Million trees LA canopy cover assessment

The Million Trees LA initiative intends to chart a course for sustainable growth through planting and stewardship of trees. The purpose of this study was to measure Los Angeles's existing tree canopy cover (TCC), determine if space exists for 1 million trees, and estimate future benefits from the planting. High-resolution QuickBird remote sensing data, aerial photographs, and geographic information systems were used to classify land cover types, measure TCC, and identify potential tree planting sites. Benefits were forecast for planting of 1 million trees be-tween 2006 and 2010, and their growth and mortality were tracked until 2040. Two scenarios reflected low (17 percent) and high (56 percent) mortality rates. Numerical models were used with geographic data and tree size information for coastal and inland climate zones to calculate annual benefits and their monetary value.

Los Angeles's existing TCC was 21 percent, and varied from 7 to 37 percent by council district. There is potential to add 2.5 million additional trees to the existing population of approximately 10.8 million, but 1.3 million of the empty tree sites are deemed realistic to plant. Thus, there is space for planting 1 million new trees. Benefits for the 1 million tree planting for the 35-year period were $1.64 billion and $1.95 billion for the high- and low-mortality scenarios, respectively. Average annual benefits were $49 and $60 per tree planted. Eighty-one percent of total benefits were aesthetic/other, 8 percent were stormwater runoff reduction, 6 percent energy savings, 4 percent air quality improvement, and less than 1 percent atmospheric carbon reduction. Recommendations included developing a decision-support tool for tree selection and tracking, as well as establishing a model parking lot greening program.