Arboriculture & Urban Forestry 47(5): September 2021 207 Table 7. Correlations for Inverse SDI (Inverse of Simpson’s Diversity Index), Shannon-Wiener Diversity Index, effective diversity (eH Species ), and evenness with relative abundance percentages for prevalent street tree species and genera (Pearson’s R, P < 0.05). eH Inverse SDI Statewide/2020 Norway maple London planetree Pin oak Multiple inventories/newer Norway maple London planetree Japanese tree lilac Genus Statewide/2020 Maple Oak Cherry Multiple inventories/newer Maple Oak Cherry −0.9341 0.5277 0.4584 −0.9130 0.5521 0.4294 the newer and older inventories yield findings similar to the statewide findings, with 12 years on average between the inventories. Therefore, between the state- wide assessments and the municipalities with multi- ple inventories, it does appear that the percentages of Norway, sugar, and silver maples relative to other street tree species and the percentage of maples rela- tive to other street tree genera have declined in New York State. Moreover, for the municipalities with multiple inventories, the number of Norway, sugar, and silver maple street trees declined, as did maple street trees more generally, while the overall number of street trees increased. Statewide statistics for the Inverse SDI, the Shannon- Wiener Diversity Index, and effective diversity indi- cate that the values calculated from the inventories obtained for this statewide assessment are greater than the values calculated from the inventories asso- ciated with the 2014 and 2017 statewide assessments (Cowett and Bassuk 2014; Cowett and Bassuk 2017). For some of the same reasons applicable to the state- wide relative abundance percentages, caution should be exercised in characterizing these findings as increases. However, for the municipalities with mul- tiple inventories, values for the Inverse SDI, the −0.9134 0.4111 0.3154 −0.8635 0.3067 0.2208 −0.8875 0.6330 0.4855 −0.8172 0.6814 0.4486 −0.6290 0.5316 0.4378 −0.5087 0.5232 0.3829 Shannon-Wiener Diversity Index, and effective diver- sity are greater for the newer inventories than for the older inventories. Therefore, between the statewide assessments and the municipalities with multiple inven- tories, it does appear that diversity values for street tree species and genera have increased in New York State. Given that Norway maple and maple are the most prevalent street tree species and genus, and that their relative abundance percentages were found to be negatively correlated with statistics for the Inverse SDI, the Shannon-Wiener Diversity Index, and effec- tive diversity (Table 7), it is reasonable to attribute at least part of the increase in diversity values to the decline in the percentages of Norway maple relative to other street tree species and to the decline in maple relative to other street tree genera. However, the mixed results for evenness (Table 6), particularly at the species level, where some diversity statistics were found to be correlated more with the number of spe- cies and genera than with the evenness of the species or genera distribution, suggest that, although there have been increases in the number of street tree species and genera in street tree populations (Table 5), these increases do not represent sufficiently large numbers of trees. As a result, Norway maple continues to be ©2021 International Society of Arboriculture −0.7842 0.2384 0.2371 −0.6992 0.2544 0.1247 Shannon-Wiener_H −0.7579 −0.0956 −0.1409 −0.6847 −0.1813 0.2026 −0.6671 0.2046 0.2067 −0.5363 0.2006 0.2281 −0.5250 0.2202 0.1867 −0.4461 0.2128 0.0853 Evenness
September 2021
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