天然杨桦林密度效应的研究

Management Density Effects of Poplar and Birch Natural Forests

选择不同的林分类型和立地条件,按不同经营密度分别设立固定标准地,对天然杨桦林林分生长性状(树高、胸径、材积等)、形质指标(冠长、冠宽等)、光能利用、养分及林内土壤水分变化等进行连续的定位观测。在立地分类基础上,定量分析了经营密度对林分干物质积累量、养分归还量、林地土壤含水量、林分生长及出材量的效应。结果表明:经营密度对林分生长、干物质积累、枯枝落叶分解和土壤结构的改善具有较大影响。天然杨桦林单株叶量随经营密度增大而减少,单株叶片总面积、林分平均冠长、冠幅则以中等经营密度最大;凋落物分解率随密度增大而减少,营养元素归还量以中等经营密度为最大;密度相同,不同土层深度的土壤含水量均随土层深度增加而减少,同一土层深度的土壤含水量随经营密度减少而降低;山杨林和白桦林单位面积胸径年生长量随经营密度的增加而减少;林分蓄积以中等经营密度最大。

Rational management density was one of the key techniques to realize directive breeding of poplar and brich natural forests, which help to improve the stability and economic benefit of forests. In order to discuss the effects of different management density on the growth, fixed sample plots were set up respectively with the different density under the different stand types and site conditions. The characters （height, diameter, volume and etc）, form quality index, utility rate of luminous energy, nutrient and the moisture change of the soil were observed continuously. On the base of site classification of poplar and brich natural forests, we analyzed quantitatively the effects of different management density on utility rate of luminous energy, content of nutrition return, content of containing water of woodland soil, growth of the forest as well as the effect of timber quantity. The result showed that the management density obviously affected the growth of forests, accumulating of dry matter, litter fall decomposing, and the improvement of soil structure. The individual leaf content reduced along with the management density increasing. The total area of individual leaf and average crown of stand were maximal in the medium management density. The decomposing rate of litter fall decreased along with the density increasing. The returns of nutritive element were the most in medium management density. The moisture content of different depth soil reduced along with the depth deepening in the same density. The moisture reduced along with the density descending in the same depth. The annual growth of diameter of unit area increased along with the density descending of the polar and brich forests. The stand accumulation was the most in the medium management density.