| Based on analysis of soil physical, chemical and biological properties, soil properties and soil integrated fertility index (IFF) of different successional series of subalpine coniferous in western Sichuan were systematically studied. The results showed soil fertility degradation of subalpine coniferous forests was mainly related to decrease of soil organic matter. With increase of artificial forest age, the content of soil organic matter decreased sharply. And soil physical, chemical and biological properties of forest became worsen.From soil physical properties analysis, soil silt, clay, physical clay, aggregate degree and structure coefficient in topsoil increased with increase of artificial forest age and soil sand deceased. Soil saturated capacity, capillary capacity, total porosity and capillary porosity showed the trend of the "U" during the successional course of artificial forest, namely, they reduced on the early successional stages, after Picea reached mature forest, soil porosity recovered slowly. The content of natural water was mainly affected by capillary porosity.From soil chemical properties analysis, the content of soil organic, humus, HA, FA and HA/FA of topsoil was more than that of bottom layer. The soil organic content in the topsoil decreased with increase of artificial forest age. Because the total N and alkali-hytrolyzable N were from mineralization of soil organic matter, their content in the artificial forest decreased with the decrease of soil organic matter. Change rules of soil P and K were complex, and their content was mainly related to parent material.From soil biological properties analysis, soil bacteria, fungi, actinomycetes and total of microbes in the topsoil were higher than in the bottom layer. In microbe composition the amount of bacteria was the most, in the next place was that of fungi, and that of actinomycetes was the least. Soil amounts of microbes of lOa artificial Picea forest were the most in the topsoil, amount of bacteria and actinomycetes sharply decreased from the early Picea forest to the mature forest, and after the mature forest, amount of fungi increased slowly. Fungi had greatly effect on decomposition of litter. The activity of Soil urease, acidphosphotase and invertase weakened with increase of soil depth. Soil enzyme activity had correlativity with many soil nutrients46and was mainly affected forest micro-environment.Based on the principle of significant effect of soil fertility factors on forest growth, soil physical factors (natural water content, bulk density, total porosity, capillary porosity, Aggregate degree, coarse silt and physical clay), chemical factors (OM. total N, alkali-hytrolyzable N, total P, humus and HA/FA) and biological factors (urease, acidphosphotase, invertase and microbes) were selected as evaluation index system of soil fertility. Applying principal component analysis, soil IFI of subalpine coniferous forest was calculated. The values of soil IFI showed the order: 10a Picea forest(2.298)>bare land(1.219)>natural forest(1.062)>secondary forest(0.505)>30a Picea forest(0.174)>20a Picea forest(-0.306)>50a Picea forest(-0.715)>60a Picea forest(-0.913)>40a Picea forest(-1.542). The results showed the trend of soil IFI changes was partial "U", namely, during the course of artificial Picea succession, soil IFI decreased sharply at the initial stage, after artificial Picea reaches mature forest, soil IFI recovered slowly and reached soil IFI of natural coniferous forest finally.Based on above-mentioned analysis, the strategy and measures to prevent the soil fertility quality degradation of artificial Picea mature forest and improve the stand ecological environment were put forward, including the rational management of inter-cutting down and fostering after artificial Picea forest matured. Because conifer-hardwood forests generally contain more tree species than pure coniferous forest, and their structure also is more complex, forestation in subalpine of western Sichuan should be conifer-hardwood forests.
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