Arboriculture & Urban Forestry 41(6): November 2015 between tree planting and the last positive point at which carbon sequestration no longer exceeded carbon emission (Nowak et al. 2002). Kendall and McPherson (2012) present a life cycle assessment that measures the greenhouse gas emissions of tree production. In the assessment, they consider all sources of emissions, including those associated with maintenance activities at the nursery, such as materials needed for staking, or nutrients used to amend soil (Kendall and McPherson 2012). In a similar analysis, McHale et al. (2007) investigate the carbon footprint of tree planting initiatives in the context of carbon credit markets. This article sum- marizes application of a set of guidelines for calcu- lating carbon emissions and reductions associated with urban tree plantings to Colorado, U.S. cities to assess the cost effectiveness of tree planting in the carbon trading market (McHale et al. 2007). Main- tenance is considered in two parts of their analysis: 1) in terms of emissions generated by “tree care activities” and 2) in total monetary costs of planting and maintenance over a 40-year time frame (“how oſten the trees are watered, pruned, or fertilized, and whether or not volunteers are involved in these processes”) (McHale et al. 2007, p. 52). However, as maintenance rates were fixed and were not examined as part of the analysis performed with either Kendall and McPherson (2012) or McHale et al. (2007), researchers cannot compare estimates of emissions costs between maintenance scenarios. Other authors have examined the costs of urban greenspace more generally using a life cycle approach (e.g., Jo and McPherson 1995; Jo 2002; Strohbach et al. 2012). Costs not considered in current literature Some costs of urban trees are largely ignored in the current literature. Commonly omitted costs include those incurred for leaf collection and the release of biogenic volatile organic compounds into the atmosphere. Where BVOC release is in- cluded as a “cost,” it is usually included in the estimation of air pollution or emissions reductions rather than itemized as its own cost (e.g., McPher- son et al. 2006). Pollen release from trees may exacerbate costs of allergies and medical treatments. A final important omitted cost is the opportunity cost of alternative land uses for the tree planting location. When trees are planted in the public right- of-way, the space cannot be used for other things, 299 such as an outdoor café, a bike lane, parking, or ad- ditional lanes of traffic (Loukaitou-Sideris 2011). Assessing the costs of not maintaining trees Ryan (1985) was one of the only authors to explicitly mention the costs of not maintaining trees in light of municipal tree budgets: “. . . trees that are not maintained at regular intervals soon become haz- ards due to deadwood and windthrow. This cannot only upset your budget but may also cause consider- able loss of life and property” (p. 114). In the paper, Ryan presented a dialectic for construction of a mu- nicipal tree maintenance budget and claims that both the “Estimated Cost of NOT Doing Tree Work” (emphasis original) and the “Estimated Savings by Doing Work” are important parts of justifying bud- gets (Ryan 1985). However, this article provides no specific suggestions for how to estimate these costs. Ryan (1985) argued that urban trees should be con- sidered part of urban infrastructure (as what is, in modern terms, “green,” or living, infrastructure, to contrast with grey infrastructure, such as roads and sewer systems), and uses this idea to describe how the benefits of trees can be used to help justify costs of city tree budgets. In a related article pub- lished in the Journal of Arboriculture, Schwarz and Wagar (1987) asked, “how much should you spend now [on street tree maintenance] to save later?” These authors presented three accounting frame- works that can be used to determine when preven- tative maintenance can result in decreased overall tree maintenance costs (Schwarz and Wagar 1987). However, the methods presented (discounted pres- ent value of future benefits, internal rate of return, and service-life extension value or useful-life value) require that maintenance needs in the future be es- timated (Schwarz and Wagar 1987), and the article did not provide guidance on how exactly to predict maintenance needs or estimate what they might cost; the authors also choose a discount rate that has large impacts on the conclusions of the study. Maintenance Commonly Included in Municipal Budgets Costs of trees are frequently expressed in terms of expenditures by the parties who commonly pay for the care of trees. O’Bryan et al. (2007) estimated that the private arboriculture industry (excluding munic- ipalities, nonprofits, or other non-commercial firms, ©2015 International Society of Arboriculture
November 2015
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