ABSTRACT
Understanding the factors that affect tree hazard condition is important to mitigate it. To quantify these factors for Fraxinus americana L., Morus nigra L., and Populus deltoides Marshall trees we have conducted a survey recording their hazard rating according to the TRAQ methodology. The following covariates were registered for each tree: the number of single tree defects in root collar, trunk and scaffold branches, trunk diameter at breast height (DBH), crown class, crown asymmetry, and the size of the tree pit. A multi-category logistic regression model was fitted to the data using the backward step-wise procedure. Among the factors considered, only the species, crown class, number of single defects in root collar and scaffold branches significantly affected the tree hazard condition. P. deltoids trees had higher values of hazard compared to F. Americana and M. nigra trees. Trees with co-dominant crowns presented a higher probability of being classified as medium and high hazardous than trees with suppressed and dominant crowns. Finally, every single defect observed on root collar and scaffold branches increased the probability of a tree being of medium or high hazardous, by about 3.00 and 1.44 times, respectively. Other factors like crown asymmetry, DBH, and the tree pit size did not have a significant effect on the score of tree hazard. Our results demonstrate that the species selection is an important tool to manage urban tree hazard under the study conditions. At the species level, efforts should be directed towards minimizing defects in root collar, trunk and scaffold branches.
Keywords:
Tree defects; Failure potential; TRAQ methodology
