Arboriculture & Urban Forestry 40(3): May 2014 Table 3. Comparison of tree health condition between the SFASU campus and the city parks. Condition class SFASU campus Trunk (1–5) Growth (1–3) Crown structure (1–5) Insects/Diseases (1–3) Crown development (1–5) Life expectancy (1–5) Total (0%–100%) average rating (SD) 4.0 (1.3) 2.7 (0.7) 3.7 (1.4) 2.6 (0.7) 3.4 (1.3) 4.1 (1.2) 78% (0.2) Service’s Evaluation of Texas Shade Trees, a dollar value was Based on the Texas Agriculture Extension calculated for each tree. When using $75 as the International Society of Arboriculture (ISA) value per square inch of cross-sectional area, the total value of all trees on SFASU campus (n = 3,345) was over $27 million ($27,251,104) with individual val- ues ranging from $0 (dead trees) to $89,780, which was a Quercus virginiana. The average value of the campus trees was $8,179. If all the trees were in perfect condition (assume condi- tion value as 1.0), the total dollar value would be more than $35 million ($35,018,000) for all campus trees, which is more than $8 mil- lion difference from the current condition. For city park trees, the total value of the 1,572 trees was $20,735,279 based on unit value of $75. Values ranged from $0 (dead tree) to $79,317, which was a Quercus nigra located in Oak Grove Cemetery. The average value of the city park trees was $13,190. If all were in optimum condition (referred to as perfect by Dreesen 1994)—26 out of 26—the total dollar value would increase to $28,848,824. The use of the CTLA method incorpo- rates the evaluator’s expertise in evaluation of the physical tree characteristics and how these charac- teristics affect value. The CTLA method integrates valuation with readily available tree parameters, location, and species information (Cullen 2007). Trees evaluated in excellent condition could have minor leaf or needle defoliation or discoloration that did not diminish the overall quality. While there is no perfect tree, evaluators need to take into consideration the impact of biotic and abiotic influences on the tree in its location, species, and condition. When the two groups were compared, SFASU campus trees had lower average value than those of the city parks, although campus trees had a greater total value due to its larger population. City park average rating (SD) 3.6 (1.0) 2.5 (0.7) 3.3 (1.0) 2.2 (0.7) 3.4 (1.0) 3.6 (1.0) 72% (0.2) P-value of t-test <0.0001 <0.0001 <0.0001 <0.0001 0.4324 <0.0001 <0.0001 171 Better condition Campus Campus Campus Campus N/A Campus Campus Table 4. Comparison of biodiversity between the SFASU campus trees and the city park trees. Total (N) Richness (S) Simpson’s Index of Diversity 1 – D Simpson’s Reciprocal Index 1 / D SFASU campus City parks 3,335 72 Shannon–Wiener Index of Diversity (H) 2.6 Species Pielou’s Evenness (H/lns) Simpson’s Index D 0.6 0.2 0.8 4.6 1,572 45 2.9 0.7 0.1 0.9 12.1 The Shannon–Wiener index (H) for SFASU campus trees and city park trees resulted in close values with city park tree (2.9) slightly greater than SFASU campus trees (2.6) (Table 4). For the 3,335 measured SFASU campus trees, there were 79 species with an Evenness value of 0.6 calculated. For the city park trees (n = 1,572), species Richness is 44 and Evenness 0.7. Although the species Richness at SFASU campus is higher than in city parks, all the Simpson’s index values indicated greater diversity in city parks, which is in agreement with the Shannon–Wiener’s index result. However, Simpson’s index gives more weight to the more abundant species in a sample. Although rich and diverse in species, trees in the study area are unevenly distributed. The popula- tion on SFASU campus tree is dominated by Pinus taeda. Some city parks are dominated by a single species, such as Carya illinoinensis in Pecan Park. That is not desirable for tree management and dis- ease control, and will negatively affect tree health. Spatial analysis applied to the SFASU main campus and the three largest city parks, Pecan Park, Maroney Park, and Pioneer Park, sepa- rated trees within each area into two geographic groups, Center and Edge. The results showed that trees growing on the edge had a better health con- dition than trees located at the center for both Pioneer Park (P = 0.038) and the SFASU campus (P < 0.0001). No significant difference was found for Pecan Park and Maroney Park (Table 5). ©2014 International Society of Arboriculture
May 2014
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