Study on Soil Fertility Status and characteristics of Typical Degraded SecondaryForests in Subalpine Areas of Northwest Yunnan Province

【Objective】The status and distribution of soil fertility have a direct impact on the level of soil productivity and the way and direction of ecological restoration. We discussed the soil fertility status and characteristics of different degraded secondary forests which provide basic data and theoretical basis for maintaining and improving the soil productivity of vegetation restoration of degraded ecosystems in Northwest Yunnan.【Method】By using field investigation, indoor analysis and related methods, the soil pH, organic matter, total and available NPK contents of typical forest stands in Northwest Yunnan after cutting spruce and fir in 1970s, 1980s and 1990s was analyzed.【Result】The range of pH was from 4.55 to 5.46, which was acidic. With the deepening of soil depth, there was no significant change in pH value. There were significant differences among different degraded forest types and different levels of soil organic matter contents, which decreased gradually with the increase of soil depth. The content of available nutrient in soil of the same forest type decreased with the increase of soil depth, and had obvious surface aggregation, with significant differences. The contents of total N and total P in the same forest type decreased with the increase of soil depth, and there were significant differences, while there was no obvious regularity in total K in different forest types. The soil fertility factors of different degraded forest types had close correlation, which could be used to reflect the soil fertility levels comprehensively. The comprehensive scores of each degraded forest type were calculated by principal component analysis and the results showed that the comprehensive soil fertility scores of the six degraded forest types were 3.06, -2.27, -0.04, -0.13, 0.14, and -0.75, respectively, and the soil comprehensive fertility was showed as follows: degraded Alpine oakshrub ＞ degraded Betula forest ＞ degraded potaninii var. macrocarpa forest ＞ sparse Picea +Abies forest ＞ virgin Abies forest ＞ degraded Rhododendron simsii Planch shrub.【Conclusion】Different stand types had significant effects on soil fertility, and the differences in stand types led to different soil fertility conditions, among which the comprehensive soil fertility of degraded Alpine oak shrub was the best, and that of degraded R. simsii Planch shrub was the worst. Therefore, based on the soil fertility status of different types of degraded forests, a scientific system of soil fertility improvement and forest structure regulation can be established, which provides a scientific basis for the ecological restoration of the degraded secondary forest in Northwest Yunnan and the rational allocation and distribution of soil improvement.