Abstract: The subalpine degraded forestlands in Northwest Yunnan were categorized as five degradation stages, and the characteristics of the vegetations and soil nutrients on each type of the forestland were studied by the method of sampling plot. The results showed that on the degraded forestland with Quercus pannosa as the climax, the numbers of woody plant family, genera and species increased with the succession series from herb to shrub to tree communities, and shrub species had a particularly noticeable increase. As for the proportions of plant functional groups, annual herbs occupied larger in early stage but declined gradually along with perennial plants in middle and late stages, while shrubs and trees had an increasing trend through out all stages, being reached the greatest at needle and broadleaved mixed forest stage and then declined to some extent until steady. In different stages, soil pH had some decrease, soil organic matter, total N, hydrolysable N and available K had an increasing trend, while soil available P had no definite change pattern.

Key words: Petroleum hydrocarbon contamination, Wastewater irrigation, Paddy soil, Microbial population, Soil enzyme activity