Effect of habitat traits on tree structure and growth in private gardens

Abstract

Urban domestic gardens (UDG) provide an interesting landscape ecology theme with conservation and biodiversity applications. Effects of habitat traits on tree species composition, spatial distribution and growth performance were studied in private UDG in Hong Kong. Five groups of tree-habitat variables were assessed: species-count per garden, tree-count per garden, lot-frontage width, garden depth, and tree-position in garden. Tree structural damage and growth condition were evaluated by visual tree-assessment techniques. The results recorded 1501 trees representing 72 species distributed in 261 gardens, with heavy bias towards exotic species (81.9 %) and exotic trees (91.1 %). The top-five species contributed 45 % of relative abundance, with higher spatial-occurrence and aggregation indices. Cluster analysis classified habitats into three groups based on species similarity. Correspondence analysis (CA) identified three distinct habitats types: good (cluster A), moderate (cluster B), poor (cluster C). Species distribution in CA ordination space was demarcated by structural damage and overall health condition. Nine species fell under the moderate–severe structural damage group, with four in cluster C and another four in clusters A and B. Some 41 species had poor and very poor overall condition, with seven species in cluster A and 14 in cluster C. Species groups were evaluated to inform a species selection strategy. Species adoption by homeowners is molded by habitat traits and joint operation of collective–extrinsic and individualistic–intrinsic influences which have prevented arboreal homogenization and generated spatial differentiation. Measures should address the serious biodiversity gap induced by landscape fashion, nursery-industry supply, and inappropriate species choice.