18 rates of ash decline in each forest at each survey date was determined by comparing observed and predicted numbers of ash trees entering at least the poor category with a Kolmogorov-Smirnov test (Gotelli and Ellison 2004). This method was also used to determine the ability of the model to pre- dict the number of ash trees removed in a city dur- ing the initial EAB invasion. Here, predicted values were compared with actual removals for the City of Fort Wayne, Indiana, from the first year EAB was detected (2006) through the year when the last of the 14,403 untreated ash trees were removed (2013). Modification of a Web-Based Cost Calculator The modified EAB Cost Calculator (Sadof 2016) is based on a previous version (Sadof et al. 2011) that used a local inventory of ash trees and local estimates of pricing for treatment, removal, and replacement of trees based on tree size. Users can choose predefined strategies or create their own strategy that chooses the percentage of trees in each size class that will be removed, replaced, or protected with insecticides. Annual and cumulative costs of up to three manage- ment strategies are plotted for 25 years. Benefits of each management strategy are compared by plotting the expected total dbh of all surviving ash trees re- sulting from each management strategy. To account for the time value of money, the modified calculator uses the same formula as in the first version to cal- culate the present value of costs (Rose et al. 1988). The local tree inventory is used to create a matrix of trees that is applied in an iterative approach to simulate annual tree growth and costs for 25 years. Trees within each size class are assigned equally spaced starting sizes that are approximated by divid- ing the span width by the number of trees in a size class. So, if there are 600 trees in the 15–30 cm cate- gory, the calculator creates a matrix of 600 trees with sizes 0.024 cm apart. Annual growth of surviving trees is approximated by a linear model that adds 1.143 cm of dbh per year based on a linear estimate of growth quantified for ash trees (Peper et al. 2014). When trees are “killed” by EAB or through planned removal, the model randomly selects individuals in each size class that will be removed and replaced. Two additional 15 cm growth spans are built into the model to receive trees that grow beyond the last size class provided by the original tree inventory. ©2017 International Society of Arboriculture Sadof et al.: Tools for Staging and Managing Emerald Ash Borer Cities whose trees have already begun to show damage can stage their infestation from the percentage of ash trees in the poor cat- egory and start the simulation at a more rel- evant point in the eight-year ash forest decline model. The EAB Cost Calculator allows cities to start as late as six-years into the invasion. By the seventh year of the cycle, when 64% of the trees are beyond saving, ash management options are restricted to removal and replace- ment. During this phase, the model’s predictions are not likely to be accurate because it cannot predict the distribution of live trees left to treat. Municipal arborists can adjust the frequency of pesticide applications to be most aggressive during the cusp and crest phases of the invasion as EAB populations are building and threaten- ing tree heath. Aſter 10 years, two years aſter all untreated trees are rendered beyond saving, there is little ash phloem to support the beetles. As such, populations of EAB are presumed to be present, but at a much lower level. For this reason, the EAB Cost Calculator switches from an aggres- sive to a maintenance phase of management aſter this time (Figure 1). Operationally, in the aggres- sive phase, all trees designated for protection are treated frequently enough to provide maximum protection. In the post-crest phase, pesticide applications are replaced by an integrated pest management approach that includes monitor- ing annually for fresh symptoms of EAB attack, such as woodpeckers or bark splits. Detection of these symptoms triggers a round of insecticide application, before substantial, additional canopy thinning occurs. Reduced costs are approximated in the model by reducing the frequency of pes- ticide application in this maintenance phase. Defining Management Strategies A fictitious forest, composed of 1,600 ash trees, was used to estimate management costs and forest growth over time (Table 2). The size class of this for- est was skewed toward larger trees to account for fewer ash trees being planted aſter EAB was detected in 2002. Approximately two thirds of the ash trees in this forest had a dbh > 30 cm. The costs of six com- mon management strategies (Table 3) represent a range of management combinations of tree removal, replacement, and treatment with insecticides.
January 2017
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