Studies On Soil Anti-erosion Under Different Forest Vegetation

Through a large number of field investigations and laboratory testing, The capability of soil anti-erosion and the quantitative relationship among various factors under the different forest vegetation were studied systematically in Sino-America Forest Health Projects of Majiang county, Guizhou Province. The effect of the litter, slope, rainfall in forest and surface runoff on soil anti-scourability was discussed, and the relationship between the content of soil organic matter and aggregates and soil corrosion resistance under different vegetation was analysed. The root system role on the soil moist conservation and anti-erosion under the different age forest of Pinus massoniana was analysed too, The object of the research was to provide a scientific basis for soil and water conservation forest eco-efficiency rating in project areas.The results showed that soil erosion quantity increased with the slope, rainfall in forest and surface runoff increment, and surface runoff had biggest influence on soil anti-scourability. With the increase of age of Pinus massoniana forest, soil anti-scouribility was enhanced gradually. While on the same age of the forest, soil anti-scouribility of broad leaved forest or mixed broadleaf-conifer forest was better than that of Pinus massoniana forest, but the litter of pine needles closely packed under Pinus massoniana forest made up for a deficiency of surface soil anti-scouribility.The soil anti-scourability in Pinus massoniana young forest was lower slightly than in broad-leaved forest under slope 15°, but it declined severely when slope was above 15°. At the slope of 10°, 15°, 25°, the soil loss in Pinus massoniana young forest increased by 10.4%, 30.4%, 36.5% than in broad-leaved forest respectively; the soil loss in Pinus massoniana half mature forest increased by 24.9%, 23.7%, 33.9% than in mixed broadleaf-conifer forest respectively.At the rainfall of 10mm, 20mm, 30mm, 40mm in the forest, the soil loss in mixed broadleaf-conifer forest reduced by 0.1680g/cm~2 , 0.0901 g/cm~2 , 0.0886 g/cm~2 , 0.0611 g/cm~2 than in Pinus massoniana half mature forest respectively. When rainfall in forest was above 30mm, the soil loss in broad-leaved forest increased slowly, and the soil loss in Pinus massoniana young forest still maintained a relatively high growth momentum, which indicated that soil in broad -leaved forest was more resistant to soil anti-scourability than in Pinus massoniana young forest.At the soil surface runoff >10ml/s, the soil loss in Pinus massoniana half mature forest was greater than in mixed broadleaf-conifer forest obviously. When soil surface runoff increased to 15ml/s, 20ml/s, the soil loss in Pinus massoniana half mature forest was 2.40 times, 2.74 times respectively in mixed broadleaf-conifer forest. So, in the same age forest, the soil anti-scourability in Pinus massoniana forest was not as good as other forest vegetations.Forest litter can not only conserve water, block runoff, increase infiltration, but also can reduce the rain splash erosion under forest soil, head off mud, and increase the content of soil organic matter and bigger aggregates after the litter was decayed. Therefore, forest litter played a very important role in enhancing soil anti-erosion.With the increment of forest age, soil organic matter and large aggregates(> 2mm) showed the same increasing trend, the interactions among root-soil-microorganism promoted the organic matter content and the formation of large aggregates, which were beneficial to enhance the soil anti-erosion. The increment of soil organic matter and large aggregates also promoted the decrease of soil bulk density and the increment of soil porosity, thereby increased soil store water capacity and reduced soil loss. Plant roots in the soil of the interludes and intertwist promoted the formation of large aggregates, root exudates not only increased soil organic matter content, but also amended soil porosity, so root growth was propitious to improve the physical and chemical properties of soil. Fine roots (Diameter< 1mm) played an important role on soil anti-erosion. With the increment of forest age, root length, surface area and weight increased gradually. Enhancement effect of soil anti-scourability increased several times when the length or surface area of fine roots was double.The studies of forest vegetation promoting enhancement effetc of soil anti-erosion in the project area showed that the different forest vegetations can reduce 1469755t soil loss each year approximately. The economic benefits brought by forest vegetation was very significant, which supplied reference for ecological benefits charging for the currency in the project area.