218 Hwang et al.: Tree Planting Configuration Influences Shade on Residential Structures al. 2010), regional guidelines published by uni- versity extension programs focus solely on the associated state. Therefore, university extension guidelines tend to be more specific. For example, the Minnesota guidelines recommend a specific tree direction (either east or west), distance (6 m away), as well as tree form (large canopied tree at least 3 m higher than window), with which simula- tions of the current study agree. Even though all guidelines affirm that trees on the west aspect are the best option for shade tree planting, they oſten do not fully address the interaction between tree form, tree placement, and geographic latitude. The simulations show that regional tree plant- ing guidelines recommending planting a shade tree on the east or west aspect of a dwelling for energy conservation are appropriate. Trees on these aspects have been found to provide abundant shade during the cooling season while simultaneously minimiz- ing unwanted shade during the heating season. In contrast, shade trees placed on the southern aspects are shown to do the opposite. Southerly-placed trees cast a lot of undesirable shade in the heating sea- son, yet provide minimal shade during the cooling season. Therefore, planting guidelines are correct in restricting or attaching conditions for planting a tree on the south aspect. For example, a common recommendation to minimize the heating pen- alty of tree shade (especially in northern latitudes) is to plant a “solar-friendly tree”—a deciduous, high-crowned tree, which allows sunlight to pass under the tree and reach the structure during the heating season (McPherson et al. 2005; McPher- son et al. 2006; Peper et al. 2009; Peper et al. 2010). While planting guidelines tend to correctly recommended cardinal tree orientation around a dwelling, they oſten do not stress the impor- tant interaction between tree form and tree dis- tance, which were found through simulations to have significant impacts that should be addressed for optimal tree planting strategies. For example, the Community Tree Guides (Table 1) recommend planting a tree at a distance between 9 and 15 m in order to provide effective shade on windows and walls as well as to avoid tree conflicts to the struc- ture (McPherson et al. 2005; McPherson et al. 2006; Peper et al. 2009; Peper et al. 2010). Avoiding con- flicts between a tree and a structure is an impor- tant aspect of a sustainable landscape; however, the ©2015 International Society of Arboriculture simulation results indicated that shade provision on building surfaces noticeably decreased when placed more than five meters away from the structure. The simulations also showed that at all latitudes shade provision was reduced even more drastically with distance as the tree size decreased. This effect was evident particularly in northern latitudes when considering the average shade provision during the cooling season (Table 4). For example, in Minneap- olis, with a large deciduous tree (15.2 m tall) situated at five meters on the west aspect, average shade pro- vision was valued at 419 m2 at 10 m, and 210 m2 , but reduced to 303 m2 uous tree (7.3 m tall) placed at five meters on the west provided average shade provision of 114 m2 but reduced 46 m2 at 10 m, and 18 m2 at 15 m. Likewise, a small decid- , at 15 m. Shade simulations showed recommendations for distance associated with tree sizes. Large trees (15.2 m tall) were less influenced by an increase in distance from the structure than medium (11 m tall) and small (7.3 m tall) trees. Large trees were shown to provide increased tree shade (exceeding the 75th percentile of all estimates over the entire year) at distances from 5 to 15 m. On the other hand, it is recommended to plant a medium tree within 10 m or a small tree within 5 m away in order to acquire tree shade greater than 112 m2 (the 75th percentile) during the cooling season. In comparison to trees on either east or west aspects, due to higher sun angles, south-positioned trees are more sensi- tive to an increase in distance from the structure; regardless of tree size these trees should be placed close to the structure for tree shade to ensure adequate shade during peak cooling season while also minimizing the winter season heating penalty. Across the study areas, the simulations sup- port planting a shade tree on either the east or west aspect as the best option for energy conserva- tion. However, when planting on the east or west aspect is not an option, the recommendation for shade tree selection and placement will depend on the latitude and climate. In northern latitudes (Minneapolis and Indianapolis) with longer heat- ing seasons, trees on the southeast or southwest aspect would be the second-best option. Trees on these aspects provide constant tree shade through- out the year, casting more shade in the cooling season and less in the heating season than a south- positioned tree. In these northern latitudes, the
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