376 ft]; large, 10 to 15 m [33 to 49.5 ft]; medium, 5 to 10 m [16.5 to 33 ft]; small, less than 5 m [16.5 ft]) and crown spread of the exceptionally large and large trees (less than 15 m [49.5 ft] and greater than 15 m [49.5 ft] crown diameter) were used to match sites with species. Additional botanical attributes were assessed such as growth form, attractive flowers, native versus exotic origin, and hardiness. The tree survey data confirm the conservative species selec- tion in both government and private projects with overreliance on popular species (Table 3) and implications on disease resis- tance and landscape quality (Raupp et al. 2006). The species homogenization phenomenon (Attorre et al. 2000) has spread from old to new neighborhoods. The species frequency profile could pinpoint the candidates to be weaned, including some excessively planted palms. The strong preference for exotics and the lack of species with attractive blooms could be consciously rectified. The tendency to plant trees with small final dimensions in large planting sites would need some attention. The obstacles to the wider use of natives such as the lack of supply by the landscape trade, inadequate practical experience on their suit- ability for urban use, and meager scientific information could be overcome by relevant policies and actions. An official species palette and guideline on species selection and matching with site conditions could be established by a coalition of landscape pro- fessionals and researchers. The existing species composition and choice highlights the supply-led situation by local tree nurseries, which could gradu- ally be adapted to a demand-led scenario. The seed collection and propagation techniques of local nurseries could be upgraded by training and demonstration schemes to meet the changing demands (Sæbø et al. 2005). Uncommon, rare natives with good performance as registered by the tree survey could be targeted for suitability testing. The choice of species in future planting programs could aim at adjusting the present imbalance in species composition and to enhance urban floristic biodiversity (San- tamour 1990; Frank et al. 2006), which could bring collateral benefits to urban wildlife. Native species with the potential to supply suitable shelter and forage to indigenous wildlife could be targeted. In view of the frequent typhoon attack, the empiric tree performance data could recognize species that are tolerant or susceptible to wind damage. Overall, the results hint that future species choice could extend from aesthetic to ecologic and social considerations (Banks and Brack 2003). The results also yield information on the type and magnitude of construction damages on trees and provide hints to minimize such impacts (Ames and Dewald 2003; Jim 2003). The old trees that grow spontaneously on old stone walls, a unique urban ecologic feature of the city, deserve special conservation efforts (Jim 1998a). The results identify some old or haphazard trees that are approaching their useful and safe lifespan, that demand a well-planned removal and replacement program. The findings on the cracked and raised pavement of sidewalks pinpoint the species with vigorous roots that could be avoided in confined paved areas. A 5-year planting plan was designed to cover the ten urban districts (Table 7). The total number of plantable trees was di- vided into five approximately equal portions to be spread over 5 years. Rather than following strictly objective criteria in using the potential sites, some general principles were adopted in as- signing priority in the planting program. Sites situated in neigh- borhoods with little or no existing trees, and sites that were more ©2008 International Society of Arboriculture Jim: Urban Forest Census in Hong Kong readily available, were targeted first. In addition, localities with high development density and poor environmental condition, that could benefit more from early introduction of greenery, were tackled as soon as possible. The plan should not be regarded as rigid and definitive. Instead, it could be appropriately modified to match the changing opportunities and constraints encountered in the course of implementation. CONCLUSIONS The methods developed for the detailed field evaluation of road- side trees provided useful data to study the intimate relationship between tree growth and the tight urban fabric in a dense city environment. The unique features of the field technique are the microscale assessment and measurement of the planting site and tree dimensions to highlight the intense conflicts between trees and urban structures. The inclusion of a survey of potential plant- ing sites expanded the study. The proposed framework for the systematic identification, characterization, and use of potential planting sites in crowded streetside environs could be applied to other cities. Interpretation of the results permitted understanding of the arboricultural problems that commonly beset roadside trees in a cramped and stressful habitat and offered hints to design planting site, select species, and adjust tree planting and maintenance practices to enhance growth. The experience could be shared with Asian, African, and South American cities, which are commonly densely packed, and with the core commercial heart of Western cities, which have a similar tight town plan and tree growth confinements. Acknowledgments. The grant supports kindly furnished by the munici- pal council and the Seed Funding for Basic Research scheme of the University of Hong Kong are gratefully acknowledged. I also thank the field assistance provided by student helpers of the University of Hong Kong. LITERATURE CITED Alvarez, I.A., G. Del Nero Velasco, H.S. Barbin, A.M.L.P. Lima, and H.T.Z. do Couto. 2005. Comparison of two sampling methods for estimating urban tree density. Journal of Arboriculture 31:209–214. American Forests. 2004. CITYgreen for ArcGIS: Calculating the Value of Nature. American Forests, Washington, DC. 93 pp. Ames, B., and S. Dewald. 2003. Working proactively with developers to preserve urban trees. Cities (London, England) 20:95–100. Attorre, F., M. Bruno, F. Francesconi, R. Valenti, and F. Bruno. 2000. Landscape changes of Rome through tree-lined roads. Landscape and Urban Planning 49:115–128. Banks, J.C.G., and C.L. Brack. 2003. Canberra’s urban forest: Evolution and planning for future landscapes. Urban Forestry and Urban Green- ing 1:151–160. Bradshaw, A.D., B. Hunt, and T. Walmsley. 1995. Trees in the Urban Landscape: Principles and Practice.E&FN Spon, London, UK. 272 pp. Bühler, O., P. Kristoffersen, and S.U. Larsen. 2007. Growth of street trees in Copenhagen with emphasis on the effect of different estab- lishment concepts. Arboriculture and Urban Forestry 33:330–337. Chacalo, A., A. Aldama, and J. Grabinsky. 1994. Street tree inventory in Mexico City. Journal of Arboriculture 20:222–226. Cheng, S., J.R. McBride, and K. Fukunari. 2000. The urban forest of Tokyo. Arboricultural Journal 23:379–392. D’Amato, N.E., T.D. Sydnor, and D.K. Struve. 2002. Urban foresters identify Ohio’s tree needs. Journal of Arboriculture 28:291–301. Dwyer, J.F., D.J. Nowak, and M.H. Noble. 2003. Sustaining urban for- est. Journal of Arboriculture 29:49–55.
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