112 urban gardens and country parks (Zhang et al. 2017). As poorer air quality was usually associated with traf- fic, the trees were further divided into “street trees” and “non-street trees.” We also measured the road widths adjacent to the measured trees. Roads with < 5-m width were classified as “narrow”; 5- to 7-m as “medium”; and > 7-m as “wide.” Trees situated on other land uses (such as parks) but adjacent to roads were also identified as “street trees,” but trees in pedestrian-only streets were recognized as “non- street trees.” The non-street trees were classified into “trees in parks,” “trees in built-up area,” and “trees at remote area.” “Urban Park” referred to relatively large public green sites such as Guia Municipal Park, Camões Garden, Lou Lim Ieoc Garden, Garden of Commander Ho Yin, Montanha Russa Park, and S. Francisco Garden. “Built-up area” was occluded in residential lots, building compounds, religious sites, and other areas influenced by development. “Remote area” included more natural environments such as country parks, slopes, or seashores. The tree commu- nity ecology was evaluated by detrended correspon- dence analysis (DCA) in R with the “vegan” package (Oksanen et al. 2017). We analyzed the relationships among tree height, crown area, dbh, leaf area (calculated from the i-Tree Eco model), and tree locations by principal compo- nent analysis (PCA) in R with the “ggfortify” pack- age (Horikoshi and Tang 2016). The heritage trees were grouped into genera due to the limited information of the i-Tree Eco database on south China native species. The grouping also helped to tackle the large proportion of uncommon or rare species (≤ 3 trees per species). The relationships of tree dimensions against ages were analyzed by Pear- son correlation with SPSS Version 22 (IBM Corp.) for the 10 most common genera. We ranked the top 10 genera by their ecosystem- service capacity and analyzed their mean values by a nonparametric independent samples Kruskal-Wallis Test, followed by a series of Mann-Whitney tests to identify the pairs that differed significantly from the others. The ecosystem services were compared between street trees and non-street trees, as well as between native and exotic species by an independent samples t-test. These analyses were performed by SPSS Version 22 (IBM Corp.). The associations of ecosystem services by different tree families were analyzed by principal component analysis (PCA) in ©2020 International Society of Arboriculture Lai et al: Heritage Trees in Macau R with the “ggfortify” package (Horikoshi and Tang 2016). RESULTS AND DISCUSSION Tree Composition This study analyzed 790 heritage trees with age ≥ 100 years in Macau. The trees were composed of 289 street trees (36.6%) and 300 native trees (38.0%) (Table 1). Figure 1 indicates tree distribution patterns by six habitat types. Roads with different widths had a similar tree composition, but the narrow roads had more Ficus spp. Tree composition at roadsides (all three width classes) was similar to “built-up area,” but differed from “remote area” and “urban park.” Small land lots surrounded by roads have been a common development mode since the founding of Macau in the 1550s. Trees along such roadsides and in scattered tree pits or in small green pockets within the governmental, institutional, and private residen- tial areas formed a finely divided and mixed land-use pattern. The confined and stressful habitat conditions in these cloistered sites are similar to the circum- stances at roadsides, which explained the similarity in tree compositions of the two types of sites. Mean- while, the “remote area” of the countryside and low-maintenance slopes or seashore favored species with voluntary-growth capability. Thus, such natural or ruderal habitats were characterized by common native genera of Celtis, Pterospermum, and Syzyg- ium. In contrast, common ornamental and mainly exotic species in genera Albizia, Aleurites, Bombax, Cinnamomum, Delonix, Litsea, Plumeria, and Podo- carpus were found in urban parks. Tree Dimensions and Age Heritage trees denoted the largest urban trees in Macau, with a mean dbh of 78.2 cm and a mean height of 12.4 m. In aggregate, they covered 68,710.4 m2 crown area and provided 354,841.5 m2 of of leaf area. The solitary Macaranga sp. had the largest canopy of the heritage tree species in Macau, with a crown area of 283.5 m2 and a leaf area of 1,247.5 m2 . The domi- nant Ficus spp. covered 39,587 m2 (57.6% of total) and provided 204,744 m2 of crown area of leaf area (57.7% of total)(Table 1). The principal component analysis explored the relationships among tree height, crown area, dbh, leaf area, and age of the 10 most common genera reck- oned by the number of trees per genus (Figure 2).
March 2020
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