54 Keto et al.: Urban Forest Characteristics in Raleigh Parking Lots Table 3. Pairwise comparison of composition among four classes of designed planting spaces, following significant one-way ANOVA. Islands have… Rows have… …than chunks No significant differences No significant differences Greater canopy per tree , (p = 0.0027) (rows = 37.6 m2 islands = 25.6m2 ), Greater mean basal area per tree (p = 0.0008) (rows = 0.07 m2 islands = 0.04 m2 ), Fewer trees per area (p = 0.0001) (rows = 200 trees per hectare, islands = 381 trees per hectare) Slivers have… Smaller mean tree height (p = 0.0019) (slivers = 5.0 m, chunks = 8.7 m) No significant differences Smaller mean tree height (p = 0.0024) (slivers = 5.0 m, rows = 8.2 m) Table 4. Pairwise comparison of composition among three types of preserved planting spaces following significant one-way ANOVA. …than chunks Islands have… Greater canopy per area (p < 0.0001) (islands = 321%, chunks = 109%), Greater basal area per area (p < 0.0001) (islands = 89.5 m2 chunks = 34.4 m2 per hectare, per hectare) Rows have… No significant differences. Less canopy per area (p = 0.0007) (rows = 155%, islands = 321%), Less basal area per area (p < 0.0001) (rows = 42.5 m2 islands = 89.5 m2 per hectare, per hectare) Table 5. Mean tree size by planting space type. All ranges are reported with 95% confidence. Designed Chunks Diameter (cm) Height (m) Canopy area (m2 ) 24.2 ± 2.3 8.4 ± 0.7 37.9 ± 7.0 Islands 20.1 ± 1.4 7.4 ± 0.4 24.5 ± 4.2 Rows 24.8 ± 1.1 8.5 ± 0.3 38.3 ± 3.3 mia indica) was the most common non-native species, and is estimated to represent almost half of non-native trees. DISCUSSION Raleigh’s parking lots can contain tens of thousands of trees representing many different species. While the high variability in the data allows only a rough estimate of the overall number of parking lot trees in the study area, the methods used should provide more precise information if re- sources allow a larger portion of the population to be sampled. The composition of trees in Raleigh’s parking lots was correlated with the size, shape, and origin of the plant- ing spaces within the lots, but not with the size or shape of the parking lots themselves. This correlation does not im- ply that these factors cause trees to grow faster, or reach larg- er sizes, nor does this snapshot study distinguish the effects ©2012 International Society of Arboriculture Slivers 14.6 ± 4.4 5.2 ± 1.3 12.3 ± 13 Preserved Chunks 12.0 ± 1.4 8.1 ± 0.6 7.7 ± 1.8 Islands 22.7 ± 7.6 11.7 ± 3.4 21.4 ± 10.0 Rows 20.8 ± 2.1 11.4 ± 0.9 17.4 ± 2.8 of these factors from others, such as tree age and species, owner preferences, soil properties, or maintenance practices. Preserving versus Planting Trees in Parking Lots There were clear differences between preserved and designed planting spaces. Preserved spaces were dominated by upland species, while planted spaces contain mostly bottomland spe- cies. If compared to an upland piedmont hardwood forest, a representative hectare of preserved planting spaces would be stocked at more than 110% (47.8 m2 trees per hectare), while a representative hectare of designed planting spaces would be only 60% stocked (13.3 m2 basal area per ha/ 809 basal area per ha, 334 trees per hectare) (U.S. Forest Service 1999). Some preserved spaces contained a very high density of small diameter trees that can block lines of sight and decrease area aesthetics, they may therefore warrant thinning (Anderson …than islands X , X …than islands X …than rows X
March 2012
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