202 Cowett and Bassuk: Is Street Tree Diversity Increasing in New York State, USA? Separate statistics for population evenness (Buzas and Gibson 1969) were also calculated due to the importance of evenness in more fully understanding the diversity of tree populations. For example, even if Population A has a greater number of tree species and genera than Population B, if a sufficient number of the species or genera in Population A are represented by only a few trees, then the most prevalent species and genera in Population A can be more dominant than the most prevalent species and genera in Popula- tion B, and Population B would be more diverse. Table 2 summarizes these diversity statistics, which were calculated with PAST (PAleontological STatis- tics) software version 4.2 (Hammer et al. 2001). Comparisons were made between diversity statistics for the 75 inventories in this statewide assessment and those reported in the 2014 and 2017 statewide assessments (Cowett and Bassuk 2014; Cowett and Bassuk 2017). Statistics for evenness and effective diversity were not reported in the 2014 assessment, and statistics for effective diversity were not reported in the 2017 assessment, but these statistics were cal- culated from the data associated with those papers. For the 32 municipalities with multiple inventories, a diversity t-test (Hutcheson 1970) assessed the statisti- cal significance of change (P < 0.05) for Shannon- Wiener Diversity Index values between newer and older inventories. RESULTS Species and Genus Composition For this statewide assessment, Norway maple (Acer platanoides) was found to be the most prevalent street Table 2. Measures of tree species and genera diversity. Simpson Diversity Index (SDI) Simpson Diversity Index (SDI) οΏ½οΏ½ππκ²ηι― ππκ²ηι― ππκ²ηι― οΏ½ ππκ²ηι― Shannon-Wiener Diversity Index (H) Evenness Evenness Evenness Inverse SDI Inverse SDI Inverse SDI Effective diversity Effective diversity Effective diversity ππκ²ηι― οΏ½οΏ½ππκ²ηι― ππκ²ηι― ππκ²ηι― οΏ½ 2 2 Table 2. Measures of tree species and genera diversity. Table 2. Measures of tree species and genera diversity. Simpson Diversity Index (SDI) Shannon-Wiener Diversity Index (H) βοΏ½ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― eH/S eH/S eH 1/SDI eH eH /S 1/SDI 1/SDI eH Shannon-Wiener Diversity Index (H) βοΏ½ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― ππκ²ηι― where ni is number of individuals of taxon i where ni is number of individuals of taxon i where S is number of taxa where S is number of taxa where S is number of taxa where SDI is the Simpson index statistic where SDI is the Simpson index statistic where H is the Shannon-Wiener index statistic where ni is number of individuals of taxon i where ni is number of individuals of taxon i where ni individuals of taxon i where ni individuals of taxon i more sensitive to species and genera evenness is number of is number of more sensitive to species and genera evenness more sensitive to species and genera richness and to sample size more sensitive to species and genera richness and to sample size quantifies the similarity of species and genera frequencies quantifies the similarity of species and genera frequencies where H is the Shannon-Wiener index statistic where SDI is the Simpson index statistic not logarithmic, unlike the Shannon- where H is the Shannon-Wiener index statistic Wiener Diversity Index (H) and therefore more directly comparable Wiener Diversity Index (H) and therefore more directly comparable not logarithmic, unlike the Shannon- measures diversity rather than dominance measures diversity rather than dominance more sensitive to species and genera evenness more sensitive to species and genera richness and to sample size quantifies the similarity of species and genera frequencies measures diversity rather than dominance not logarithmic, unlike the Shannon- Wiener Diversity Index (H), and therefore more directly comparable tree species, with a weighted statewide percentage of 17.64% (21.38% unweighted), and maple (Acer spp.) was found to be the most prevalent street tree genus, with a weighted statewide percentage of 35.35% (41.82% unweighted)(Table 3). These findings are similar to those in the 2014 and 2017 statewide assessments in which Norway maple and maple were also found to be the most prevalent street tree species and genus (Cowett and Bassuk 2014; Cowett and Bassuk 2017). However, the percentage of Norway maple relative to all street tree species was found to be 14.58% less prevalent compared to its prevalence in 2014, and the percentage of maple relative to all street tree genera was found to be 19.90% less preva- lent compared to its prevalence in 2014 (Table 3). Sugar maple (Acer saccharum), silver maple (Acer saccharinum), and London planetree (Platanus Γ acerifolia) were street tree species also found to be less prevalent between this statewide assessment and the 2014 assessment, and planetree (Platanus spp.) and ash (Fraxinus spp.) were street tree genera also found to be less prevalent between this statewide assessment and the 2014 assessment. Conversely, honeylocust (Gleditsia triacanthos), Callery pear (Pyrus calleryana), crabapple (Malus spp.), and lit- tleleaf linden (Tilia cordata) were street tree species found to be more prevalent between this statewide assessment and the 2014 assessment, and oak (Quer- cus spp.), pear (Pyrus spp.), linden (Tilia spp.), and cherry (Prunus spp.) were street tree genera found to be more prevalent between this statewide assessment and the 2014 assessment. The 6 most prevalent street tree species statewide accounted for 43.19% of all street trees in this statewide assessment as compared Β©2021 International Society of Arboriculture
September 2021
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