Arboriculture & Urban Forestry 41(6): November 2015 present value of benefits nearly equal to the costs of removing ash trees as they die (benefit-cost ratio of 1.02). However, the net value of remaining trees aſter a 20-year period in the do-nothing scenario ranged from USD $868 (using i-Tree Streets to value the benefits of trees) to $44,913 (using CTLA appraisal methods to assess tree values; VanNatta et al. 2012). This was compared to the best-case scenario (based on CTLA appraisal values) of treat- ing all trees (scenario 4; yielding $84,610 net value remaining aſter 20 years; VanNatta et al. 2012). The economic analyses of EAB detailed here have yielded tools available for managers fac- ing decisions about managing EAB. These tools include the EAB Calculator (Sadof et al. 2011; Purdue 2015) and the EAB PLANning Simulator (VanNatta et al. 2012; UWSP 2015), both of which allow urban forest managers to calculate costs of different control methods for emerald ash borer. Integrated pest management Integrated pest management (IPM) and monitor- ing of pest and disease populations rose in promi- nence for urban areas in the late-1970s as a means of reducing the risk of economically damaging pest outbreaks in urban areas and the costs of control- ling outbreaks. IPM methods are not unique to urban forestry and arboriculture but originated in the field of agriculture to monitor and manage crop pests. In 1978, Olkowski and Olkowski introduced the idea of an urban IPM to arborists as a means of more effectively dealing with the diversity of vegetation pests found in cities and to enable cost- effective dissemination of practices to homeowners. These authors introduced the concept of injury level, or the level of pest infestation (in number of insects per unit of vegetation; e.g., leaf area) at which damage to the tree is unacceptable and treat- ment of the pest becomes desirable (Olkowski and Olkowski 1978). Establishing injury levels for urban pests and trees helps minimize application of pesticides (i.e., costs of pesticide use) and make effective use of limited resources for treating pests in the urban forest (Olkowski and Olkowski 1978). Ball and Marsan (1991) advocated for the estab- lishment of an action threshold, as the level of pest infestation or incidence just below the injury level at which economic or aesthetic thresholds are reached, and at which treatment should begin. In economic 309 terms, the economic injury level occurs at the point at which the marginal benefits obtained when trees are treated for a pest (i.e., the increased benefits due to prolonged tree lifespan) equal the marginal costs of the treatment (i.e., the dollars and time spent treating trees). An aesthetic action threshold is a management approach with treatment meant to avoid surpassing an unacceptable injury level, which is a point that vitality is reduced detrimen- tally. Subsequent authors have encouraged proac- tive monitoring (including visual inspection of trees for damage and pest incidence, locating vulnerable populations of trees, trapping and baiting of pests, and monitoring of environmental conditions suit- able for specific pests or for pest outbreaks; Raupp 1985; Ball 1987), preventative maintenance (to pro- mote tree health; Nielsen 1986), and minimizing periods of tree stress to reduce susceptibility to pest or disease infestation (Moorman 1985). Reardon et al. (1987) provided a description of implementing an IPM program to control gypsy moth infestation (although results of the program are not provid- ed). However, beyond statements asserting that IPM and monitoring practices are economical, no authors advocating IPM provide explicit informa- tion about its costs or compare costs to traditional management of pest populations with pesticides. Maintenance Not Commonly Quantified in Municipal Budgets Some types of tree maintenance are much less completely quantified and studied. The costs as- sociated with risk management, watering, mulch- ing, soil and nutrient management, staking, tree support systems (e.g., cabling, bracing, and prop- ping), and protection during construction are less explicit in literature from the field of arboriculture and urban forestry. These tend to be tasks that do not earn line items in city budgets, and so do not appear as clearly quantified in records. These types of maintenance may occur less systematically across a population of trees in the urban forest, and may be more likely borne by a nonprofit organization, neighborhood, or citizen in charge of tree care. Tree risk management One of these less-studied costs of not maintaining trees is related to tree risk and liability management. If a lack of maintenance results in a tree that fails ©2015 International Society of Arboriculture
November 2015
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