Characteristic analysis of soil physical properties of abies georgei var. smithii virgin forest in tibet

Abies georgei var. smithii virgin forest was main distribution type in southeastern area of Tibet. By adopting the posting and typical-plot method, the physical properties of the soils inside and outside the forest was studied, through two-year observation (1999 ~ 2000) in Sejila Mountain Research Station of Forest Ecosystem. The bulk densities of layer A, layer B, and layer C soils was 0.74, 0.94, and 1.34 respectively inside forest and was 0.92, 0.99, and 1.22 respectively outside forest, which indicated that the bulk density for layer A inside forest was less than that of outside forest, while for B and C layers there existed no significant difference between inside and outside forest. By comparison of the saturated moisture capacity, capillary moisture capacity, field moisture capacity, non-capillary porosity, capillary porosity, and the total porosity of soil, and values of these factors for layer A soil inside forest were higher than that of outside forest, but those for layer B had no marked difference between inside and outside forest. With depth increasing, the soil water content decreased. It was the highest in surface layer (0~10 cm), with a maximum value of 75% inside forest and 63% outside forest, and tended to be stable below 50 cm (30%~40%). Based on change law of soil water and water absorption and utilization of plant root, the soil water utilization of Abies georgei var. smithii forest was first divided into three levels: weak utilization layer (0~10 cm), utilization layer (10~50 cm), and regulating layer (below 50 cm). The soil water content of the forest was the highest in January and February in winter and had little change in growing season. The dynamic of soil water content was divided into consumptive, accumulative, receded, and stable periods. The permeability of both layer A and layer B soils in forest were better than those of outside forest. The time for reaching the stable permeation in layer A was 10 min and 45 min respectively for inside and outside forest. The results showed that the soil physical properties inside forest were superior to that of outside forest. It also indicated that the soil physical properties would be changed obviously and evolved towards adverse directions after forest interfered or destroyed.
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