| Thinning operations are the main technical means of forest management activities,which play an important role in promoting the growth of retained trees,improving the structure of the forest,increasing the sTability of the forest,and achieving the precise improvement of forest quality.Different forest types and forest stand status will have different responses to different intensity of thinning.The study of radial growth changes after thinning of forests with different structures can provide theoretical support for formulating reasonable forest management plans based on the actual conditions of the forest.This paper takes the natural secondary forest of Pinus Tableulaeformis in the Guandi Mountain forest area as the research object,sets the standard field of thinning test,and conducts re-examination after thinning for 5 years.Through the changes of diameter at breast height and competitive pressure index of single trees at the beginning and end of the period,the radial growth of single trees and single trees are analyzed.Competitive decompression,revealing the influence of competitive decompression caused by thinning on the radial growth of single trees,Establish a single tree growth mixed effect model that includes the plot effect and the dumb variables of the competitive relief intensity.Under the premise of reflecting the thinning effect,improve the accuracy and reliability of the single tree radial growth model.In order to promote the growth of retained wood,formulate quantitative thinning Technical indicators,precise adjustment of forest stand structure,provide basis for achieving precise forest management.The main research conclusions are as follows:(1)Different intensities of thinning for natural secondary forests of Pinus tabulaeformis in the Guandi Mountain forest area can effectively reduce the competitive pressure of reserved trees,leading to the pressure-relieving effect of thinning of single trees in the forest stand,and significantly increasing the radial growth of single trees of reserved trees.(2)The competitive pressure-relieving effect of thinning on the radial growth of single trees is significantly different between the single trees of different diameter classes.The increase in the radial growth of single trees of each diameter class shows that the size of the radial growth of each diameter class is Ⅱ diameter class>Ⅲ diameter class.Grade>Ⅰ diameter grade.The radial growth of Ⅰ-diameter single trees under weak thinning conditions will increase significantly,but further increase the intensity of thinning,the radial growth effect of competitive pressure release is no longer significantly improved;Ⅱ-diameter single trees are weak and Under moderate thinning conditions,the radial growth amount increases significantly with the increase of the competitive pressure release intensity,and further increases the thinning intensity,the radial growth effect of the competitive pressure release does not increase significantly;the third diameter single tree is in weak thinning The amount of radial growth under the conditions of strength increases continuously with the increase of the competitive pressure release strength.The size of the crown significantly improves the radial growth,and the size of the different competitive pressure relief is affected.(3)The influence of competition pressure on the radial growth of individual trees in the natural secondary forest of Pinus tabulaeformis gradually increases with age.However,after the third instar level,the competition in the radial growth of individual trees in each age class has different influences on individual trees.Not big.For different age tree heights,the effect of competition is that the height of single trees below 35 years is significantly affected by competition,and the height of single trees above 35 years is not affected by competition.The Gompertz equation can better fit the height of a single tree,and the model determination coefficient(R2=0.6)(4)For forests that adopt management activities,the establishment of a single-wood radial growth model must consider the effect of thinning pressure relief to improve the adaptability and fitting accuracy of the model.For this reason,this study adds the intensity of competitive pressure relief as a dummy variable.The established exponential model is In(G后)=-1.382+0.6489 log(D)+0.00013D20.00279CI-0.00958N+0.04CCI1+0.104CCI2+0.2048CCI3 the sample plot effect is added as a random effect to the competitive pressure relief intensity parameter,which can significantly improve the accuracy of the model. |
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