Arboriculture & Urban Forestry 34(6): November 2008 existing roads with newly planted trees or notable tree replace- ments. The study area covered the built-up parts of the core around Victoria Harbor. It included ten urban districts with 124 km2 (49.6 mi2) containing 3.28 million people in 0.94 million households. The exceptionally high development density in the compact city reaches an average of 26,452 persons/km2, and peak spots exceed 100,000 persons/km2. The city was founded in 1841, but most parts have been redeveloped to a high intensity, especially in the last four decades. The developed areas have high coverage by buildings and roads with little spaces for greening. Built-up areas are often completely sealed by concrete, asphalt, or buildings and most roadsides have no planting strips or tree pits. Many development sites have 100% site coverage with no room left for intralot trees. Urban renewal tended to increase the site coverage and building density and eliminate existing trees and plantable spaces. Con- tinual infilling of low-density sites often obliterated on-site trees. Pavements are narrow and heavily used with little chance for tree planting. Frequent road excavations and trenching regularly in- jure tree roots. The survey focused on roadside trees, which are the most cramped and stressful tree sites. What Data Were Collected? The study collected two sets of data. The first covered existing roadside trees with the help of a field record form (Table 1). It was pilot-tested and refined before actual data collection. It gath- ered detailed data on the roadside microhabitat, including gen- eral site conditions and specific tree growth space characteriza- tion. It then measured tree structural attributes followed by sys- tematic assessment of critical morphologic symptoms of growth problems. It was necessary to define the scope of the study to focus on the target trees. Roadside trees included those found in the fol- lowing habitats: 1) pavement; 2) planting spaces in the form of tree lawn, tree strip, or raised planting bed that are situated between the curb and the property line; 3) incidental plots of public land that are physically contiguous to the pavement and construed as part and parcel of a street; 4) central divider or road–median positions; 5) traffic islands and roundabouts sur- rounded by carriageways but not designed as gardens or other formal amenity open spaces; 6) spaces below flyovers or foot bridges; and 7) planters, both fixed and movable types, placed on the previously mentioned habitats. Trees in the following types of habitats were excluded from the survey: 1) slopes adjacent to roads; 2) along nonbuilt-up stretches of roads; 3) roads with restricted access to the general public; and 4) trees lying within building land lots. The second part of the study searched for potential tree plant- ing sites at roadsides based on a separate record form (Table 2). The same inclusions and exclusions listed previously were adopted. As a result of the tight roadside spaces, the three- dimensional volume and shape of the potential planting site were emphasized. Each potential planting site was assessed according to building setback, land use, and adjacent surface type (sealed by concrete, porous pavers, or open soil). The dimensions of the plantable corridor were measured, including ground width, building awning width, awning height, site length, number of traffic lanes, and presence of adjacent car parking space (Figure 1). The boundaries of all potential planting sites were drawn on large-scale (1:1,000) maps. The findings were used to design a 5-year planting plan. 367 How Were the Data Collected? The tree survey was preceded by a reconnaissance of roadside trees in different kinds of sites in the study area to learn about tree growth, environmental impacts, and tree responses. The rather common physical and physiological constraints to tree growth were emphasized. Knowledge about the acute limitations at roadsides helped to design the field record form (Table 1). University students in geography or ecology with field work experience were trained as research assistants. Each team with two members was assigned a work area. The study was labor- intensive and time-consuming, demanding many hours of field assessments. It was important to minimize subjectivity and to calibrate judgment, especially regarding tree defects and disorders. Training began as induction lectures to expound basic con- cepts in arboriculture, urban forestry, and site and tree charac- teristics. The lectures were abundantly illustrated with color slides of local roadside trees. Visual images were far more ef- fective in conveying information and leaving recallable imprints. Essential visual guides to common arboricultural problems (e.g., Matheny and Clark 1994; Lonsdale 2000) and key reference books (e.g., Grey and Deneke 1986; Shigo 1991; Bradshaw et al. 1995; Miller 1996; Watson and Himelick 1997; Harris et al. 2004) were available to the assistants. After acquiring the basic knowledge, the assistants were shown slides of tree–environment and tree defects–disorders sce- narios listed in the record form and practice assessment in the classroom. Relevant concepts were explained to ascertain that data would be collected with good understanding of the under- lying rationales. The helpers also learned the capabilities and limitations of the field observation and measurement methods. It was important to ensure that data collection would be a well- considered and fully understood exercise rather than a mechani- cal and prosaic routine. As an essential part of the interactive and collective learning process, they were encouraged to raise que- ries, discuss, and jointly fill in the record forms. A problem- oriented approach was adopted to learn by questions and answers and through active discussions, participation, engagement, and interactions. The coherent group of 12 students facilitated inten- sive coaching and direct person-to-person communication. On satisfactory completion of classroom training, the assis- tants were taken to different sites to rehearse real-world studies. Their field assessment skills were further honed by hands-on training. Most importantly, misconceptions could be promptly explained, rectified, or dispelled. The critical concern of stan- dardization was gradually inculcated. Thereafter, they proceeded to collect live data. Initially, the author took turns accompanying different groups in the field to observe their work and provide comments and advice. They also recorded queries encountered in the survey and discussed these with the author on a regular basis. All initial data were checked for accuracy and consistence. Gradually the need for monitoring was reduced as they gained experience and confidence. As a result of the diverse roadside tree flora in the tropical city, species identification presented challenges. Students learn to recognize common species in an urban park. Each group was equipped with reference books with tree photographs, botanical descriptions, and a dichotomous identification key (Thrower 1988; Jim 1990). Botanical references of the nearby cities of Guangzhou (Hou 1956; South China Botanical Institute 1987, 1991, 1995, 2000, 2003, 2005, 2006) and Taiwan (Lin 1960), ©2008 International Society of Arboriculture
November 2008
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