Density Effect On Natural Birch Forest

The 20 years' old natural birch density experiment forest of Dong Fanghong Forest Yard of Dailing Forest Bureau in Xiaoxing'an Mountain was selected as researching target. Standard site investigation, sampling and measurement methods were applied for researching the influence of four slope directions (east, south, west and north) and five kinds of management stand density(0.4,0.5,0.6,0.7,0.8) on forest growth, photosynthetic capacity, soil fertility and the under-story vegetation diversity. The results showed that:(1)Different management stand densities have significant influence on the forest growth. Where the average diameter at brest height(DBH)and single timber volume of individual' plant decrease with the increasing of stand density; stand volume decrease with the decreasing of stand density. The growth of forest will decrease significantly when the forest canopy density above 0.6.(2)Different management stand densities have significant influence on the forest photosynthesis.The overall performance of maximum forest photosynthetic speed, light compensation point, light saturation point, carboxylation efficiency and water use efficiency show that which will decrease with the increasing of stand density except for the canopy density is 0.7.The biological photosynthetic indexes are relatively higher under the condition that canopy density ranges from 0.5 and 0.7.(3) Different management stand densities of natural birch have significant influence on the nutrient contents of under-story soil, which shows that soil moisture content, PH value, organic matters, total N, effective N, effective P and available K will increase first and decrease later with the increasing of stand density. Among the five stand densities, the soil nutrients content is relatively higher when canopy density is 0.5,0.6 and 0.7.(4) Different management stand densities of natural birch have significant influence on the biological diversity of under-story vegetation. Among the five stand densities, the biological diversity of under-story vegetation is relative higher when the canopy density of natural birch is 0.7.