Arboriculture & Urban Forestry 40(5): September 2014 establishment. Three percent annual mortality rate was used for modeling thereaſter, based on a recent meta-analysis of 16 street tree survival studies that found annual mortality rates typically ranged from 3% to 5% (Roman and Scatena 2011). The previous study assumed lower post-establishment loss rates, 1% and 2% for the low- and high-mortality scenarios. The random field survey of 70 yard trees found 54 alive and 16 missing. Survivorship was 77.1% and the average annual mortality rate was 4.6%. For modeling purposes, this rate was applied for the first five years, aſter which a 3% annual mortality rate was assumed. TreePeople conducted a three- year survey of 225 park trees planted in 2008 and found that 204 were alive in 2011 (90.7% survivor- ship) (pers. comm., Ryan Allen, Tree Care Man- ager, TreePeople, Los Angeles, CA; July 7, 2011). Based on these data, park tree average annual mor- tality rates were modeled as 5%, 4%, and 2% for years 1, 2, and 3 through 5 aſter planting, respec- tively. A constant rate of 1.5% was assumed for the remainder of the 40-year planning horizon. The modeled street tree population reached 50,038 in 2010, then gradually dropped to 17,231 in 2045, or 31% of the number planted (Figure 1). The modeled park tree population had the high- est survival rate, peaking at 11,349 and finishing at 6,687, or 54% of the 12,472 planted. Modeled yard trees exhibited the lowest survival, their popula- tion reaching 20,023 and closing at 6,895 (30%). Across all locations, 33.6% or 30,813 trees of the 91,786 planted were projected to survive until 2045. Aſter 40 years, the simulated total basal area for street, park, and yard trees was 31,030 m2 m2 , 12,677 , and 10,896 m2 (Figure 1). Although over 10,000 more yard trees were planted than park trees, the total basal area of simulated park trees exceeded yard trees aſter the year 2032. Parks were planted with relatively more large-stature trees that had higher survival rates than simulated yard trees. Street 1,269 2,532 2,727 1,311 8,333 2006 2007 2008 2009 2010 coastal 494 Street inland 3,869 8,230 13,301 16,172 6,549 48,121 Park 263 159 191 215 1,372 Park CO2 Stored and Avoided Emissions year period was 73,703 metric tonnes (t), valued at $1 million, assuming a price of $14 per t (Table 5). Simulated street and park trees accounted for 55% and 28% of the total amount, respectively. Across all locations, the projected amount of CO2 The estimated amount of CO2 stored 40-year period varied among species (Figure 2). For example, 187 Quercus agrifolia planted in the Coastal streets location were projected to store 221 t CO2 per tree planted per year was 20.1 kg. Values ranged from 9.7 kg (Coastal, yard) to 44.2 kg (Inland, park). Projected amounts of CO2 stored over ing and climate effects of trees on building energy use were estimated to total 101,679 t over 40 years ($1.4 million) (Table 5). Ninety-seven per- cent of this amount accrued Inland, where most trees were planted (69,173 versus 10,142 trees) and air conditioning loads are greater than in the Coastal climate zone. Across all locations, the pro- jected amount of CO2 Q. agrifolia (3.0 t), Pinus canariensis (3.3 t), and Fraxinus uhdei (5.4 t). Lagerstroemia indica (0.1 t) and Pistacia chinensis (0.4 t) stored the least. Avoided CO2 523 Pyrus calleryana. Species that stored the most CO2 emissions avoided per tree planted per year was 27.7 kg. Values ranged from 7.7 kg (Coastal, yard) to 36.2 kg (Inland, street). The effect of tree shade and air temperature increase heating loads and associated natural gas consumption by 12,557 gigajoules (GJ) and 9,208 GJ for street and yard trees, respectively. Equiva- lent CO2 emissions totaled 1,101 t for 40 years. Table 2. Distribution of planted trees by year, location (street, park, yard), and climate zone (Coastal, Inland). Year Yard coastal 543 inland 4,392 2,132 1,290 1,548 1,739 11,100 coastal 426 456 222 360 345 1,809 Yard inland 3,833 4,817 2,711 3,610 6,081 21,052 Grand total 13,557 17,166 20,215 24,608 16,240 91,786 reductions on cooling loads was estimated to be 116,909 MWh and 46,598 MWh in street and yard locations over the 40-year period (Table 6). These cooling savings translated into 102,779 t of avoided CO2 emissions. Trees were estimated to the , or over twice the amount (92 t) stored by per tree planted were Platanus racemosa and emissions attributed to shad- stored over the 40- 293 ©2014 International Society of Arboriculture
September 2014
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