Arboriculture & Urban Forestry 33(1): January 2007 5 can be observed. Although in this example, benefit-based estimates of value were less than cost-based estimates, a more complete accounting of tree benefits will narrow this gap. Research that identifies, quantifies, and monetizes other ben- efits such as effects of trees on human health and well-being and on the vitality of commercial areas is critical to future application of benefit-based valuation (see Social Aspects of Urban Forestry Special Issue, Journal of Arboriculture, May 2003). The benefit-based approach is similar to the cost-based approach in that tree species and location are important terms that can be explicitly defined. The same green ash tree lo- cated opposite a south-facing wall would produce less energy savings and associated air quality benefits than the tree op- posite a west-facing wall. This difference is easily obtained with the benefit-based approach, and is considered, although less directly, in the cost-based calculations in the terms for placement and contribution rating. Tree condition is directly included in the cost-based method but not used in the benefit-based approach. This is an important limitation because the production of current and future benefits should be directly linked to tree health as well as tree size. As currently calculated, green ash benefits reflect the dimensions and health of the Fort Collins sample street tree population on which this study was based, not any single tree. Another limitation to estimating the future stream of benefits with the benefit-based approach is uncertainty as to tree longevity. Published data on the typical lifespans of trees in different regions and growing conditions are scarce. Nev- ertheless, several tree valuation approaches do include life expectancy (Watson 2002, Randrup 2005). Particularly in cities outside the United States, multistory buildings may contain retail commercial uses at ground level and residential uses above. Benefits produced by a tree in front of the building can influence several property owners in different ways depending on the types of heating and cooling equipment, energy use patterns, and property values. This issue is under investigation in Lisbon, Portugal. METHODS—MULTITREE EXAMPLE This real-world example involves five Chinese pistache (Pis- tacia chinensis) street trees planted 15 years ago (1990) along Antelope Drive in Davis, California. It asks three questions: 1. How do cost-based estimates of tree value compare with benefit-based estimates? 2. Using the benefit-based approach, can we determine if it is cost-effective to remove and replace these trees in a more suitable site nearby? 3. Using the benefit-based approach, can we determine how much money would have been saved if the trees had been planted in the better site originally? Figure 4. Streetside location of the five pistache trees as well as the shrub bed to the right where replanting was considered. Tree number 5 is closest to the camera sta- tion. ©2007 International Society of Arboriculture Cost Approach The five trees were measured and appraised following pro- cedures outlined in the Guide for Plant Appraisal (Council of Tree & Landscape Appraisers 2000) with advice from Dr. Richard Harris (University of California, Davis), who has led development of this approach. The trees were located in a quiet, residential neighborhood adjacent to a parking lot for condominium units and across from single-family houses (Figure 4). The trees were located in a 46 to 92 cm (18.4 to 36.8 in) strip between the mountable curb and sidewalk. They did not appear to be irrigated, although excess irrigation could run into the planting strip from the shrub bed across the sidewalk. The trees were of similar size (dbh ranging from 21 to 25 cm [8.4 to 10 in]) and condition (48% to 64%; Table 2) with the exception of tree 5, which exhibited symptoms of stress. Location ratings were the same for each tree: 80%, 70%, and 50% for site, contribution, and placement, resulting in an overall location rating of 67%. The location rating re- flected the attractive and relatively high market value of the area, the important functional and aesthetic contributions of the pistache trees on this residential street, and their unfavor- able placement in a narrow strip that limited tree growth, led to curb and sidewalk damage, and increased tree and infra- structure management costs. A species rating of 90% for Chinese pistache was obtained from data for the Northern California Interior Valley in the Regional Supplement (WC-ISA 2004). The unit cost for the largest transplantable tree (24 in box, $173) was $11.94/cm2 TA ($77.04/in2) and the installed cost was $345 per tree. Benefit Approach In this example, the future streams of benefits and costs are estimated and net benefits are calculated by subtracting total
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