Effects Of Spatial Structure On Growth Of Poplar-birch Secondary Forest In Taoshan Forest Farm

The secondary poplar-birch forest is a kind of forest communities, which is widelydistributed in area of north and northeast China, and mostly formed in the interference andsabotage such as deforestation, grazing and natural disasters. Secondary poplar-birch foresthas wide distribution and important ecological location, which is the typical forest inTaoshan forest farm, undertaking mission-preventing sand source and guaranteeing thewater source for Beijing and Tianjin area. Extensive-management and unreasonableforest structure of secondary poplar-birch forest caused some serious promlem, such aspoor growth condition, low ecological function, simple biodiversity, serious plant diseases,insect pests and so on, so the sustainable management of the secondary poplar-birch foresthad became an imminent problem.This paper takes the secondary poplar-birch forest in Taoshan forest farm as theresearch object, mainly analysed non-spatial and spatial structure of the secondarypoplar-birch forest by diameter number distribution, weibull distribution function, andangle scale, neighborhood comparison, mixed degree spatial structure parameter. Based onforest spatial structure, we researched the relationship between spatial structure parametersand stand volume, spatial unit volume, diameter growth in different levels, for the sake ofraising economic benefit and operation of secondary poplar-birch forest in Taoshan forestfarm.The tree species of secondary poplar-birch forest in Taoshan forest farm vary fromforest to forest, and part of the stands have attained to the standard of pure forest, somanagement measures should be taken to adjust forest tree species composition. The curveof stand DBH is unimodal, its numerical distribution ranges from6to38cm, and accordwith the weibull distribution model. The type of tree height distribution was similar tounimodal, and the most part of tree height focus on10to12m.The largest proportion about angle scale of the secondary poplar-birch forest is0.5,secondly are0.25and0.75, almost no the proportion of0and1. Random or aggregationdistribution is the stand spatial distribution pattern. The average neighborhood comparisonof secondary poplar-birch forest is about0.5, and different neighborhoodcomparison distribution are basically the same. The distribution frequency of the dominant species birch’s neighborhood comparison determine to a large extent the distribution ofstands, different associated species have a great differences on differentiation. Due to theinfluence of small topographic factors, the mixed degree of different secondarypoplar-birch forest are different. In this study, the average mixed degree of sample plots aremanifested as that, the highest is A1, the secondly is A2, A5to A8sample plots are verylow.Stand volume showed a decreasing trend when the average angle scale and mixeddegree of stand increasing. In addition, there is no significant relationship between theneighborhood comparison and stand volume.When the reference tree’s angle scale is0.5, the spatial unit volume that composed ofit and its closed neighboring trees is highest, and the spatial unit volume is the lowest whenthe angle scale is0or1about reference tree. The neighborhood comparison of thereference tree have no obvious relationship with the stand volume that formed by it. Forthe mixed degree, when the reference tree’s mixed degree is lower, the spatial unit volumethat composed of the reference tree and its closed neighboring trees manifested as lowertoo, there is a negative correlation among them. In the forest which mixed degree with alow degree, the descent speed of the spatial unit volume is slower when the reference tree’smixed degree rising.The trees can be divided into2groups according to the growth of differentneighborhood comparison tree. Namely, the one group include the most dominant tree anddominant tree which neighborhood comparison are0and0.25, the another group includethe intermediate tree, bad attitude tree and the most bad attitude tree which neighborhoodcomparison are0.5,0.75and1. There is no significant difference bet-ween within group,but exist significant difference between the two groups. The rea-son for thesignificant difference of growth between groups is the different of thecompetitive pressure and open comparison. In addition, the most competitive time of theforest trees is10~20a, it is the best time to managing the forest stand and adjust reasonabledensity.