Research On The Stand Structure Characteristics Of Two Typical Natural Secondary Forests In Great Xing'an Mountains

Whether a forest can perform its function depends on the merits of its structure,especially the spatial structure of the stand.It has irreplaceable value for the sustainable management of the forest.In this paper,the natural secondary forest the Great Xing'an Mountains was selected as the study site.The diameter distribution of the forest stands was studied with five probability distribution models.The spatial structure index(Preference value PV,optimization objective function FSI and comprehensive distance evaluation CDEV)were used to analyze its spatial structure,and aim to find out the natural secondary forest stand structure characteristics in the Great Xing'an Mountains that provide a theoretical basis for forest structured management in the area.In addition,16 plots were divided into two types of forests that the differences in the structural characteristics of the two forest types(natural secondary larch forest and natural secondary mixed forest)and their tree species were compared using a multi-variate distribution method.The microenvironment characteristics of the forests based on the four spatial structure parameters were also analyzed that provided a more concise approach to determining feller lumber.(1)The tree species composition and diameter structure of the stand indicate that the tree structure of this stand is relatively single,mainly including larch,Mongolian oak,white birch,black birch,and poplar.The DBH of this forest stand generally shows an asymmetrical mountain-like distribution with high in the middle and low on both sides.The characteristics of the DBH distribution show that the lognormal distribution and the gamma distribution have a good effect,which basically accords with the development law of natural forests.It can be used to describe and predict the development of different stand diameters.(2)The spatial structure characteristics of different stands indicate that more than 1/3 of the plots are randomly distributed,and each standard plot which randomly distributed the proportion of tree quantity is the highest.The proportion of random distribution of each tree species is above 50%.The overall forest is on a state of the doctrine of the mean,and the DBH size differentiation of the trees in their respective structural units is more balanced,and the differences in DBH dominance of different tree species are more obvious.There is a huge relationship between the mingling degree and the composition of tree species,but it is not the only influencing factor.Relatively few tree species have a high degree of spatial isolation,such as poplar and birch,which are abundant and well mixed.The forest canopy is relatively dense,and the frequency of the proportion of each tree species from very dense grade(C=1.00)to very sparse grade(C=0.00)decreases in order.Very dense people can be classified into the selective logging range.(3)Based on the comprehensive evaluation of the spatial structure indexes,it was found that the correlation between the average value of the four structural parameters of the trees and the FSI index was tested,and only the average mixing degree value had a significant correlation with the FSI value.Based on this,the importance ranking of each parameter was determined.CDEV's evaluation of the spatial structure showed that the Mongolian oak-black birch mixed forest(with a stand density of 1400 plants per hectare)had the best spatial structure and could provide a reference for structural adjustment;the larch secondary forest(with a stand density of 1656 plants per hectare)had the worst spatial structure.Overall,the spatial structure of the Larix olgensis secondary forest is at a medium level and its spatial heterogeneity is low.The forest is still in an ecological restoration state.(4)The N-variate distribution of the spatial structure parameters of the two forest types indicates that the combination of the structures in the two forest types(C=0.50,W=0.50,M=1.00,and U=0.00)will become the optimal 4 adjacent stand structure unit.Similarly,extremely inferior trees which are in a Clumped distribution with the 4 same species of trees around their and extremely dense canopies will be the first choice for logging.And trees with two no-better structure will become the second choice for logging.Then,there are three parameters of the structure are no-better will become the third choice for logging,and so on.