Crown scale and growth space demands of main tree species in urban forest

ObjectiveThe size of canopy directly affected the ecological value of the trees, and exploring the reasonable demand for the growth of the trees was of great significance to the construction and management of urban forests. In this study, the main 10 dominated tree species in the Ring Park around Hefei City, eastern China were taken as research objects.

MethodUsing the sample surveyed method, 57 fixed samples of 6 scenic areas in the park were selected as sampling site. On the basis of investigation of crown width, DBH and tree height, the linear regression method and allometric method were used to construct the optimal regression model of crown width, tree height with DBH. After using the box diagram to check the outliers, the best suitable spatial scale for the tree growth was predicted.

Result(1) There were positive correlations between crown width and DBH, tree height and DBH, but by comparing the results of two models, it could be found that the values of R² of allometric models were higher than the simple regression models, and the value was more than 0.3 except Koelreuteria paniculata and Platycladus orientalis. While the distribution ranges of RMSE of allometric models were generally less than the simple regression, and the values ranged between 0.2-0.3. In addition to Cedrus deodara, the F values of allometric models were higher than that of simple regression. Synthetically, the fitting rate of the allometric model was better than that of the simple regression model. (2) Not all the crown width and tree height of 10 tree species were highly correlated with the height of DBH. The crown width-DBH models of Ginkgo biloba, Ligustrum lucidum and Photinia davidsoniae were fitted well, with 0.793, 0.757 and 0.665 were R² values, respectively. The tree height-DBH models of Ginkgo biloba, Koelreuteria paniculata and Cedrus deodara were fit, and the R² values were 0.772, 0.579 and 0.547. While the correlation between crown width and DBH models of Koelreuteria paniculata and Platycladus orientalis was lower, the R² values were 0.096 and 0.188. The tree height-DBH models of Robinia pseudoacacia, Broussonetia papyrifera and Osmanthus fragrans were poor, and the R² values were 0.065, 0.010 and 0.112. (3) The regression of quantiles was selected to study allometry. The allometric models of 10 species of trees were constructed and the analyses were discussed under the regression of 95 % quantile. Taking the average DBH of 15cm as an example, it was estimated that when the DBH was 15cm, the crown width and tree height of the 10 tree species in the appropriate growth space were estimated.

ConclusionThe estimated values of the optimal model constructed in this paper were significant, which indicated that the crown width and tree height variables had a significant effect on the change of DBH in the Ring Park around Hefei City. The fitting accuracy of crown width-DBH model was slightly higher than that of tree height-DBH model.