Arboriculture & Urban Forestry 38(3): May 2012 89 Table 6. Canadian cities projected to show the greatest economic impact from EAB invasion over the next 30 years; ten cities are listed for each of three spread rates and two discount rates. Currency is expressed in Canadian dollars. Max. spread rate (km/year) 10 (slow) 0% Discount rate City Toronto Montréal Ottawa - Gatineau Québec Hamilton St. Catherines - Niagara Kitchener Windsor London Oshawa 30 (medium) Winnipeg Toronto Montréal Ottawa - Gatineau Québec Hamilton Brandon 50 (fast) St. Catherines - Niagara Kitchener Windsor Winnipeg Toronto Montréal Regina Ottawa - Gatineau Québec Moose Jaw Brandon Hamilton St. Catherines - Niagara Impact ($, millions) 96 95 27 23 20 15 13 10 10 8 161 97 93 27 25 20 16 15 13 10 172 96 92 53 27 25 23 22 20 15 dium and fast spread models are suggestive of potential benefits for slowing the spread of EAB. The difference in annual costs between the slow and medium spread rate models are between $6 million/year and $10 million/year (derived from the differ- ences in the annuity values shown in Table 5). Cost differences are of course higher for the slow versus fast rate models ($11– $18 million/year). Notably in slow rate models, western Canada has not been affected in the 30-year simulation period. Clearly the arbitrary cut-off of a 30-year time horizon does affect these results but with higher discount rates (e.g., 10%), this effect is lessened simply because of the strong effect of discounting over that length of time. At the 10% discount rate, the differences between the fast and slow spread rate models range from about $11 to $14 million/year ($3 to $7 million/year for the medium versus slow spread rate). Annual expenditures up to these lev- els to slow the spread of EAB would be justified on economic efficiency grounds if indeed they were judged to be effective. CONCLUSION EAB-related street tree damage was estimated in the study area over a 30-year time horizon to range from $265 million to $1,177 million depending on the combination of spread, treatment, and discount rates (~$451 million to $2,001 million with backyard trees included). Based on a medium spread rate, 10% treatment rate, and 4% discount rate, estimated costs were $524 million; this value increased to $891 million when costs were extended to include backyard trees. Cast in equivalent annual values, these estimates range from $18 million/year (2% discount rate, City Toronto Montréal Ottawa - Gatineau Hamilton St. Catherines - Niagara Kitchener Windsor London Québec Oshawa Toronto Montréal Winnipeg Ottawa - Gatineau Hamilton Québec St. Catherines - Niagara Kitchener Windsor London Toronto Winnipeg Montréal Ottawa - Gatineau Regina Hamilton Québec St. Catherines - Niagara Brandon Kitchener 4% Discount rate Impact ($, millions) 85 76 24 18 13 9 9 9 8 7 85 78 58 24 18 15 13 10 9 9 85 84 78 24 19 18 17 13 10 10 slow spread, and no treatments) to $45 million/year (10% dis- count rate, fast spread, and no treatments). Including backyard trees would increase these annual equivalents to ~$31 million and $77 million per year. Though conservative, these estimates are comparable to a similar study carried out in the U.S. (Ko- vacs et al. 2010), once differences in population size and study scope are taken into account. Community-specific cost esti- mates can be obtained by contacting the corresponding author. These findings can provide some justification for slow-the- spread initiatives, such as early detection surveys and wood movement laws. However, the net value of a slow-the-spread program depends on two major considerations: 1) the ex- tent to which it delays EAB arrival at a given urban centre, and 2) the perceived time value of expenditures as influenced by the discount rate. Nevertheless, even just the simple no- tion of preserving ash in communities for future generations may be an important consideration for some decisionmak- ers, especially if EAB proves to be as devastating as some be- lieve. Given the magnitude of the damage estimates provided here, there is also considerable economic justification for on- going research efforts to better understand and manage EAB. Acknowledgements. We thank: Irene Pines, Robert McMahon, and oth- ers at Manitoba Conservation for generously sharing their ash survey data; the Ontario Stewardship Rangers and all other volunteers who have helped to collect street tree data in eastern Canada; and Geoff McLeod, Bill Roe- sel, Jason Pollard, John McNeil, and Richard Ubbens for feedback on tree removal and replacement costs. We also thank two anonymous reviewers for their comments. Any errors remain the responsibility of the authors. ©2012 International Society of Arboriculture
May 2012
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