288 vival rates over a 35-year period (2006–2040). A low-mortality scenario assumed annual loss rates of 1% for establishment (the first five years aſter planting) and 0.5% for the remaining 30 years. The high-mortality scenario assumed annual loss rates of 5% during establishment and 2% thereaſter. Overall survival rates for 35 years were 82.9% and 44.5% for the low- and high-mortality scenarios. Over 35 years the value of benefits from planting one million trees was estimated to total $2.0 to $1.3 billion for the low- and high-mortality scenarios. These values translated into $1,951 and $1,328 per tree planted, or $56 and $38 per tree planted per year. The average annual benefit per tree planted was $4.37 and $2.78 for rainfall interception (low and high mortality), $3.35 and $2.16 for energy sav- ings and $2.38 and $1.32 for air pollutant reduction. Were these projected benefits overly optimistic or are they becoming a reality? Eight years is not sufficient time to conclusively answer this ques- tion. However, it is possible to identify trends that will influence future benefits. To assess these trends, this study examines the types of trees planted, their survival, and growth. Are they pri- marily large-stature trees capable of producing substantial benefits or smaller-stature trees, as assumed in the preliminary study? How do their survival and growth rates compare with those reported for other programs? This study is novel in its use of a TPI’s planting, growth, and survival data to identify trends that will influence future program benefits. The goals of this second study of the MTLA program are to: 1) evaluate the sur- vival and growth of MTLA plantings during its early years because of their potential impact on future tree benefits, and 2) compare estimates of future benefits based on these data with those previously reported using preliminary METHODS Study Area The study area covers 1,022 km2 of urban land in Los Angeles, California (latitude: 34°06’36”N, lon- gitude: 118°24’40”W). The climate of Los Ange- les is Mediterranean, characterized by hot, dry summers and cool, rainy winters from October through April. Average annual rainfall is 345 mm and the average annual and lowest temperatures ©2014 International Society of Arboriculture data. McPherson: Monitoring Million Trees LA recorded are 19°C and -4°C, respectively. Los An- geles has a variety of climate zones because of its proximity to the Pacific Ocean and nearby moun- tain ranges. Portions of Los Angeles fall into two of the sixteen U.S. climate zones that were used in the preliminary MTLA study for benefit calculation (McPherson et al. 2011). The two climate zones are hereaſter referred to as Coastal and Inland zones. Computer Simulations This study uses computer simulation methods described in the initial MTLA assessment with a few exceptions (McPherson et al. 2008b). The simulation period is 40 years, instead of 35 years. Planting rates are based on reported numbers of trees planted, instead of a priori estimates. The simulation assumes that trees were planted in the spring for the first five years (2006 to 2010). Instead of using low- and high-mortality rate sce- narios to simulate future benefits, this study uses a single scenario. Establishment period survival rates (first five years) are based on field sampled data. A single literature-based mortality rate is assumed for the remaining 35 years. This simu- lation and the previous analysis assumed that dead trees were not replaced. Results here are reported for trees planted in street, park, and yard locations to reflect observed differences in species composition, growth, and survival. The accuracy of computer simulation estimates depends on the quality of underlying simplify- ing assumptions, as well as the numerical models. Assumptions known to influence results in sub- stantial ways are described throughout this paper. However, a comprehensive sensitivity analysis has not been conducted, so the precision of each esti- mate can only be described in qualitative terms. To determine if the values reported here are reason- able, the values are compared to previously pub- lished estimates for trees in similar climate zones. Additional research is needed to determine the importance of simplifying assumptions, establish confidence bounds, and direct future research. Tree Planting Survey Information on the numbers and species of trees planted in street, park, and yard locations was ob- tained from 2006 to 2010. Street and yard data came from databases maintained by MTLA (pers. comm.,
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