86 Sydnor et al.: Economic Impact Potential of Emerald Ash Borer (Agrilus planipennis) gregated results shown in Table 2 (within 5% and 3%, respec- tively, for mean- and median-based estimates of street trees; with- in 24% and 11%, respectively, for estimates of park trees; and within 11% and 14%, respectively, for estimates of private trees). To facilitate response, only the diameter of street trees was requested on the survey instrument. The average size of ash street trees reported by the communities was 33 cm DBH. To adjust for variations in size as reported by different communi- ties (Sydnor et al. 2007a), normalized dbh was calculated as 34 cm DBH and was used in subsequent cost calculations. One hundred and eleven communities reported the number of street trees in their community, as well as the percentage of ash trees, such that the number of ash street trees per 1,000 resi- dents could be calculated (Table 2). Minor skewness was seen with a mean of 60 ash trees per 1,000 residents and a median of 51.4 trees per 1,000 residents. When the mean and median numbers are adjusted to account for total population, estimates of the number of ash street trees in the four states were between 1,737,441 (median-based) and 2,028,141 (mean-based) trees. Fewer communities (n = 97) reported the number and percent- age of ash trees in their parks. Citizen advisory boards represent- ing communities are often charged with responsibility for street trees but not park trees and have even less responsibility for pri- vate trees. The reporting communities identified a mean of 29.9 ash trees per 1,000 residents and a median of 8.4 ash trees per 1,000 residents (Table 2). The amount of park land varies greatly among Midwest communities as does amounts of active and pas- sive parks, thus there was some skew evident in the distribution. Adjusting the mean and median to account for the four state to- tal population, estimates of the number of ash park trees were between 283,940 (median-based) and 1,010,690 (mean-based). Still fewer (n = 70) communities gave a complete response as to the number of trees on private property, thus impacting the estimate of the percent of ash on private property but within community boundaries. Several communities informed the study authors they were less comfortable in reporting private trees, as they did not keep records on private trees. As a result, a num- ber of communities did not report all of the requested data for private trees. The reporting communities had a mean of 331.7 private ash trees per 1,000 residents and a median of 156.1 pri- vate ash trees per 1,000 residents. Several follow-up calls were made regarding this category. It was discovered that the report- Table 2. Numbers of ash trees as street, park, and private trees per 1,000 residents as reported by the responding com- munities. Estimated total numbers of ash street, park, and pri- vate trees in four Midwest states adjusted for total population. Item 90% Confidence interval Number of Responses Four-state Tree Totals z (Median-based) Four-state Tree Totals y (Mean-based) z Mean-based totals = mean trees per 1,000 residents * (four-state popula- tion/1,000 residents) /1,000 residents) y ©2011 International Society of Arboriculture Street Tree Ash Median ash/1,000 residents 51.4 Mean/ 1,000 residents Standard deviation 60.0 52.4 51.7, 68.2 111 1,737,441 2,028,141 Park Ash 8.4 29.9 63.9 Private Ash 156.1 331.7 469.2 19.2, 40.7 238.2, 425.2 97 70 283,940 5,276,546 1,010,690 11,212,238 Median-based totals = median trees per 1,000 residents * (four-state population ing communities contacted were comfortable with their estimates and generally could explain their estimates and why their figures might have varied from more typical responses. When the mean and median numbers for private ash trees per 1,000 are adjusted upward for the four-state population, estimates of the numbers of private ash trees within the community boundaries were between 5,276,546 (median-based) and 11,212,238 (mean-based) trees. In order to get an estimate of the total impact of the poten- tial complete loss of native ashes, one should add the number of ash street trees, plus the number of ash park trees, and fi- nally the number of ash trees on private property per 1,000 resi- dents. The total of street, park, and private trees yields a mean of 421.6 ash trees per 1,000 residents and a median of 215.8 ash trees per 1,000 residents in the four-state region. This is a narrower spread than reported for Ohio (Sydnor et al. 2007a), where the mean-based estimate was 379.7 per 1,000 residents and the median-based estimate was 88.5. While the mean-based estimates were quite similar, the median-based estimate was higher in the present study, due mostly to higher figures for street and private ash. When adjusted for the region’s popula- tion this yields the total estimated number of ash trees within community boundaries in the four Midwestern states between 7.3 million (median-based) to 14.3 million (mean-based) trees. This is comparable to the estimate of 9.2 million ash trees in de- veloped areas within communities in the four Midwestern states reported by Kovacs et al. (2010). However, current estimates are less than that reported by Kovacs et al. (2010) for ash on all developed land (inside and outside community boundaries) of 25.7 million ash trees in the four-state region. As discussed later, the former (and similar) comparison is likely the most direct. Similar to the past study (Sydnor et al. 2007a), it was found that younger communities (average age of residential structures less than 60 years) were likely to have significantly more pri- vate ash trees per 1,000 residents than older communities (me- dians of 217.1 and 88.2, respectively; Wilcoxon rank sum test p = 0.05), and that larger communities (10,000 residents or more) tended to have more street ash per 1,000 residents than did smaller communities (medians of 52.7 and 33.3, respective- ly; p = 0.07). Thus, although the above figures for median- and mean-based total numbers of ash are not as widely dispersed as in previous studies (Sydnor et al. 2007a), younger and larger communities still might realize better estimates using the higher mean-based value, while older and smaller communities might realize better estimates using the lower median-based value, although these are generalizations and conditions will vary by community. For example, the tendency for younger communi- ties to have more private ash might be related to expansion of neighborhoods in city suburbs into second-growth forests or con- verted farmland where native ashes are common pioneer species. Potential Fiscal Impacts of the Complete Loss of Ash As described in Sydnor et al. (2007a), fiscal impacts of EAB on communities were expected to take three forms: landscape value of the existing tree that might be lost, the cost to remove the dead or declining tree, and replacement costs for a tree to replace the dead or damaged plant. The following analysis assumed the com- plete loss of all major native ash species in urban areas. Econom- ic impacts would be proportionately less if only a fraction of the
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