The following section highlights the findings generated from the CITYgreen analysis. The detailed results for each study site are included in Appendix B.
Forest Health
The CITYgreen analysis of forest health indicated that the trees at each study site were rated between “fair” and “good,” with an overall average health rating of 3.6 for all study sites, about halfway between “fair” and “good” (Table 3). Not surprisingly, the study sites with the lowest health rating (Downtown Business District and Downtown Neighborhood) were located in the highly developed urban areas of the city that are covered with large amounts of impervious surfaces. The highest health rating was found in the Young Neighborhood study site. Tree age is likely the biggest factor in determining a tree’s health, although additional factors likely played a role. For example, most trees in the Young Neighborhood site were relatively young and vigorous, having recently been planted after the development of the subdivision. By contrast, trees in the Downtown Neighborhood site had been established some time ago and were more mature and less vigorous.
Table 3 - Tree Health Ratings
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Study Site
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Tree Canopy (%)
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Average Health Rating1
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Apartment Complex
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15
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3.6
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Old Neighborhood
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36
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3.8
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Young Neighborhood
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7
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3.9
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Downtown Neighborhood
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21
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3.0
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Office Building
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14
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3.7
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Downtown Business District
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8
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3.3
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Average
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17
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3.6
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1 Health Class Rating
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1 - Dead/Dying
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2 - Poor
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3 - Fair
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4 - Good
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5 - Excellent
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Energy Savings
In the City of Macon, air conditioning costs represent a considerable expense to most residents, costing them about $600 a year to cool their homes. Analysis of data from the four residential study sites suggests that the existing tree canopy can save homeowners $16 to $69 in summer cooling costs. At this point, U.S. Forest Service research of energy savings from urban trees has only modeled the benefits provided to residential homes and not to commercial buildings. As a result, the energy savings for the two commercial study sites (Downtown Business District and Office Building) are estimations and are presented only to provide an approximation of the energy savings afforded to commercial buildings.
Not surprisingly, Table 4 indicates that the homes located in the study site having the greatest tree canopy cover (Old Neighborhood) had the highest energy and kilowatt hour (kWh) savings. However, significant tree canopy cover did not always correlate to large energy savings. For example, existing trees in the Young Neighborhood site are saving each homeowner about $39 a year. This site had the lowest canopy cover, seven percent, but had 16 percent of the existing trees in an energy rating class of three or better. By contrast, only ten percent the Downtown Neighborhood study site’s trees, with a canopy cover of 21 percent, were assigned to the three highest energy ratings. As a result, the greater canopy cover in the Downtown Neighborhood site produced lower energy and kWh savings than the Young Neighborhood site, largely because the existing trees in the Young Neighborhood site were planted in a way that afforded a greater energy savings.
Table 4 - Energy Savings
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Killowat Hour Savings
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Number of
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Tree
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Total
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kWh
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Study Site
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Buildings
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Canopy (%)
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kWh Savings1
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Savings / Home1
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Apartment Complex
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8
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15
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1671.0
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208.9
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Old Neighborhood
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9
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36
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7799.3
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866.6
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Young Neighborhood
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18
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7
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8729.3
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485.0
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Downtown Neighborhood
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28
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21
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9471.0
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338.3
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Office Building
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2
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14
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7800.0
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3900.0
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Downtown Business District
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10
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8
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5016.8
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501.7
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Average
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12.5
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17
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6747.88
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1050.06
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Dollar Savings
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Number of
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Tree
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Total
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Energy
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Study Site
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Buildings
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Canopy (%)
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Energy Savings ($$)
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Savings / Home ($$)
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Apartment Complex
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8
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15
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133.68
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16.71
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Old Neighborhood
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9
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36
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623.94
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69.33
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Young Neighborhood
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18
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7
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698.34
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38.80
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Downtown Neighborhood
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28
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21
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757.68
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27.06
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Office Building2
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2
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14
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624.00
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312.00
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Downtown Business District2
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10
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8
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401.34
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40.13
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Average
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12.5
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17
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539.83
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84.00
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1 Based on $0.08 per kilowatt hour (kWh) (Southern Company 2000).
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2 As USDA Forest Service research has thus far only modeled savings to residential buildings, the energy savings represented are estimates
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and are presented only to provide an approximation of the energy savings afforded to commercial buildings.
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