366 Jim: Urban Forest Census in Hong Kong Arboriculture & Urban Forestry 2008. 34(6):366–378. Multipurpose Census Methodology to Assess Urban Forest Structure in Hong Kong C.Y. Jim Abstract. Surveys of urban forests in the compact city environment of Hong Kong were initiated in 1985 and regularly updated thereafter. Roadside trees were evaluated first in a tree census and reported in this article followed by urban parks, public housing estates, and special habitats such as old stone walls or special specimens such as heritage trees. The survey method aimed at collecting comprehensive data to echo both tree conditions and tree–environmental interactions. Detailed information was gleaned, with the help of well-trained assistants, on tree sites, tree growing space, tree structure, and tree defects and disorders. A field record form was designed, pilot-tested, and refined to solicit responses to multiple choices or direct measurements to minimize subjectivity and errors in data recording and entry. The study also identified potential planting sites, registering suitability for tree growth, site characteristics, and dimensions. Data fields were designed to be quantitative or convertible to ordinal ranks to facilitate statistical analysis. Locations of trees and planting sites were marked on large-scale maps to permit spatial analysis. Besides statistical analysis, community ecology attributes and custom-designed indices were used to assess urban forest structure. The multipurpose method could be appropriately adjusted for use in other compact city areas. Key Words. Compact city; forest structure; heritage tree; Hong Kong; planting plan; species composition; species diversity; tree census. Tree surveys have been widely used by urban foresters to collect objective and quantitative data on trees and their growth envi- ronment (Johannsen 1975; Weinstein 1983). Understanding the resource base provides the initial step to improve and rationalize urban forest management and raise the cost–benefit efficiency of tree programs (Tate 1985). The data could facilitate in-depth research into the tree–habitat relationship and evaluate the ben- efits and functions of urban greening. Whereas researchers are satisfied with a representative sample, many municipal authori- ties would adopt the inventory or census approach to study every tree within their jurisdiction. The use of computer technology to store and analyze data was reported initially by McPherson et al. (1985) and Warrick and Williams (1993). Subsequently, developments in information technology triggered the application of the geographic informa- tion system (GIS) spatial analysis tools (Dwyer and Miller 1999; Pauleit and Duhme 2000). Street and park tree inventory has been conducted in different cities, exemplified by Chacalo et al. (1994) in Mexico City, Poracsky and Scott (1999) in Portland, Cheng et al. (2000) in Tokyo, Banks and Brack (2003) in Can- berra, and Frank et al. (2006) in Greater Melbourne. Good- quality tree information gleaned from tree surveys is a key in- gredient of sustainable urban forestry (Dwyer et al. 2003). The urban forest in Hong Kong has been studied since the early 1980s. It began with roadside trees. The tree survey meth- odology was applied to trees planted or growing spontaneously in special ecologic habitats. They include trees of heritage value (Jim 1994a, 2004a, 2005), old stone retaining walls (Jim 1998a), urban parks (Jim 2000), new towns, institutional grounds, rec- reational beaches, and indoor shopping malls. Detailed data on approximately 40,000 urban trees have thus far been collected and used for research and management. A study on 40,000 trees in approximately 100 public housing estates is due for comple- tion in mid-2008. The arboricultural and urban forestry research ©2008 International Society of Arboriculture experience gained in Hong Kong has been applied to other Chi- nese cities, including Guangzhou, Nanjing (Jim and Liu 2001; Jim and Chen 2003), Shenzhen, and Taipei (Jim and Chen 2008). The intensive urban tree studies in Hong Kong have yielded valuable data and insights into the conditions and constraints for tree growth in one of the most compact cities in the world. The findings contribute to the understanding of arboriculture and urban forestry in tropical cities. They have been used by tree managers and informed official policies on tree planting, protec- tion, and management. This article has chosen the broad-based generic studies of roadside trees, complemented where appro- priate by studies in other habitats, to illustrate the comprehensive assessment of urban forests in Hong Kong. It evaluates the ob- jectives, scope, principles, methods, approaches of urban for- estry research, and applications in Hong Kong. Besides biomass structure and species composition, the study explored the inter- play between trees and the tight urban fabric and the potential to improve the quantity and quality of urban trees. The specific research objectives are: 1) to survey existing street trees; 2) to search for potential street-tree planting sites; 3) to interpret the results and offer recommendations; and 4) to design a master planting and management plan. The survey covered all the public roads in the study area. Because the sampling intensity was 100%, the study denoted a tree census. STUDY AREA AND METHODS Where and When Was the Assessment Performed? The study was initiated in 1985 as a preliminary investigation (Jim 1986), in 1994 as a comprehensive tree census (Jim 1994b), and repeated in 2004 as a detailed study of a sample. In the intervening time, surveys were conducted on new roads and
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