关键词: 凋落物分解, 生态过程, 土壤氮循环, 季节性雪被, 全球气候变化

Abstract: To study the landscape spatial change of smallscale natural watersheds integrated by plateau lakes and its impacts on landscape ecological risk, Landsat remote sensing image interpretation data in Erhai Lake Basin in 1995, 2005 and 2015 were used, and GIS spatial analysis technique and Fragstats 3.4 were used to calculate the landscape pattern index. Accordingly, the landscape ecological risk model was constructed, and the temporal and spatial characteristics of ecological risk and its evolution mechanism in Erhai Lake Basin were analyzed. The results showed that: (1) The area of landscape types changed obviously from 1995 to 2015 in Erhai Basin. Woodland, grassland and water landscape decreased gradually, the cultivated land and wetland decreased first and then increased, while the construction land increased significantly. (2) The quantitative analysis of landscape index in Erhai Basin showed that the landscape spatial heterogeneity decreased, and the landscape type distribution changed from centralized to scattered, and as a result, the control effect of woodland was weakened. (3) During the past 20 years, the ecological security of the watershed tended to deteriorate, the average ecological risk index changed from 0.4998 in 1995 to 0.5896 in 2015, the proportion of high ecological risk area changed from 34.0% in 1995 to 47.8% in 2015, and the distribution of high ecological risk region changed from the arc pattern along the periphery of the basin to the multicore pattern centered on the Erhai Lake. The spatial and temporal changes of the ecological risk of the basin were closely related to the evolution of land use types and human activities. Largescale tourism development and the differences in urbanrural development mechanism were important factors leading to the increase and transfer of high ecological risk area in this region.

Key words: global climate change, litter decomposition, seasonal snow-cover, soil N cycling, ecological process