Evaluation of the Effect of Thinning and Replanting on Succession Process of Betula spp. Natural Secondary Forests in Subalpine Regions of Western Sichuan

Survival rate of replanting, total biomass, diversity of shrub and grass layers and water conservation ability of ground cover and soil from different modes (7 modes in all, they are respectively S1+B1, meaning to do nothing; S2+B1, meaning cutting down 20% birch according to stock; S2+B2, cutting 20% birch according to stock and replanting spruce seedlings according to 2 500 trees per hectare;S2+B3, cutting down 20% birch according to stock and replanting spruce seedlings according to 2 000 trees per hectare;S3+B1, meaning cutting down 40% birch according to stock;S3+B2, means cutting down 40% birch according to stock replanting spruce seedlings according to 2 500 trees per hectare;S3+B3, cutting down 40% birch according to stock and replanting spruce seedlings according to 2 000 trees per hectare) have been measured and sampled, and Effects of thinning and replanting on Succession process have been analyzed from Betula spp. natural secondary forests through representative sampling, harvesting and modeling, evaluated by subordinate function method. The result showed that seedlings, diversity of shrub and grass under forest and the stand biomass that mainly came from tree biomass increased at different level, but not for water conservation ability of ground cover and soil after thinning and replanting 1 years later. S2+B3 mode was the best one for effecting on succession process of Betula spp. natural secondary forests in all of 7 modes.