| The stem form of trees is the key factor in the calculation of volume,which is often expressed by form factor,taper,form quotient and so on.The stem form is obviously different due to the internal factors and external conditions of the tree.Taking the single tree of Cunninghamia lanceolata plantation in Hunan as the research object,based on two stem form indicators of form factor and taper,using coefficient of variation method,variance analysis method,Pearson correlation analysis,multiple stepwise regression analysis,mixed effect models and other methods,From the quantitative attributes(form factor)and quality attributes(taper)of C.lanceolata stem form,discuss the stability,difference and significant influencing factors of single tree stem form of C.lanceolata plantation in Hunan,and comprehensively analyze the dynamics of fir stem form under different conditions To establish a comprehensive forecasting model for the single tree stem form indexes of C.lanceolata plantation.The results of the study are as follows:(1)The form factor of single tree in C.lanceolata plantation have different stability in different regions,tree height levels and diameter-classes.The stability of the experimental form factor is generally better than that of the breast-height form factor.However,after comparison of the area,tree height levels and diameter-classes,it is found that in some areas(Changde and Chenzhou),low tree height levels(tree height levels 8-10)and the small diameter-classes(diameter-classes 10-14),the stability of breast-height form factor of single tree of C.lanceolata plantation is better than that of the experimental form factor.However,the experimental form factor has the characteristics that its stability gradually increases with the growth of the trees and is better than the breast-height form factor.(2)There are differences in the mean value of the form factor of single tree in C.lanceolata plantation in different regions,tree height levels and diameter-classes.The average breast-height form factor and average experimental form factor of C.lanceolata in Changde City are the largest(0.5915 and 0.4681,respectively),and the average breast-height form factor and average experimental form factor of C.lanceolata in Xiangxi Prefecture are the smallest(0.4710 and 0.3756,respectively);the overall regional difference is shown by from the east(Hengyang City,Shaoyang City)to the west(Xiangxi Prefecture),from the north(Changde City,Yiyang City)to the south(Yongzhou City,Chenzhou City),the trend gradually decreases.The mean value of breast-height form factor is negatively correlated with tree height and diameter at breast height,that is,the breast-height form factor decreases with the increase of tree height and diameter.The experimental form factor increases first and then decreases with the increase of tree height levels and diameter-classes.(3)The results of Pearson correlation analysis showed that the breast-height form factor and experimental form factor of individual trees in Hunan Clanceolata plantation were significantly positively correlated with slope and stand density(p<0.05),the form factor increases with the increase of slope and forest density;and significantly negatively correlated with altitude and age(p<0.05),the form factor decreases with the increase of altitude and age.Since the change of form factor will be affected by the comprehensive effects of various factors,the main influencing factors are further screened out by using multiple stepwise regression analysis.The results of multiple stepwise regression analysis showed that altitude,slope,stand density,diameter at breast height and tree height are the key indicators that affect the stem form of C.lanceolata.The regression equation of breast-height form factor is:f1.3=0.609-8.382×10-5×HB+0.002×PD+3.334×10-5×N-0.004×H-0.006×D;the experimental form factor regression equation is:f(?)=0.363-5.313×10-5×HB+0.001×PD+3.095×10-5×N+0.009×H+0.004×D.("HB"means altitude;"PD"means slope;"N" means forest density)(4)There are differences in the relative taper variation degree at each position of the C.lanceolata stem.The results of the coefficient of variation method show that the variation coefficient of the taper at different tree heights of the C.lanceolata stem ranges from 0.1015 to 0.3871,and the variation range at different tree heights is:0.2<0.4<0.6<0.8<base.The coefficient of variation of the relative middle part of the stem(relative height 0.2 and relative height 0.4)is small,that is,the difference in taper between C.lanceolata stem is less obvious,while the base and relative position higher(relative height 0.8 and relative height 0.6)The coefficient of variation is larger,that is,the difference in taper between the relative positions of the stem is more obvious.(5)The relative taper of each part of the stem of Hunan C.lanceolata plantation varies with the growth of the C.lanceolata itself:the taper of the middle part(relative high 0.2 and 0.4)of the stem of C.lanceolata has a less obvious difference with the increase of tree height and diameter at breast height,but at the base of the stem and the taper changes at higher places(relative high 0.6 and 0.8)are more significant,The taper at the base gradually decreases,and the taper at the top gradually increases.the increase in tree height and diameter at breast height leads to an increase in the overall taper of the stem.(6)The taper of each part of the stem of Hunan C.lanceolata plantation shows different changes under different site factors and stand factors.With the increase of a certain slope,the taper of the base of the C.lanceolata stem shows an overall upward trend,which means that with the increase of the slope,the diameter of the base of the stem grows larger;the relative taper of the stem is 0.2,0.4,0.6,0.8.With the increase of the grade of slope,the overall trend is decreasing,but the effect is not significant.The average taper of single tree stem of C.lanceolata plantation shows less obvious regularity with the change of slope.Altitude changes have a significant impact on the taper of each part of the stem of the C.lanceolata plantation and the average taper of the stem;the relative taper of the stem base decreases with the increase in altitude,and the relative taper of the other stem will increase with the increase in altitude.The increase in altitude increases;therefore,the increase in altitude leads to an increase in the overall taper of the individual tree stem of the C.lanceolata plantation,and the quality of the stems is poor.Stand density has a particularly significant effect on the taper of each part of the stem of C.lanceolata.With the increase of the density grade,the average taper of each relative height of the stem will decrease.The overall average taper of the stem in high-density forest stands is small,and that of low-density forest The overall average taper of the stem within the branches is large;high-density forest stands can not only increase the number of C.lanceolata stem,but also improve the quality of C.lanceolata stem.Using the mixed effects model,the altitude,slope and stand density are added to the taper equation in the form of random effects,and the influence of each factor on the taper equation is analyzed.The results show that Altitude,slope and forest density all have an impact on the taper equation,so it is necessary to consider its influence factors in the construction of the taper equation describing the stem form.Among them,the taper equation with density effect has the best fitting accuracy,indicating that the density factor has the most obvious influence on the taper equation of C.lanceolata. |
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