300 Vogt et al.: The Costs of Maintaining and Not Maintaining the Urban Forest and excluding utility arboriculture) collected nearly USD $9 billion in gross receipts in 2002 (although this analysis is unable to disaggregate this figure into types of tree care or maintenance). Municipality expenditures on maintenance are more easily dis- aggregated by type: the most well-established types of tree maintenance activities—planting, pruning, removal, infrastructure repair, and pest/disease management—frequently appear as line items in city budgets (Kielbaso et al. 1982; Kielbaso 1990; Tschantz and Sacamano 1994; Kenney and Idziak 2000), while items like watering and mulching appear far less frequently (e.g., Thompson et al. 1994). Municipal costs are also commonly reported in benefit-cost analyses (studies that compare the costs and benefits of urban forests (e.g., McPher- son et al. 1997; McPherson et al. 1999; Maco and McPherson 2003; McPherson 2003; McPherson et al. 2005; Millward and Sabir 2010; Roy et al. 2012). For example, McPherson (2003) reported on the size-specific maintenance costs for plant- ing, pruning, removal, root-related infrastructure repair, pest management, and liability associ- ated with 10 species of street trees in Modesto, California, U.S. (results reproduced in Figure 5). Surveys of municipalities in the United States (400 municipalities: Kielbaso et al. 1982; 1,534 munici- palities: Kielbaso 1990; 419 municipalities: Tschantz and Sacamano 1994), in Canada (92 municipalities: Kenney and Idziak 2000), and in Santiago, Chile (Escobedo et al. 2006) have reported on the total tree-related expenditures of municipal governments. In the United States, tree expenses were distributed among street trees (61%) and park trees (24%; Kiel- baso et al. 1982), and as a whole accounted for less than one-half of one percent of total city budgets (Kielbaso 1990). Average annual per-capita munici- pal tree expenditures in the United State were $7.70 in 1974 ($1.63 in 1974$; Kielbaso 1990), $6.19 in 1980 ($2.19 in 1980$; Kielbaso et al. 1982), and $5.53 in 1986 ($2.60 in 1986$; Kielbaso 1990). Annual per-tree expenditures were $30.48 in 1980$ ($10.78 in 1980$; Kielbaso et al. 1982) and $22.57 ($10.62 in 1986$; Kielbaso 1990). Kenney and Idziak (2000) conducted a survey of Canadian municipalities between 1996 and 1998 and reported that average expenditures on tree maintenance were CAD $3.00 per capita and CAD $23.55 per tree annually ($2.20 and $17.29, respectively, in 1997$). Escobedo et al. ©2015 International Society of Arboriculture (2006) report results of expenditures by Santiago’s regional government on “green area management,” finding that municipality-level spending varied from $27,366 to $1,628,304 ($16,000 to $952,000 in 1991$) per year, while per-tree maintenance costs ranged from $0.17 to $6.84 ($0.10 to $4.00 in 1991$). Figure 5. Tree value increases as the size of trees increase (top). The cost of tree maintenance varies by life stage of tree and maintenance requirement (bottom). Figure reprinted from McPherson (2003). Pruning Of all urban forest maintenance activities, prun- ing is the most studied in terms of economics. Pruning is performed throughout the lifetime of a tree for various reasons, including: improving growth form (Evans and Klett 1985; Ryder and Moore 2013); alleviating structural problems, such as removal of deadwood (Hensley 1979); crown raising (Clark and Matheny 2010); and manag-
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