Arboriculture & Urban Forestry 38(4): July 2012 Arboriculture & Urban Forestry 2012. 38(4): 121–129 121 To Treat or Remove: An Economic Model to Assist in Deciding the Fate of Ash Trees Threatened by Emerald Ash Borer Daniel W. McKenney and John H. Pedlar Abstract. A model is presented to assist in deciding the fate of ash trees (Fraxinus spp.) threatened by the arrival of emerald ash borer (Agri- lus planipennis Fairmaire) in North America. The model tracks ongoing treatment costs versus one-time costs associated with removal and re- placement. All future values are discounted following standard economic practice. For each year over a period of interest, the net treatment gain/ loss is calculated, indicating the period of time over which a homeowner would be financially ahead/behind by treating the existing ash tree. The model was populated, with values that may be expected in Canadian conditions, where treatment options are more limited than in the United States. Optional model features include property value premiums, energy savings, runoff and pollution benefits, and ongoing maintenance costs. When these extended benefits and costs are included, positive treatment gains for a medium-sized ash persist for about 17 years. Negative val- ues can be interpreted as a “break-even existence value,” an amount a homeowner would be required to pay in order to protect their ash if vari- ous other benefit flows fail to compensate the costs. An interactive version of the model is available online (http://gmaps.nrcan.gc.ca/apm/index.php). Key Words. Agrilus planipennis; Canadian Forest Service Ash Protection Model: CFS-APM; Cost-benefit Analysis; Emerald Ash Borer; Insecticide Treatments; Urban Forest Management To treat or not to treat? That is the question facing many North American ash owners since the arrival of the emerald ash borer (EAB) from Asia (Cappaert et al. 2005). The larvae of EAB feed on the phloem and xylem of ash trees, eventual- ly cutting off the flow of nutrients and usually killing the tree within fives years of initial attack (Siegert et al. 2007). All North American ash species (Fraxinus spp.) can be attacked, although blue ash (Fraxinus quadrangulata Michx.) and Asian ash species appear less susceptible (Anulewicz et al. 2007). Presented here is a model that assists users (such as home- owners, arborists, and consulting foresters) in deciding whether to treat or remove ash trees threatened by EAB. The model works by tracking, through time, the costs and benefits asso- ciated with treating a tree versus removing and replacing it. Sadof et al. (2011) present a useful web-based ‘EAB cost cal- culator,’ which serves a similar general function to the model presented here. However, the approach here differs in a num- ber of ways, including the incorporation of a wider range of tree-related costs and benefits. The model is applied in a Ca- nadian context but the model, at least in its simplest form, is general enough to be applied elsewhere. Decisions to protect tree assets can be complex, involving relatively straightfor- ward financial considerations, such as treatment, removal, and replacement costs, as well as more subtle factors, like the influence of tree cover on property values, home energy bud- gets, and even what economists may term as “existence” val- ues (Krutilla 1967; Boardman et al. 2001), where homeowners may simply “like” the existence of tree cover on their prop- erty and are willing to pay for the pleasure of such enjoyment. Since being discovered in southern Michigan in 2002, EAB has spread rapidly across eastern North America (Prasad et al. 2010). In Canada, the outbreak currently includes much of southern Ontario; major centers such as Toronto, Montreal and Ottawa; and isolated infestations as far north as Sault Ste. Marie, Ontario (Canadian Food Inspection Agency 2010). Over time, EAB is expected to continue its spread across Canada and the United States, decimating ash in both natural and urban settings along the way. Kovacs et al. (2010) estimate the cost to municipalities in the northeastern United States to be $10.7 billion over the next decade (see also Sydnor et al. 2011). McKenney et al. (2012) estimate the cost in Canadian mu- nicipalities to be upwards of $2 billion over the next three decades for street and backyard trees depending on spread and treatment rates. Given its extensive foothold in North America, it is highly un- likely that EAB will be eradicated, although efforts are ongoing to identify effective biological control agents (e.g., Yang et al. 2010). One option available to property owners is to protect ash trees against EAB attack using insecticide treatments that would be re- quired on an ongoing basis. A variety of products have been test- ed for this purpose (Herms et al. 2009; McKenzie et al. 2010). In Canada, at the time of writing, three products were registered by Canada’s Pest Management Regulatory Agency for use in con- trolling EAB: TreeAzin™ , ACECAP® 97, and Confidor® 200 SL. For the current work, the use of the model was illustrated by us- ing treatment costs and application frequencies associated with TreeAzin. This is a systemic insecticide (injected into the trunk of trees) produced from extracts of Neem tree (Azadirachta indi- ca) seeds, which has shown promise in controlling both the lar- val and egg stages of the EAB life cycle (McKenzie et al. 2010). ©2012 International Society of Arboriculture
July 2012
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