Abstract: Based on the measurements of canopy interception, litter water-holding capacity and soil water storage of different stands in the Erdaoqiao watershed of upper Nenjiang River, the optimal disposition of water conservation forests in this watershed was approached by the method of an-alytical hierarchy process (AHP). The results showed that in this watershed, the optimal vegetation structure should be 24.86% of natural birch forest, 16.30% of natural Dahurian birch forest, 44.49% of natural broadleaved mixed forest, 10.88% of larch plantation,and 3.47% of grassland. After optimization, the water conservation capacity of the watershed could be improved obviously, with soil available and maximum moisture contents increased by 33.05% and 27.78%, respectively.

Key words: Taihu Lake, Non-point sources pollution, Phosphorus, Quantification