74 Sadof et al.: Restoration Capacity and Costs of Managing the Emerald Ash Borer in Urban Forests Arboriculture & Urban Forestry 2011. 37(2): 74–83 Evaluating Restoration Capacity and Costs of Managing the Emerald Ash Borer with a Web-based Cost Calculator in Urban Forests Clifford S. Sadof, Lindsey Purcell, Forrest J. Bishop, Carlos Quesada, and Zhi-Wei Zhang Abstract. Described here is the development of a web-based cost calculator for projecting management costs and restoration, during a planned response to an emerald ash borer invasion in the City of Indianapolis, IN, U.S. Forest sizes, measured as the sum of tree diameters, and costs of managing urban ash trees were projected under various management scenarios over a 25-year period. The study authors illustrate how a city can use local information to compare management plans. Although the simple strategy of treating all ash trees provided the lowest annual cost and produced the largest forest, this option was ultimately the most expensive. Simply removing ash trees and replacing them with resistant trees restored the forest to its initial size after 25 years. However, after taking five years to complete tree removal and replacement, the initial ash for- est was reduced to a mere 27% of its original size. When this management plan was modified, by protecting trees in the median size class with insecticides, the restoration forest was below 50% of the initial size for two years but at a discounted cost that was only 6% greater than replac- ing all trees. The authors of the study describe how the cost calculator can be used to address the unique local attributes of urban forests. Key Words. Emerald Ash Borer; Forest Restoration; Management Costs. Emerald ash borer (EAB), Agrilus planipennis, is a highly ag- gressive metallic wood boring beetle that attacks and kills oth- erwise healthy ash trees in the genus Fraxinus (Cappaert et al. 2005). Adult females lay eggs in cracks and crevices of tree bark that hatch into larvae which bore beneath the bark to feed on and destroy phloem and other adjacent vascular tissues. Ash trees native to North America are particularly susceptible to beetle attack (Anulewicz et al. 2008). Since its detection in 2002 near Detroit, MI, U.S., it has now been reported in 15 U.S. states and two Canadian provinces (Cappaert et al. 2005). EAB spreads by both natural and artificial means (Poland and McCullough 2006). In the presence of abundant hosts, natural spread from a colonization site is less than 400 m/yr (Mercader et al. 2009). In southeast Michigan, movement of infested ash material including nursery stock, firewood, and ash debris dra- matically increased the rate of spread to 20 km/yr (Siegert et al. 2007). Prasad et al. (2010) found that outlier infestations are often located in the vicinity of highways, further empha- sizing human-aided dispersal in long-distance spread of EAB. As a significant component of the urban forest canopy, ash trees provide substantial benefits to cities (McPherson et al. 2006). Approximately 38 million ash trees are estimated to be in urban areas located in 25 states in the northeastern United States surrounding the initial Detroit detection (Kovacs et al. 2010). Spread of emerald ash borer is expected to affect nearly 17 million urban trees in this area from 2009–2019. The dis- counted cost in today’s dollars of removing, replacing, and protecting these trees with insecticides during this 10-year pe- riod is predicted to be USD $10.7 billion (Kovacs et al. 2010). ©2011 International Society of Arboriculture Individual ash trees can be protected with repeated applica- tions of systemic insecticides that diffuse toxicant from their ring porous xylem to leaves where the insecticide kills adults (Mota-Sanchez et al. 2009). The ability of an insecticide to dif- fuse through the tree in sufficient concentration to kill beetles is influenced by its solubility, toxicity, dose, application meth- od, the infestation status, and the size of the tree (Herms et al. 2009; Smitley et al. 2010). Trees with most of their functional xylem intact have the best chance of taking up and distribut- ing the insecticide. Trees whose canopies have been thinned by more than 50% from a combination of EAB infestation and other stressors are not likely to be saved by insecticide application. Longevity of protection provided by a single insecticide appli- cation ranges from one to three years and depends on the com- pound, dose, and the solubility of the insecticide formulation. Benefits and costs of removing and treating trees with insec- ticide are driven by tree size (McPherson et al. 2006, McPherson 2007; Herms et al. 2009). This study includes a report on the development of a web-based tool called the Emerald Ash Borer Cost Calculator (Sadof 2009a), which uses a size class based tree inventory to project forest size, costs of insecticide treatment, and removal and replacement of ash trees over a 25-year period from local bids for any combination of these strategies. Using the City of Indianapolis, IN, U.S. as a case study, the study authors demonstrate how output from the calculator can be used with lo- cal information to discuss tradeoffs between costs and reforesta- tion during the development of a community EAB response plan.
March 2011
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