380 Ning et al.: Assessing Urban Forest Structure and Health (1997), Miller (1997), Dwyer et al. (2000), and Nowak et al. (2002). Two major study methods were used, urban forest cover analysis and ground survey. Panchromatic aerial photographs (1:15,000 and 1:1,000) taken during the August 2001 flyover at a flying height of 1,500 m (4,950 ft) specifically made for this particular project were used for the urban forest cover analysis. Landsat TM5 satellite photographs from August 2001 were also used along with 1997 Landsat TM5 satellite photographs for comparison. The aerial photographs were scanned at 600 dpi and digitized manually at 1 m (3.3 ft) resolution to analyze the urban forest cover by using ArcGIS 8.1 (ESRI, New York, NY). The digitized map identified the five types/categories of urban forest cover. Field Plot Establishment The stratified random field sample plots were mapped and Figure 1. Map of the study area: central Shenyang. aggregated variable. Instead, the urban matrix should be catego- rized in subsystems because it is multidimensional and highly variable across space (Godefroid and Koedam 2007). Therefore, this assessment classified the urban forests in the study area into five types based on their function, location, land use type, distribution, benefits provided, and management ob- jectives. The five types are: 1. Landscape forest (L): trees located near and around build- ings for landscape purposes, including schoolyards, cam- puses, hospitals, commercial and business districts, indus- trial areas, and residential areas. The major functions are to beautify and improve people’s living and working en- vironments. 2. Road forest (R): trees along railroads, highways, boule- vards, roads, streets, and intersections and by bridges. The major functions are to protect the road, direct and regulate traffic, block traffic noise, and absorb traffic-related pollution. 3. Park forest (P): trees in public parks, forest parks, historic places, and scenic areas. The major functions are to provide recreation opportunities, sightseeing and vacation spots, locations for education and cultural activities, and to im- prove the environment. 4. Ecologic forest (E): trees and forests at the outskirts of the city planted as wind breaks, sand stabilizers, and pollution/ noise reducers; by water bodies such as rivers, dams, and lakes to protect watersheds and improve water quality; be- tween residential areas and industries to block pollution and noise; by levees to prevent flooding; and on slopes or adverse soils to prevent soil erosion. 5. Commercial forest (C): trees in nurseries, orchards, plan- tations, and woodlands for commercial purposes. The ma- jor functions are to provide seedlings and saplings for urban greening and reforestation, for fruit production, and for nontraditional forest products. Urban Forest Cover Analysis Study methods were derived from the urban forestry studies in the United States by Nowak (1992, 1994), McPherson et al. ©2008 International Society of Arboriculture evenly distributed based on the urban forest location, cover type, and size. An eTrex GPS (Garmin, Olathe, KS) unit by Garmin was used in the field to locate the plot sites. The total of 282 plots of three different sizes was established to ensure proper repre- sentation and coverage of all urban forest types. A 20 m × 20 m (66 ft × 66 ft) plot size was used in the parks, forest parks, scenic areas, and suburban areas, because the forests in these areas were relatively dense, resembled the naturally occurring forests, and were distributed in relatively large patches. A 40 m × 40 m (132 ft × 132 ft) plot size was used in areas such as school- yards, campuses, business districts, and residential areas, be- cause trees were scattered, separated by buildings, and not dis- tributed in large patches. A 20 m × 80 m (66 ft × 264 ft) plot size was used along railroads, highways, boulevards, and roads, be- cause trees are distributed along the roads; therefore, the plots were rectangular. Field Survey Data Collection Field survey data were collected from each plot and every tree and shrub in the plot. Data collected included plot number, date, location, land use type, species name, number of trees per spe- cies, tree diameter at breast height (dbh), and tree and shrub height. Tree dbh measurements were categorized into six classes: 0 to 10 cm (0 to 4 in), 10 to 20 cm (4 to 8 in), 20 to 30 cm (8 to 12 in), 30 to 40 cm (12 to 16 in), 40 to 50 cm (16 to 20 in), and larger than 50 cm (20 in). Height measurements were clas- sified into five classes: shorter than 3 m (9.9 ft), 3 to 5 m (9.9 to 16.5 ft), 5 to 10 m (16.5 to 33 ft), 10 to 15 m (33 to 49.5 ft), and taller than 15 m (49.5 ft). Health Condition Assessment Tree and shrub health condition data were collected during the field survey. Based on the tree condition assessment methods by the Council of Tree and Landscape Appraisers (2000), tree health was classified into five condition classes, which are 0, dead/dying; 1, poor/decline; 2, fair/average; 3, good/very good; and 4, excellent. Data Analysis Field data were entered into the computer according to the urban and suburban sectors and five major forest cover types. Diam- eter, height, and health condition distributions of urban and sub- urban trees and shrubs were obtained by assigning trees/shrubs into respective classes that are described in the previous two sections. Average diameter, height, and health condition index of
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