286 McPherson: Monitoring Million Trees LA Arboriculture & Urban Forestry 2014. 40(5): 286–301 Monitoring Million Trees LA: Tree Performance During the Early Years and Future Benefits By E. Gregory McPherson emissions (27.7 kg), rainfall interception (1.5 m3 Abstract. Million Trees LA (MTLA) is one of several large-scale mayoral tree planting initiatives in the United States, striving to create more livable cities through urban forestry. This study combined field sampling of tree survival and growth with numerical modeling of future benefits to assess performance of MTLA plantings. From 2006 to 2010 MTLA planted a diverse mix of 91,786 trees. Survivorship rates of 79.8%, 90.7%, and 77.1% for street, park and yard trees were relatively high compared to other studies. Growth rates averaged 0.99 and 1.1 cm DBH per year for street and yard trees. They were similar to rates for the same species in Claremont, California, U.S., and trees in other subtropical urban forests. Projected over 40 years, the amounts of CO2 stored per tree planted per year (20.1 kg), avoided ), and air conditioning savings (47.4 kWh) exceeded estimates from a previous assess- ment. One reason is that MTLA has planted more larger-stature trees than anticipated. Avoided CO2 emissions from energy savings were (42.0 kg per tree per year) because of their large-stature and high survival rate. Although MTLA has not reached its goal of planting 1 million trees, early results suggest that it is achieving success in terms of tree survival, growth, and performance. Continued success will depend on proper tree care practices, strategically selecting and locating new trees, monitoring threats, and adapting to challenges that arise. Key Words. California; Carbon Monitoring; Park; Planting; Sequestration; Street Trees; Tree Growth and Mortality; Tree Planting Ini- tiatives; Urban Forestry; Yard. relatively large because trees were judiciously located for building shade. Park tree plantings were projected to store the most CO2 Antonio Villaraigosa became mayor of the City of Los Angeles on July 1, 2005. The following day he planted a tree to announce his plan to plant one million trees, saying, “Los Angeles, the dirtiest big city in America, has the opportunity to be the greenest” (Hymon and Merl 2006). The ambitious tree initiative was called Million Trees LA (MTLA). Eight years and 407,000 trees later, Los Angeles has a new mayor, and the MTLA program continues to plant and steward trees with its partner organi- zations (Los Angeles Times Editorial Board 2013). In 2006, the USDA Forest Service undertook a study to estimate future benefits from planting one million trees (McPherson et al. 2008b). This study replicates that assessment, but uses tree planting and survival data for the early years instead of prelimi- nary estimates. Findings from the two studies are then compared to evaluate how MTLA trees are per- forming relative to the preliminary estimates. Tree survival and growth rates are compared to results from other programs and subtropical urban for- ©2014 International Society of Arboriculture ests. This study serves as a benchmark for gauging MTLA’s future success and comparing with results from other large-scale tree planting initiatives (TPIs). The MTLA Program MTLA is one of several mayoral TPIs launched in the largest U.S. cities that have together pledged to plant nearly 20 million trees (Young 2011). The complexities associated with implementing the MTLA program are daunting (Pincetl 2010). MTLA does not take money from the city’s gen- eral fund. It is administered by the Department of Public Works and led by employees of the Million Trees LA Foundation, a non-profit organization. It has had a number of corporate sponsors, with many donations of in-kind services and materi- als. Resources are leveraged by MTLA from vari- ous city departments, as well as funding for tree planting from the Los Angeles Department of Water & Power (LADWP) and the South Coast Air Quality Management District. In 2009, the
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