Study On Single Tree Crown Structure Of Larix Principis Rupprechtii Natural Forest

Crown is the main place for photosynthesis of trees,It’s size and growth status can better comprehensively reflect the growth vitality of trees,have an important impact on productivity and ecological benefits,and are closely related to stand density.Taking the natural forest of Larix principis rupprechtii in Guandi mountain and Wutai Mountain the research object,this paper selects 51 standard plots with plant number density in density group Ⅰ(1-500 plants·hm-2),density group Ⅱ(500-1000 plants·hm-2),density group Ⅲ(1000-1500 plants·hm-2),density group Ⅳ(1500-2000 plants·hm-2),density group Ⅴ(2000-2500 plants·hm-2)and density group Ⅵ(2500-3000 plants·hm-2).On a single tree scale,Single factor analysis of variance was used to explore the differences of crown structure among different stand density groups,such as crown width,crown length,crown-fullness ratio,crown length rate,crown surface area,crown volume,crown production efficiency,crown extension and crown projection ratio;Pearson simple correlation analysis was used to explore the effects of DBH,H,HCB,CL,MDD,MH and DH on the crown structure.The main results and conclusions are as follows:(1)The results of difference analysis showed that:the absolute indexes such as average,crown width,and crown length showed that density group Ⅰ>density groupⅡ>density group Ⅲ>density group Ⅳ>density group Ⅴ>density group Ⅵ.there were significant differences among different density groups(P<0.05),and the two showed a trend of gradually decreasing with the increase of stand density;The composite indexes such as crown length rate,crown surface area and crown volume also showed that density group Ⅰ>density group Ⅱ>density group Ⅲ>density group Ⅳ>density group Ⅴ>density group Ⅵ.there were significant differences among different density groups(P<0.05),and the overall trend decreased gradually with the increase of stand density;However,the crown structure such as crown perfection,crown extension and crown projection ratio had no obvious distribution trend with the increase of density group;There was no significant difference in crown productivity among the density groups(P>0.05).(2)Pearson correlation analysis showed that:the competitive factors such as plant number density,plot square average diameter(MDD),plot arithmetic average tree height(MH)and plot dominant tree average height(DH)mainly had a significant impact on crown width,crown length,crown surface area and crown volume,and the medium density;had the greatest impact;There was a significant negative correlation between density and average crown width,crown length,crown length rate,crown surface area and crown volume(P<0.001),The correlation and order were as follows:crown surface area=crown volume(-0.42)>crown length(-0.37)=average crown width(-0.37)>crown length rate(-0.18);Density was positively correlated with crown projection ratio and crown completeness(P<0.01),and the correlation between density and density was 0.08;There was no significant correlation between density and crown productivity and crown extension(P>0.05).(3)Among the crown structure indexes,the two composite indexes of crown surface area and crown volume have the greatest response to the change of stand density,followed by crown length and average crown width,and the crown length ratio has the smallest response to the change of stand density,which is the same as the previous research results.Although the crown extension increased with the increase of density,the correlation analysis showed that there was no significant correlation between crown extension and density.Crown width,crown length,crown length ratio,crown productivity,crown-fullness ratio,crown extension and crown projection ratio are the factors that have a significant impact on crown surface area and crown volume.Among them,crown width and crown length are the most important factors,which have a very significant correlation with crown surface area and crown volume(P<0.001).