272 Dilley and Wolf: Homeowner Interactions with Residential Trees in Urban Areas place removed trees. The survey indicated that no district in the city is currently being reforested at this planting rate. Survey data were used to spatially align current canopy cover, planting po- tential, and reported future planting behaviors by district (Figure 3). Respondents in the West Seattle district expected to plant the greatest number of trees in the future (5.4 trees/acre on average) while respondents in Duwamish district expected to plant the fewest number of trees in the future (2.4 trees/acre on average). Responses to the attitude question, “Trees must be plant- ed and selected properly and I don’t know how” were also examined geographically. Positive responses (“agree” and “strongly agree”) were mapped by district (Figure 4) to visu- ally correlate with 2009 canopy cover and planting potential analysis. The district where the most respondents (32%) re- ported a lack of planting and selection knowledge was the area just west of the Duwamish River (in south Seattle). The lowest reported rate of planting and selection knowledge (8%) was in the Wallingford/Fremont district of north Se- attle. Areas of relatively low canopy cover and relatively high planting potential were of particular interest for the analysis. DISCUSSION This research addressed homeowner attitudes and behaviors in an effort to increase tree planting and retention across an entire urban area and boost canopy cover (and resulting ben- efits). Findings highlight the human dimension issues that ur- ban forest managers should consider when working to increase tree planting on single-family residential property, and sug- gest additional questions for future research. Findings of the current research on tree planting behavior are now informing the City’s delivery of tree programs and homeowner outreach. Tree Planting Behaviors Planting levels in Seattle may be slowing on single-family properties. It is unknown whether this is an isolated pattern, or consistent with other cities in the country. Regardless, Seattle’s urban forest managers are now aware that within limitations of self-reported predictions of future behavior, single-family residence canopy cover could decline without interventions, such as regulations, planting, or incentive programs. It is pos- sible that residents will plant more (or fewer) trees in the future than they believed they would at the time of the survey. Climate patterns differ across cities, affecting recommended planting seasons. Trees planted in autumn or winter have more time to establish root systems and survive the warm, dry sum- mers typical of the coastal Pacific Northwest region of the United States. Trees planted in the spring or summer are less likely to survive and thrive into maturity. The majority of Seattle’s home- owners are not planting at the recommended time. This may be partly due to local nursery practices that promote tree sales in the spring. In Seattle, and elsewhere, urban forest managers may need to encourage the retail nursery industry and homeown- ers to shift planting behavior to the most appropriate season. Respondents indicated a “downsizing” trend in species preference. Yet large trees provide greater environmental, social, and economic benefits than do small trees (McPherson et al. 2002; Wolf 2005; Sydnor and Subburayalu 2011). Ever- green trees, such as the large coniferous trees native in the Pacific Northwest, can intercept greater amounts of rainwater than deciduous trees (Xiao et al. 1998; Xiao et al. 2000; Link et al. 2004; Xiao and McPherson 2011), thus providing greater stormwater management benefits. However, suitable public planting locations for large trees are becoming less available in densely developed areas. Thus, working with homeown- ers through incentive programs or technical assistance to plant such trees on private property (e.g., in yards) may be one of the best ways to increase the number of large trees in urban areas. Solar Panels and Energy Demand Less than 10% of respondents indicated that their tree plant- ing decisions were influenced by the desire to maintain solar access for future panel installations. This attitude may Figure 3. Geographic distribution of homeowners’ expected future tree planting. Expected future tree planting is represented by the average number of future trees per acre on single-family residen- tial property across the city, calculated as the number of trees respondents reported to be considering planting in the future on average by district, times the number of single family parcels in each district, divided by the number of acres in each district. be more common in southern, sunnier cities. A more direct issue in the Seattle climate may be energy demand. There are a number of ways to reduce residential energy use, including less use of air conditioning. Seattle has mild summers, and few residents use home air conditioning. How- ever, in 2009 Seattle experienced record-breaking summer heat, with temperatures exceeding the previous high of 39.4°C (Mass 2009). If such heat trends continue, more residents may ©2013 International Society of Arboriculture
November 2013
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