Spatial-temporal vegetation succession in Yao'an County, Yunnan Province, Southwest China during 1976-2014: A case survey based on RS technology for mountains eco-engineering

The remote sense (RS) technology was adopted to explore the vegetation succession from 1976 to 2014 in Yao'an County, Yunnan Province, Southwest China. The results showed: (i) the changes in the distribution range of major vegetation types in the study area. In the 6 statistic years after 1976, in the study area, the distribution range of the secondary vegetation shrank greatly in 4 different subareas (northeast, southeast, northwest and northwest subarea), at 4 different altitudes (1500-1800 m, 1800-2100 m, 2100-2400 m and 2400-2700 m), on 4 different gradients (0-8°, 8-15°, 15-25°, 25-35°) and on 4 different aspects but the flat land (sunny slope, semi-sunny slope, semi-shadowy slope, and shadowy slope); by contrast, in the study area, the distribution range of artificial vegetation expanded greatly in all the subareas, at 2 different altitudes (1800-2100 m and 2100-2400 m), on 3 different gradients (0-8°, 8-15°, 15-25°), and on the 4 different aspects but the flat land. (ii) The increase and decrease in distribution area of major vegetation types in the study area. During the research period, the total area of major vegetation fluctuated between 1471.92 and 1196.94 km2, averaging 1255.52 km2 annually, with the fluctuation rate between −4.67% and 17.24%. In the second statistic year (1989), the total area of major vegetation decreased sharply, and then remained relatively stable afterward. During the research period, the distribution area of the secondary vegetation decreased sharply in the 6 statistic years after 1976, in contrast to the sharp increase in the distribution area of artificial vegetation in such 6 years. During the research period, the total area of major vegetation decreased by 258.73 km2 in total, among which the total area of the secondary vegetation decreased by 342.52 km2 in contrast to the increase in artificial vegetation by 83.78 km2 in total. Thus, it indicated that the secondary vegetation in the study area had been damaged seriously, and the construction of artificial vegetation lagged behind, so there was a potential danger in ecological safety, which should be concerned and precautioned.