Arboriculture & Urban Forestry 41(3): May 2015 other species, where species in the original forest once grew, has greatly increased. Evergreen gym- nosperms, none present in presettlement India- napolis, with the possible exception of redcedar (Juniperus virginiana), comprise 10% of street trees. These data show that human preference has greatly altered the tree composition of Indianapo- lis. Shiſts in dominance from native species, such as oaks, to smaller-statured, shorter-lived non- native species have been reported for the urban forests of Chicago, with associated loss of ecosys- tem service over time predicted (Fahey et al. 2012). The Future The non-profit beautification group Keep In- dianapolis Beautiful (KIB) is partnering with the city to plant 100,000 trees. The choice of species planted will be the greatest opportunity humans have to directly influence the future of Marion County’s urban tree composition. Records of re- cent plantings show native trees are the most com- monly selected, with over 20% of 12,174 trees planted since 2008 being species of oaks (Table 3). Oaks have declined in the county since preset- tlement times. Species of depressional ponds and seasonally flooded wetlands, like swamp white oak (Quercus bicolor) and bur oak (Q. macrocarpa), have had their habitats drained. Oaks planted in urban spaces will replace an all but lost component of the native forest, providing wildlife with food and habitat. Oaks in the eastern United States provide significant ecological services as one of the best food sources for birds and other desirable wild- life that feed on insects (Burghardt et al. 2009). Although slightly more than 20% of trees planted by KIB are oaks, no single species com- prises more than 10% of the total. For sustain- ability in an urban forest, Santamour (1990) recommends no single species should be more than 10% of trees planted in a given area, and no genus more than 20%. KIB’s planting list also follows the recommendation of Peper et al. (2008), for Indianapolis to plant non-maples. Natural forces that will continue to influence forest composition on a landscape scale include additional introduced pests. The emerald ash borer (Agrilus planipennis Fairmaire) (EAB), a coleopteran beetle, was recently introduced and is spreading in the county (Purdue Univ. Exten- 143 sion 2015). Ashes have declined from approxi- mately 12% of all trees in historical surveys, to around 3% in recent surveys, before the arrival of the EAB. It is predicted all untreated trees will die. Ashes comprise about 7% of street trees. Streetscape tree selection is influenced by many factors, including availability, price, aes- thetics, species’ viability in the urban environ- ment, and cost of maintenance. To the extent native species can be chosen while weighing these factors, urban trees can increase biodi- versity of associated flora and fauna (Ikin et al. 2012) in cities while promoting regional distinctness and countering biotic homog- enization. However, a caveat looking into the more distant future, is that as tree spe- cies distributions are shifted by global climate change, historical species composition may become less relevant as baseline condition data. Table 3. Trees planted in Indianapolis by Keep India- napolis Beautiful (2008–2011). Species Quercus macrocarpa Quercus bicolor Cercis canadensis Amelanchier × grandiflora Quercus rubra Quercus muehlenbergii Gymnocladus dioicus Liquidambar styraciflua Juniperus virginiana Acer saccharum Ulmus americana Nyssa sylvatica Acer rubrum Amelanchier sp. Quercus sp. Common name Bur oak Swamp white oak Redbud Serviceberry Red oak Chinquapin oak Kentucky coffeetree Sweetgum Redcedar Sugar maple American elm Black gum Red maple Qty. 774 745 592 520 416 415 407 387 383 377 368 336 323 Serviceberry species 319 Oak species 255 CONCLUDING REMARKS With an estimated annual loss of urban tree cover, a proxy for overall urban forest resources, of 0.9% in the United States (Nowak and Greenfield 2012), threats to urban trees continue. Informa- tion on how urban forests are changing is needed to better inform policies to “protect, sustain and enhance urban forests health and benefits for future generations” (Peper et al. 2008). Although it does not include data for trees in backyards or other private property (those data do not exist for Indianapolis and likely never will due to property owners’ rights), this study provides a snapshot of tree composition in Indianapolis, al- lowing a degree of quantification of the current ©2015 International Society of Arboriculture % total 6.4 6.1 4.9 4.3 3.4 3.4 3.3 3.2 3.1 3.1 3.0 2.8 2.7 2.6 2.1
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