| After many year's over-logging in timber forests of Greater Higgnan Montains,the forest structures were becoming imbalance and the stability was decreased.For better structure recovery and growth,the experiments were conducted with various thinning intensities in the study area to investigate the optimal thinning intensity,further to improve the ecology environment of the timber forests and optimize the management results.In the study,20 timber forest plots were selected numbered with 1 to 20 in Daxinganling mountains.The plots were reformed in accordance with the different thinning intensities,and the effects of thinning were investigated on the forest soil and forest growth in the plots.(1)The soil of 20 plots was classifed by using the fuzzy clustering analysis method,and consequetnly the F-statistic was employed to determine the optimal threshold value of ?.Accordingly,the soil of all plots was divided into 3 categories as following described:for the group one,the organic matter and the total N were lower,and the soil physical properties was poorer;for the group two,the total phosphorus and total potassium content were lower,and the soil physical properties was better;for the group three,the available phosphorus and available potassium content were lower.(2)The gray correlation method was used to analyze the soil fertility comprehensively in the timber forest plots relating to the various thinning.The correlation was ranked as plot 4(0.775)>plot 18(0.761)>plot 5(0.699)>plot 11(0.657)>plot 3(0.609)>plot 6(0.592)>plot 17(0.542)>1 plot(0.537).The results showed that,the general soil fertility evaluation increased firstly and then decreased with the thinning intensity increasing.(3)The thinning intensities had obvious influences on the spring soil respiration,although the effect was in weak fluctuations.The overall trend of influences was that,when the thinning intensity was lower,the soil respiration was increased with increasing thinning intensities;when the thinning intensity was higher,the soil respiration was decreased with increasing thinning intensities.The reasons for those results were listed as followed:the micro climate in the plot was changed greatly due to the high thinning intensity,and at the same time,the soil was compacted and not conducive to the soil respiration because of the thining activitis with the frequent walking of people and livestock.(4)There are different effects with various thinning intensities on the growth of Larch Plantation in Greater Khingan Range area.The thinning intensity had no significant effects on the height growth of Larch.However,with the increase of the thinning intensity,the diameter growth of larch forests and the individual volume increased,sepecially with the thinning intensity was between 20.86%to 40.1%,the forest volume increased obviously.With no vaiables added,the tree high prediction accuracy was improved by using the vaious tree height prediction models relating to the various thinning intensities,and the models were more simple and more practical.(5)The Larix gmelinii timber forest growth effects was comprehensively evaluated by the principal component analysis with 34 indicators such as species diversity,stand spatial structure,canopy structure,photosynthesis,seedling growth status in the plots with different thinning intensities in the study.The results showed that,the comprehensive evaluation of growth effects was ranked as plot 5(20.86%)>plot 7(12.52%)>plot 18(27.86%)>plot 4(40.01%)>plot 14(59.92%)>plot 3(6.23%)>plot 1(0.00%)>plot 2(34.38%)>plot 15(50.61)>plot 17(67.25%).Especially,the forest growth effects was best with the thinning intensity of 20.85%.Through analyzing the growth effects,the unreasonable factors in the structure characteristics were found during the forest thinning management,and this finding could provide the basis to optimize the management process.Forthmore,the evaluation results is able to provide the evidences and guidances for the Larix gmelinii timber forest management in the Greater Higgnan Mountains. |
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