Study On Dynamic Of Stand Growth And Structure Of Spruce-Fir Mixed Forest After Selective Cutting In Changbai Mountains

In this paper, using the natural spruce-fir mixed forest as the research object, which is located in Jingouling forest farm, Wangqing forestry bureau, Jilin province, stand growth and structure dynamic of more than 20 years for tending spruce-fir forest of different selective cutting intensity (0,20%,30%, 40%) and control method plots of low intensity cutting (5%-20%) were analyzed with the data of permanent plots for longtime monitoring. The detailed study contents included stand average DBH, basal area and volume per hectare, growth percentage of DBH and volume, PAI (periodic annual increment) of volume, volume structure of diameter classes, the ratio of stand conifer to broadleaf volume and diameter structure. Comparing the stand growth discrepancy for different selective cutting management, the optimal stand structure would be obtained, which will be provide theory foundation and technical support for natural spruce-fir mixed forest management of this study area. Main conclusions of this paper were as following:(1) The spruce-fir mixed forest after selective cutting of different intensity grew faster than stand with no cutting. The growth accelerated with the intensity increasing, the growth percentage of volume reached the maximum of 8.7%, then to decline with the year after cutting. The stand volume structure and diameter structure had no significant discrepancy for 6 years after cutting. Compared with the stand of no second selective cutting, the growth percentage of stand with 2 or 3 cuttings began to increase after cutting, and then decreased in 4 to 6 years later, to next cutting. The stand diameter distribution varied from inverse J-shaped to asymmetric single or multi peak curve over the time, but could be adjusted gradually after every cutting. The volume proportion of large diameter class would increase after heavy cutting, but imperial diameter class raised less.(2) Comparing tending spruce-fir mixed forest, the growth and structure maintaining of stand for control method management of low intensity cutting for many times, showed some advantages. The cutting with the intensity between 15% and 20% could promote stand growth well, the growth percentage of volume reached the maximum of 9.5%. The diameter distribution kept an inverse J-shaped nearly, the volume proportion of imperial diameter class was more than that of tending spruce-fir forest, and most occupied 30% to 40% of total volume in the last survey. The ratio of stand conifer to broadleaf volume was almost between 6:4 to 8:2.(3) Through analysis of the relation between stand volume and growth percentage, PAI for all plots, results showed that while the growth percentage of volume was above 6%, PAI was almost larger than 8 m3/hm2. Meanwhile the optimal stand structure had the volume between 100 and 250 m3/hm2, tree number of 700 to 1000 n/hm2, average q value of DBH of 1.2 to 1.5, ratio of stand conifer to broadleaf volume of 6:4 to 8:2. The optimal volume proportion of different diameter classes was:small(8-12 cm):medium(14-24 cm):large(26-36 cm):imperial(> 36 cm)=1:2:3:4. The selective cutting cycle was about between 6 and 10 years.(4) 13 factors of stand growth and structure were integrated into 3 typical variables through principal components analysis, i.e., stand primary feature, stand density and diameter class structure(number of trees and volume), which will provide some references for subsequent stand restoration evaluation after cutting. According to stand condition in this research, the management mode of control method plots should carry on, and best cutting intensity and cycle should be set by stand growth at the time, then take some measures to promote natural generation. The management of tending spruce-fir forest can refer to control method, following low intensity selective cutting with heavy cutting when stands come to mature with the growth percentage of volume lower than 3%, which can maintain high forest site productivity, promote the growth of imperial tree, adjust stand structure gradually and ensure the health and stability of forest ecosystem.