Arboriculture & Urban Forestry 48(4): July 2022 were included. Five species were dropped due to insufficient sample size for reliable prediction equa- tion (Keith 2019). To enhance the comprehensive- ness of the results, error terms and confidence intervals of the regression coefficients were reported. Binary logistic regression was administered to pre- dict the presence of protruding parts. The 3 aforemen- tioned scenarios, namely (1) protruding roots, (2) protruding flares, and (3) protruding roots and/or flares, were adopted. DBH, H, and lean angle functioned as dendrometric factors, whereas pavement width, open soil area, setback, and pavement material were classi- fied as habitat factors. Following Hilbert et al. (2020), the unit of measure used for DBH was centimetres, so that odds ratio values could be more easily inter- preted. Model statistics (Χ 2 ), pseudo R2 , and predic- tion accuracy values (Yes% and No%) were presented, followed by the effect of each factor on the odds ratio of the 3 scenarios. General models containing all 1,100 trees as well as species-specific models were presented. Finally, multiple regression was conducted to pre- dict the magnitude of protrusion in the 3 scenarios. The magnitude of protrusion was synonymous to the length of the protruding part under investigation in the respective scenario. Again, the same set of den- drometric and habitat factors served as predictors. The model statistics and regression coefficients of all predictors were reported. Due to the method of mea- surement, longer protruding roots and/or flares led to larger TFD. As a result, TFD was removed from the multiple regression models. The length of protruding roots and flares was a more-direct indicator of poten- tial conflicts between trees and pavement, thus receiv- ing emphasis in the prediction models. Similar to the logistic regression, both general and species-specific models were constructed. RESULTS Overview of Dendrometric Factors Among large-tree species, the species rankings of DBH and TFD showed similarities (Table 1a). Ficus altissima featured the largest mean DBH (0.754 m), significantly exceeding the congeneric F. microcarpa (0.467 m). Similarly, in terms of TFD, 3 species showed a statistically distinct, descending rank: F. altissima (2.504 m) > F. microcarpa (1.797 m) > Del- onix regia (0.956 m). For intermediate species, DBH and TFD showed differences in the ranking with respect to tree species. 221 A clearly delineated group with intermediate TFD values (0.501 to 0.653 m) consisted of species such as Aleurites moluccanus and Bombax ceiba (Table 1a). However, DBH distributions of intermediate species displayed complicated statistical grouping. For exam- ple, A. moluccanus belonged to 3 homogeneous groups. Even more complicated grouping was observed in H (Table 1a). For instance, Casuarina equisetifolia, whose mean H reached 13.45 m, was significantly taller than all other species except F. microcarpa (11.94 m). Meanwhile, the latter was statistically comparable to upright species such as A. moluccanus. Complex dis- tribution patterns also existed in the case of lean angle. Therefore, species-specific patterns in dendro- metric distributions would justify further analyses at species level. Overview of Habitat Factors Casuarina equisetifolia and F. altissima, with respective mean pavement width of 9.168 m and 7.277 m, were planted in significantly wider pavements (Table 1b). Much narrower pavements were observed for the rest of the species with mean width from 3.177 to 5.967 m. Except Lagerstroemia speciosa, all species had notably more samples along brick pavement than concrete pavement. Ficus altissima and F. microcarpa enjoyed signifi- cantly larger open soil area than any non-Ficus spe- cies at 5.859 m2 and 3.042 m2 , respectively (Table 1b). Large-statured but non-Ficus species, such as A. moluccanus, B. ceiba, and D. regia, had intermediate mean open soil area from 1.312 to 1.689 m2 . Lager- stroemia speciosa had the smallest mean open soil area at 0.486 m2 . The widest mean setback, 3.894 m, was found for F. altissima, significantly exceeding that of all other species (Table 1b). Large trees could be planted adja- cent to narrow setback. For example, A. moluccanus had significantly narrower mean setback (0.376 m) than most species. Large and small trees may show statistical homogeneity in mean setback width, such as F. microcarpa (1.487 m) and Xanthostemon chry- santhus (1.353 m). Allometric Model for TFD Prediction For all species, DBH was a significant predictor of TFD in linear regression (Table 2a). The model with the highest R2 value belonged to A. alexandrae (R2 = 0.804), the only monocot in the list, whereas Michelia × alba ©2022 International Society of Arboriculture
July 2022
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