Study On Selective Cutting Intensity And Cycle Of Natural Forest

This paper has 12 pieces of natural spruce-fir forest as the object of the research, which are located in Jingouling forest farm in Wangqing forestry bureau, Jilin Province. In order to make more reasonable selective cutting intensity and cutting cycle for the sustainable management of natural spruce-fir forest, the dynamic change of the growth of primary coniferous species (which are korean pine,spruce and fir) in stand and tree layers and the diameter and volume structure of stand, the stand spatial structure and the dynamic response of the tree species structure and species diversity of natural spruce-fir forest to different selective cutting intensity has been operated. The selective cutting cycle of natural spruce-fir forest is determined based on the reasonable selective cutting intensity.This study selects the reasonable selective cutting intensity through the following methods that are the analysis and comparison of the growth rates (which are the basal area rate and the volume growth rate) of primary coniferous species of natural spruce-fir forest in different periods (which are before and after cutting and two or six or nine years after cutting), using the Weibull distribution and the rule of q value to analyze the difference of the diameter structure of stand and the proportion of strains number and volume of large and small diameter wood in different periods, using three indexes that are the mingling degree, neighborhood comparison and uniform angle index, combing with the theory of the Cobb-Douglas production function in microeconomics, to construct the forest spatial structure production function and utilizing the storey index to analyze and compare the spatial structure characteristics of natural forests and taking advantage of the five targets which are the importance value, species richness index, Simpson diversity index, Alatalo evenness index and Simpson dominance index to research the changes of tree species in tree layer after 10 years cutting. Based on the selective cutting intensity and the growth rate dynamic equation, the rational selective cutting cycle of the natural spruce-fir forest was calculated. The results are listed as follows:(1) The growth rates of stand and tree layers of selective cutting sample plots are all greater than those of the control. The sort of the growth rates of sample plots is the follows:third tree layer> second tree layer> whole stand> first tree layer. After cutting six and nine years, the growth rates of all and the first and second tree layers of different cutting intensity plots have significance difference but that of the third tree layer has indistinctive difference. The difference of growth of the second and third tree layers of middle selective cutting intensity plots is greater than that of the control.(2) After cutting two, six and nine years, the fitting effect of the Weibull model, the determined coefficient(R-square) and the value of average absolute residual of the middle selective cutting intensity plots is the best and those of the low selective cutting intensity plots is better. The q value of the low selective cutting intensity plots has been in a normal situation and the values of the strains number and volume of large diameter wood of it are all bigger than other plots and the increase rang of the strains number and volume of large diameter wood is all improved continuously, with the increase of time.(3) The mean mingling degree of the low selective cutting intensity plots is the biggest and it is in a good mixed state; the horizontal spatial distribution of it is uniform distribution; the storey index of it is the biggest and its vertical space utilize more fully; that the forest spatial structure index is the biggest and the forest spatial structure distance is the smallest shows that the distance of its spatial structure to the ideal structure has a small gap. The value of neighborhood comparison of all plots has no significant effects and there has no differences in tree size differentiation.(4) After recovering 10 years, species diversity of selective cutting plots is restored and higher than that of before. They can basically maintain the structure of tree species and species number of the original stand. The increments of the species richness index, diversity index and evenness index of low selective cutting intensity plots are the biggest and its dominance index is the smallest. It shows that the species diversity of low selective cutting intensity plots is the biggest.(5) The static growth rate calculated by the median rule can predict the selective cutting cycle of natural spruce-fir forest to some extent. When the selective cutting intensity is 20%, the harvesting period of natural spruce-fir forest is 18～27 years.