AnalysisCost of potential emerald ash borer damage in U.S. communities, 2009–2019
Introduction
Emerald ash borer (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), a phloem-feeding beetle native to Asia, was discovered near Detroit, Michigan and Windsor, Ontario in the summer of 2002. Increased awareness of emerald ash borer (EAB) and ongoing survey efforts have led to the detection of numerous EAB populations throughout Michigan, Ohio and Indiana. Estimates indicate that more than 53 million native ash (Fraxinus sp.) trees had been killed by EAB in those states by 2007 (Smith et al., submitted for publication). By March 2009, EAB infestations had been found in a total of ten states and two Canadian provinces (Fig. 1).
Emerald ash borer has the potential to spread and kill ash trees throughout the United States. Much of the damage caused by EAB occurs on developed land since ash trees have been a popular street tree for decades. The low genetic diversity of planted ash in the cities of the United States, predominantly white and green ash (F. americana, F. pennsylvanica), enhances the risk to the urban forest resource (MacFarlane and Meyer, 2005). Most EAB in North America develop in a year, although at very low densities some larvae require two years to develop (Tluczek et al., 2008). Adult beetles feed on small patches of ash foliage from late May through September and cause negligible damage. Individual eggs are laid on the bark of ash trees at least 5 cm in diameter at breast height (1.4 m above ground) and hatch in 1–2 wks. Larvae feed under the bark on phloem and cambium, typically from mid summer through fall. Larval galleries effectively girdle the phloem and score the outer sapwood, disrupting nutrient and water transport within the tree (Cappaert et al., 2005). As EAB densities build over time, tree health declines until the tree dies.
Trees with low densities of larvae typically exhibit few or no external symptoms (McCullough et al., 2009) and infestations are rarely discovered before canopy dieback or tree mortality occurs. Intensive analysis of trees in localized outlier sites has indicated that trees typically must be infested by EAB for 3–4 years before they succumb (Siegert et al., 2006). Flight mill studies indicate that mated females may be physiologically able to fly 5 km (Taylor et al., 2006); however, most adults fly less than 100 m when ash trees are near. Long distance dispersal of EAB can also occur when humans inadvertently transport infested ash nursery trees, logs, firewood or related material. Because visual detection of eggs, larvae, and adult beetles is difficult, multiple cohorts are likely to have dispersed before the first sign of infestation is detected.
In response to the threat posed by EAB, federal, state and provincial agencies impose quarantines to restrict the movement of ash from infested counties, conduct surveys to detect new infestations, and support research on EAB biology and management. These programs are expensive, yet there is little economic literature on the cost of EAB management and loss from EAB damage, especially in developed areas. In one example, Sydnor et al. (2007) estimates EAB could result in the removal and replacement costs of $1.0–$4.2 billion in Ohio communities. Assessing the potential economic impacts of EAB is important for evaluating the benefits of efforts to slow the range expansion of EAB, as well as investments in research on EAB biology and management. To help address this gap, we estimate the discounted cost of ash treatment, removal, and replacement in communities in a 25-state study area centered on Detroit (Fig. 1) by simulating EAB infestation over the next decade (2009–2019) and calculating the costs associated with ash treatment, removal, and replacement.
Our estimate of the discounted cost of treatment, removal, and replacement in response to EAB infestation over the 10-yr horizon, $10.7 billion, indicates nearly $1 billion per year in tree treatment, removal, and replacement costs.1 Additional investments could include continued enforcement of quarantines to restrict transport movement of ash material, surveys to detect new infestations, and outreach to increase public awareness. Enhanced investments in research on effective control, containment and management strategies, survey methodology and related avenues that could slow EAB expansion are also warranted.
Section snippets
Methods
The study area (Fig. 1) includes 25 states that we predict will have EAB infestations by 2019. The next decade (2009–2019) was chosen for our analysis because this is a logical time frame for the purpose of planning a policy response to the EAB invasion. Projecting the EAB infestation and costs further than a decade would require assumptions that are difficult to justify. Our approach to estimate the discounted cost of ash treatment, removal, and replacement has three primary components. First,
Results
We estimate that 37.9 million ash trees grow on developed land within communities in the study area (Table 5), ranging from 42,000 ash trees in Delaware to 5.5 million ash trees in Illinois. The state with the largest ash population (Illinois) has a large amount of canopy cover on developed land (47,460 ha) and high ash density (289 trees per ha cover). Our estimate of the number of ash trees on developed land in Minnesota communities (1.8 million) is comparable to a recent estimate made by the
Conclusions
Our estimate of the discounted cost of treatment, removal, and replacement in response to EAB infestation over a 10-yr horizon from 2009–2019 is $10.7 billion. Since the cost of treating, removing, and replacing all the 37.9 million ash trees on developed land in communities at once is $25 billion, this indicates a justification for substantial investment to slow the spread of EAB and postpone treatment, removal, and replacement costs if feasible. These investments could include continued
Acknowledgement
The authors are grateful to David Nowak and Eric Greenfield for sharing digital maps of U.S. Census-defined communities and data for 2001 NLCD developed areas and tree cover. Anne Cumming, Douglas Moore, David Nowak, Amelia Nuding, Lindsey Purcell, Noel Schneeberger, David Sivyer, Eric Smith, and T. Davis Sydnor provided tree inventory information for cities and regions. This work was conducted as part of the Ecological and Economic Impacts of Non-native Forest Pests and Pathogens in North
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