Effect Of Thinning Intensity On The Structure Of Young Birch Forests

Forest harvesting is one of the main anthropogenic disturbance activities on terrestrialecosystem, and is a main approach of forest management. It has great influence on forestecosystem inevitably. Moderate, regular and measures adjust to local conditions will brightgreat benefits to forest succession and natural regeneration, and are conducive tomaintaining health and stability of forest ecosystem. On the contrary, extensive forestharvesting will result in ecosystem degradation, water and soil loss, low productivity, andserious environmental problems. Therefore, reasonable cutting intensities are veryimportant for creating reasonable stand structure and forming stable ecosystem.This paper takes young Betula platyphylla forest as the research object. Using thediameter number distribution, Weibull distribution function, differences in the diameterstructure among Betula platyphylla forests after different cutting intensities was analyzed.The tree height and stand volume among forests after different cutting intensities werecompared using the method of chi-square test. We also compared the competition betweenplots with competitive indices. By using spatial structure parameter such as mixed degreeand uniform angle index, we analyzed tree species segregation degree and horizontaldistribution characteristics among young Betula platyphylla forests after different cuttingintensities. This study can provide theoretical foundation and technical support formanagement of young Betula platyphylla forests in this area. The main results of the studyare as follows:(1) It is very necessary to conduct definite intensity cutting for young Betulaplatyphylla forest, for forest without cutting, number of major diameter trees decreasesgradually along with age increases, that goes against cultivating of major diameter trees.When cutting intensities are36%and46%,diameter class distribution of tree number isquite reasonable, and imitative effect of Weibull distribution is the best.(2) Reasonable cutting intensities have significant function on growth of forest stand.Moderate cutting can create favourable growing space for forest trees, it has auxo-actionno matter for diameter growth or height growth. Of the four cutting intensities, forest standafter cutting intensity of20%grow slowest, along with increase of cutting intensities,number of forest stand trees decreases and release greater growing space. Throughcontrastive analysis of height of trees, volume growth rate, annual mean increment, change of total increment, we know that cutting intensity of46%is relatively reasonable, and it isbeneficial to growth of current young Betula platyphylla forest(3) Different cutting intensities have great influence on trees competition, we usecompetition indexes to reflect race condition of forest stands after the4cutting intensities,analysis obtained: competition indexes of forest stands after cutting intensities of36%and46%are moderate and in favour of healthy growth of trees. While there are exaggerategaps in forest stand after cutting intensity of55%,that is a waste of space and will reduceholistic stand volume.(4) Through analysis of forest mixed degree after cutting intensities of20%,36%,46%and55%, we can get the following conclusion: forest mixed degree becomes bigger andbigger along with increase of cutting intensities, but mixed degree begin recede whencutting intensities have reached a certain extent, the difference of mixed degree betweenforest stand after cutting intensity of20%and forest stand without cutting is not big, itmeans space will be small when cutting intensity is lesser, tree regeneration is poor, mixeddegree is relatively lower, while mixed degree is relatively lower when cutting intensity is55%, it means exaggerate cutting intensity may cut other tree species besides Betulaplatyphylla, and makes tree species simplex, mixed degree is lower. But mixed degree offorest stand after cutting intensities of36%and46%is bigger, it means cutting intensitiesof36%and46%are beneficial to regeneration of tree species.(5) We can describe spatial structure of forest stand with uniform angle indexparameter, through contrastive analysis of spatial structure of each sample plot, we knowthat logging operation cannot cause more influence on distribution patterns of forest stand,there is no big change of uniform angle index between forest stands, and each sample plotbelongs to aggregated distribution.