Arboriculture & Urban Forestry 40(5): September 2014 ment management costs by protecting paving from weathering (McPherson and Muchnick 299 2005). Also, there is growing evidence that trees provide public health benefits. Tree loss from emerald ash borer (Agrilus planipennis) has been correlated with increased mortality related to cardiovascular and lower-respiratory-tract illness (Donovan et al. 2013). Although emerald ash borer is an emerg- ing threat in California, the polyphagous shot hole borer (Euwallacea sp.) and gold-spotted oak borer (Agrilus auroguttatus) are present in the Los Angeles region and pose grave threats to the urban forest, with potentially adverse impacts on human health. This study did not quantify MTLA program costs, which include planning, site prepara- tion, tree production and planting, stewardship (e.g., irrigation, pruning), monitoring, outreach, and administration. Future research is needed to calculate MTLA’s net benefits, as well as envi- ronmental impacts at each stage of its life cycle. CONCLUSIONS In the eight years aſter Mayor Villaraigosa launched MTLA, 407,000 trees were planted and the pro- gram is now part of the green fabric of Los Angeles, California. Although the 91,786 trees planted from 2006 to 2010 is substantially less than the targeted one million, findings from this study indicate that survivorship over the first five years exceeded rates reported for comparable cities. Moreover, sampled MTLA trees are growing at rates typi- cal for the same species in Claremont, California, and trees in other subtropical urban forests. This study’s projected amounts of CO2 stored, avoided emissions and co-benefits per tree planted exceeded estimates from the initial assessment. One reason is that MTLA is planting large-stature trees in greater proportion than their distribution as vacant planting sites (30% versus 9%). Also, avoided CO2 emissions from energy savings were substantial for both street and yard trees, indicating that they are being selected and located for building shade. Park tree plantings were projected to store the most CO2 per tree planted because 80% were medium- and large-stature species and survival rates were high. Although MTLA planted less than one-half of its ambitious target, it would be short-sighted to call the program a failure for this reason alone. Many more trees were planted than were being planted previously. Most importantly, these early results suggest that MTLA is achieving a high level of suc- cess in terms of tree survival, growth, and benefits produced. Continued success will depend on raising awareness of proper tree care practices, strategi- cally selecting and locating new trees, monitoring threats, and adapting to the challenges that arise. As the MTLA program enters a new chapter of its life, it has an opportunity to lead others by renew- ing its focus on sustaining the trees that it plants. Acknowledgments. I am deeply indebted to the many partners who assisted with this study. Los Angeles Conservation Corp’s Meghan Shearer led field data collection, while Dan Knapp pro- vided tree planting information. MTLA staff Lisa Sarno, Elizabeth Skrzat, Melinda Bartlett, and Thalia Uribe shared their database and described their program. George Gonzalez and Ron Lorenzen (LA Bureau of Street Services) as well as Laura Baurenfeind and Leon Boroditsky (LA Recreation and Parks Department) generously out- lined their programs’ specific tree planting and stewardship activities. Ryan Allen (TreePeople) shared data on park tree planting and sur- vival rates. Drs. James R. Simpson, Lara Roman, and Alissa Kendall (UC Davis), Paula Peper and Shannon Albers (USDA Forest Service, PSW Research Station) provided technical support during portions of the study. LITERATURE CITED Aguaron, E., and E.G. McPherson. 2012. Comparison of methods for estimating carbon dioxide storage by Sacramento’s urban forest. pp. 43–71. In: R. Lal and B. Augustin (Eds.). Carbon Sequestration in Urban Ecosystems. Springer. Dordrecht, Netherlands. California Air Resources Board. 2011. Compliance Offset Protocol: Urban Forest Projects. California Air Resources Board. Sacra- mento, California, U.S. 44 pp. Condon, P., and S. Moriarty. 1999. Second Nature: Adapting LAs Landscape for Sustainable Living. TreePeople, Los Angeles, California, U.S. 116 pp. Donovan, G.H., D.T. Butry, Y.L. Michael, J.P. Prestemon, A.M. Liebhold, D. Gatziolis, and M.Y. Mao. 2013. The relationship between trees and human health: Evidence from the spread of the emerald ash borer. American Journal of Preventive Medi- cine 44:139–145. Escobedo, F., S. Varela, M. Zhao, J.E. Wagner, and W. Zipperer. 2010. Analyzing the efficacy of subtropical urban forests in off- setting carbon emissions from cities. Environmental Science & Policy 13:362–372. Hildebrandt, E.W., and M. Sarkovich. 1998. Assessing the cost- effectiveness of SMUD’s Environment 32:85-94. shade tree program. Atmospheric Hymon, S., and J. Merl. 2006. L.A. to be remade in the shade. October 1, 2006. Accessed 10/10 /2013. Jo, H.K., and E.G. McPherson. 1995. Carbon storage and flux in urban residential greenspace. Journal of Environmental Man- agement 45:109–133. Jones and Stokes Associates. 1998. Cost-Benefit Analysis for the T.R.E.E.S. Project: Product Specification for Transagency Re- ©2014 International Society of Arboriculture
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