308 Vogt et al.: The Costs of Maintaining and Not Maintaining the Urban Forest ment scenario consisting of two inspections per year, prompt removal of infected trees, and deadwood pruning of all trees yielded the highest benefit-cost ratio of the examined alternatives (Sherwood and Betters 1981). These authors also provided a step- by-step method for assessing the benefits and costs of alternative DED management programs for a municipality considering undertaking DED control (Sherwood and Betters 1981). Other authors over the years have examined the biological costs (e.g., mor- tality of trees, development of fungicide-resistant DED strains) of DED control and treatment efforts without matching economic data to treatment options (Wilson 1976; Campana 1977; Gregory and Allison 1979; Sherald and Gregory 1980). Economics of other pests Studies examining the economics of pest manage- ment include Dreistadt and Dehlsten (1986; costs of aphid honeydew pest management), Jetter et al. (1997; costs of ash whitefly biological control), Ko- vacs et al. [2010; economic damage potential of the emerald ash borer (EAB), Agrilus planipennis], and VanNatta et al. (2012; cost of EAB management). Dreistadt and Dahlsten (1986) described a study undertaken to determine the costs of aphid hon- eydew pest management for tuliptrees (Lirioden- dron tulipifera) compared to removal and replace- ment of diseased trees. Costs of pest management were estimated as direct costs by city arborists and parks supervisors and included structural and clear- ance trimming, removal and replacement of 1% of trees each year, and sidewalk repair and modi- fications necessitated by tuliptree trunk growth (Dreistadt and Dahlsten 1986). Removal and re- placement of 400 tuliptrees with London plane- trees (Platanus acerifolia) was only 63% of the cost of continued maintenance of the tuilptrees (USD $223,000 compared to $354,000 in 1984$; Dreis- tadt and Dahlsten 1986). Costs excluded from this analysis include potential liability costs, tempo- rarily lost aesthetic value, and other tree benefits. Jetter et al. (1997) performed a benefit-cost analysis of the use of a parasitic wasp (Encarsia inaron) to biologically control the ash whitefly (Siphoninus phillyreae), which attacks ash (Fraxinus spp.) and ornamental pear (Pyrus spp.) trees. They compared the change in appraised value due to pest dam- age (benefits) to the costs incurred by the entities ©2015 International Society of Arboriculture conducting the biological control (including per- sonnel, travel expenses, and materials; Jetter et al. 1997). Given total program costs of only USD $2.0 million ($1.2 million in 1992$), total net benefits of the program were almost $536 million whole- sale ($323 million in 1992$) and $682 million retail ($411 million in 1992$) for street trees only (Jet- ter et al. 1997). In other words, if biological control efforts had not occurred, over a half billion dollars in street tree appraisal value would have been lost. Current pest threat: Emerald ash borer Kovacs et al. (2010) examined the costs that will be incurred for municipalities as a result of emerald ash borer damage in municipalities in a 25-state region centered on Detroit, Michigan, U.S. (the epicen- ter of North America’s EAB infestation), between 2009 and 2019. Using simulations of the spread of EAB and costs of various treatment options or removal and replacement for trees of different sizes, the authors estimated the costs of EAB man- agement (Kovacs et al. 2010). The analysis assumed that homeowners and tree managers act optimally and “[maximize] the present value of a stream of benefits and costs associated with each tree by choosing among four actions—1) do nothing, 2) remove, 3) remove and replace, or 4) treat with an insecticide that prevents injury from EAB” (Ko- vacs et al. 2010, p. 573). They concluded that EAB will cost U.S. communities an estimated $11.4 bil- lion ($10.7 billion in 2010$) in discounted terms between 2009 and 2019 (Kovacs et al. 2010). Note that the Kovacs et al. (2010) scenario was an optimal one, assuming completely rational actors acting op- timally in the face of EAB infestation, and does not allow for calculation of the costs of doing nothing. VanNatta et al. (2012) provided more detailed EAB management scenarios based on the projected management costs and tree value. They simulated the costs of four management scenarios for the ash tree population on the University of Wisconsin– Stevens Point campus: 1) doing nothing and removing ash trees as they die; 2) immediately removing all ash trees over a five-year period; 3) immediately removing and replacing ash trees with non-ash trees; and 4) minimizing mortality by treating all ash trees with approved insecticide treatments (VanNatta et al. 2012). The costs of doing noth- ing to combat EAB (scenario 1) yielded an annual
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