Species diversity and performance assessment of trees in domestic gardens

• We studied species diversity and tree performance in domestic gardens in Hong Kong.
• Tree species composition was dominated by a small number of popular exotic species.
• Tree species distribution was strongly associated with some habitat-tree variables.
• Indicators of poor tree performance correlated with tree position and confinement.
• Findings could enhance contribution of domestic gardens to urban biodiversity.

Domestic gardens, as an important component of urban green infrastructure, could make significant contributions to urban biodiversity. This study evaluated species composition, floristic diversity, amenity-ecological characteristics, habitat condition, and performance of trees in domestic gardens in urban Hong Kong. The 1501 individual trees belonged to 72 species, 61 genera and 36 families, with domination by a small cohort of popular species. Tree composition skewed heavily toward exotic species count (81.9%) and tree count (91.1%). The most prominent amenity-ecological attributes were fast growth and establishment and interesting tree form and foliage, accounting respectively for 38, 32 and 27 species. Nonmetric Multidimensional Scaling (NMDS) indicated strong association between species distribution in domestic gardens and habitat-tree variables, such as tree density, tree aggregation, species aggregation, lots with trees and house lots. Redundancy Analysis (RDA) showed positive correlation (p < 0.05) between tree and species counts and lot frontage and garden depth. Detrended Correspondence Analysis (DCA) identified 16 species with relatively widespread presence in moderate or severe structural damage groups; and 22 species with very poor or poor overall condition. RDA further demonstrated positive correlation (p < 0.05) between structural damage and overall condition, and tree position and confinement type. The contribution of domestic gardens in the urban greening program could be improved with appropriate incentives, and be integrated into a comprehensive landscape plan. The management implications with reference to preservation and enhancement of garden trees could be applied to south China and other cities.