370 The capacity of each potential planting site to hold trees was evaluated. The data on land use, general environmental quality, three-dimensional site geometry, and existing species frequen- cies were used to develop an elaborate site-by-site matching exercise to find the optimal species. The sites were divided into five lots for implementation over a 5-year period. Neighbor- hoods at present with fewer trees were given priority. A planting material demand profile was developed for advanced ordering to trigger their timely production in nurseries. A key purpose of giving advanced notification to the landscape industry was to facilitate a transformation from the deeply ingrained supply-led to a demand-led situation. Why Were Data on Individual Trees Collected? A comprehensive range of qualitative and quantitative informa- tion was collected (Tables 1 and 2). As far as practicable, mul- tiple-choice answers were given on the record form to minimize subjectivity, ensure consistency, and facilitate data entry. Non- multiple-choice answers were confined to unambiguous attrib- utes such as street name, species names, tree number, distance and angle measurements, or simple counting. The following types of data were solicited for each target tree (Table 1): (1) Basic information: Research assistant group identification number, Field survey date, Map reference, Street name, Tree serial number, Species name in Latin binomial, and Abbreviated species code; (2) Site characteristics: Building setback, recording whether adjacent building was set back from the property boundary to permit tree crown expansion, Land use, choosing one of the ten choices based on offi- cial classification, and Adjacent surface, evaluating access of the soil around the tree to moisture, aeration, and fertilization, including the undesirable sealed surface (concrete, cement, or asphalt), less restrictive pervious pavers, and open soil; (3) Growing space: Roadside location, recording whether the tree was situated within the confines of the pavement, carriageway, property front, road median, street center, terrace or a cul-de-sac, traffic island, incident roadside plot, or other location, Growing space, characterizing the microhabitat of a tree, including tree pit with or without a grille, irregular opening in the paved area, no opening (with concrete or asphalt paving up to the trunk base), planting strip, movable or fixed planter, and other types, Protection of growing space such as level or raised edges in relation to the surrounding ground surface and the presence or absence of enclosure, Guards or support such as tree guard, permanent or tem- porary tree stake or a similar structure, or no support, and Site dimension, recording the linear horizontal or vertical measurements shown in Figure 1, the number of traffic ©2008 International Society of Arboriculture Jim: Urban Forest Census in Hong Kong lanes perpendicular to the tree, and whether on-street car parking space was available adjacent to the tree; (4) Tree structure: Trunk girth, measuring at 1.3 m (4.3 ft) from the ground; if branching height was lower than 1.3 m (4.3 ft), the girth was measured immediately below the first branch; for multiple stemmed trees, the girths of the trunks were summed, Tree height using the trigonometric approach, Crown diameter measured by an electronic range finder; for evidently asymmetric crowns, the average of the maximum and minimum diameters was recorded, and Gap between crown and adjacent structure; if it was less than three-fourths of the crown diameter, the location of crown restriction (property, carriageway side, or both) was recorded; (5) Defects and disorders: Detailed evaluation of individual trees was made accord- ing to 33 common physical and physiological ailments placed under five groups, and Overall rating of tree performance, classifying a tree ac- cording to a 5-point scale (excellent, good, fair, poor, and dying); (6) Special features/remarks: Any unusual observation not solicited in the record form was recorded; and (7) Sketch: Where necessary, a simple sketch of the tree and its im- mediate environs was drawn to explain unusual obser- vations. Why Were Data on Potential Planting Sites Collected? The search for potential planting sites followed Table 2. Some attributes were similar to the tree survey, and only those unique to the site survey would be explained: (1) Basic information: Street number, referring to the starting and end point of the potential planting site, and Site code, a serial identification number; (2) Potential suitability: Site classification aided by a synoptic diagram of different roadside configuration vis-à-vis tree planting and growth potential, Width of the plantable corridor, which should be greater than 2 m (6.6 ft), and Roadside parking space, indicating opportunities to insert trees outside the curb line between the ends of parking spaces, where awning and other restrictions often did not allow planting inside the curb line; it could provide more room for tree crowns to expand above the car- riageway without causing unacceptable traffic or sight- line obstructions; (3) Site characteristics: The same attributes for the tree survey were recorded; (4) Growing space: Two attributes, namely roadside location and site dimen- sions, were recorded using the same format as the tree survey;
November 2008
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