Effects of diameter at breast height on crown characteristics of Chinese Fir under different canopy density conditions

Abstract

Crown size is an important tree variable included in growth and yield models, which are commonly used as decision鄄support tools in forest management. Crown size is usually described as tree crown width or live crown ratio. Tree crown width and live crown ratio have been found to be a useful measure for tree vigor, and allow one to predict tree growth, mortality and aboveground biomass. In this study, using 103 plots of Cunninghamia lanceolata stand in Huangfengqiao forest farm in Hunan Province as an example, each plot was divided into five classes by stand canopy density (CD) following the rules of CD 逸 0. 8 (Type 1) , 0. 7 臆 CD <0. 8 (Type 2) , 0. 6 臆 CD <0. 7(Type 3) , 0. 5 臆 CD <0. 6 (Type 4) , and CD <0. 5 (Type 5). We analyzed the distribution structure of tree crown width and live crown ratio of each tree for each type, and also analyzed the relationships of tree crown width and diameter at breast height (DBH) , live crown ratio and DBH, respectively. In addition, nonlinear mixed effects models approach was used to describe the random effects of canopy density on tree crown width and live crown ratio. The commonly used logistic model with predictors of DBH and mean diameter at breast height in larger trees (MDL) was selected as a based model to construct mixed effects crown width and live crown ratio models. The prediction accuracy of the developed nonlinear mixed effects crown width and live crown