168 Kulhavy et al.: Comparison of Tree Condition and Value in Texas, U.S. or more trees were observed. Data were analyzed using Statistical Analysis Soſtware (SAS) version 9.1 (SAS Institute, Cary, North Carolina, U.S.). Biodiversity The Shannon–Wiener index and Simpson in- dex were calculated and compared to ana- lyze the biodiversity for each park and for the SFASU campus. The Shannon–Wiener index was calculated based on the following formula: total sample belonging to ith [3] where H’ = index of diversity, and pi H’ = ∑ (pi ) (ln pi ) = proportion of species. The species bio- diversity including evenness and richness were ana- lyzed based on the result of Shannon–Wiener index. Simpson’s index D measures the probability that two individuals randomly selected from a sample will belong to the same species, and was calculated based on the following formula: [4] D = ∑ − N N n n ( ( 1) − 1) where n = the total number of organisms of a par- ticular species and N = the total number of organ- isms of all species. With this index, 0 represents infinite diversity and 1 indicates no diversity. That is, the bigger the value of D, the lower the diversity. This is neither intuitive nor logical. In order to get over this problem, D is oſten subtracted from 1 to derive the value of Simpson’s Index of Diver- sity: 1 – D. This index also ranges between 0 and almost 1. In this case, the greater the value is, the greater the diversity. Another derivative is Simp- son’s Reciprocal Index: 1 / D, which starts with 1 as the lowest possible value representing a com- munity having only one species. For this study, all the three indices—Simpson’s index D, Simpson’s index 1 – D, and Simpson’s index 1 / D—were cal- culated. Higher values represent greater diversity. Spatial Analysis Within the Spatial Statistics toolbox in ArcGIS 10.1, the Mean Center and Standard Distance tool were used to identify the geographic center for trees and the core area in each park and the campus. On the output, the center of the trees in a study area was located and the standard distance circle was drawn ©2014 International Society of Arboriculture to identify the core of the study area. This core area assisted in separating trees into two geographic groups: center trees and edge trees. A t-test (alpha 0.05) on tree health condition was conducted to see if there was any significant difference be- tween the two groups of trees in each study area. RESULTS For SFASU campus, a total of 3,335 trees were mea- sured and 79 species identified. The most abundant species was Pinus taeda (loblolly pine) with 1,508 trees. Other abundant species included Quercus nigra (water oak, 180 trees), Lagerstroemia indica (crapemyrtle, 158 trees), Liquidambar styraciflua (sweetgum, 148 trees), and Pinus echinata (short- leaf pine, 122 trees). Thirteen of the 79 species were identified as having more than 50 individuals, and 59 of the 79 species were less than 30 individuals. For city park trees, a total of 1,572 trees were mea- sured in 26 city parks and cemeteries with 44 species identified. Carya illinoinensis (pecan) was the most abundant species with 292 trees. Other abundant species included Pinus echinata (shortleaf pine, 159 trees), Quercus virginiana (live oak, 153 trees), and Pinus taeda (loblolly pine, 131 trees). Thirty-two of the total 44 species had less than 30 individual trees. For the tree species with more than 30 individu- als, the health condition ratings for the SFASU cam- pus trees were significantly greater than the city park trees (Table 1), indicating they were healthier. Among the twelve species, only three species (Pinus echinata, Quercus stellata, and Ulmus americana) did not differ between SFASU and park trees (P > 0.05). The campus tree species with the highest overall condition rating of 89% was Q. virginiana and the park tree species was 77% for Q. stellata. The campus tree species with the lowest overall condition rating of 68% was P. echinata and the park tree species was 63% for Q. nigra (Table 1). The condition variables (trunk, growth, struc- ture, disease and insect, crown development, and life expectancy) were compared for SFASU campus and city park trees (Table 2). Celtis laevigata, Pinus taeda, Ulmus alata, and Liquidambar styraciflua of campus trees compared to park trees were sig- nificantly higher in all condition variables except crown development. Juniperus virginiana campus trees were significantly higher in all variables except growth and crown development. For Pinus echinata,
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