness of dried soil layer along the slope increases at erosiongully. Therefore, It is important to arrange reasonable vegetation mode, reduce the density ofvegetation. Planting vegetation of shallow tillage reduces water evaporation at the top of thehill and erosion gully.(3) On the Loess Plateau, soil organic carbon of0-20cm soil layer only account for7.2%-9.8%at the depth of500cm, It was estimated only0-20cm soil layer of soil organic carbonreserves at previous studies, which much lower than the actual practice, the potential of LoessPlateau carbon sequestration needs further study. At every point, the same aged caraganaground, with planting density increasing, the soil organic carbon density increases, whenincreases to a certain extent, which decreased gradually; different species shows differentcarbon sequestration potential, which show Ash> Apricot> jujube; the same aged appletrees, shows different soil organic carbon density with different distribution patterns, and withspacing increases.(4) The role of vegetation homogenization causes dried soil layers, especially plantinghigh-density of vegetation shows the main factors. which destroyed soil structure anddecreased soil organic matter, also could lead to further soil degradation. Meanwhilevegetation homogenization role in semiarid areas under little precipitation conditions cansignificantly improve soil water reserves..