Composition and dominance in Los Angeles Basin urban vegetation

A survey of Los Angeles area urban vegetation was done in 1982 as an integral part of a larger project to determine an emmissions inventory for reactive organic compounds such as isoprene and monoterpenes. A random, multistage sampling procedure was used. The Los Angeles coastal plain was subdivided into 20 polygons based on distinctive reflective characteristics on color-infrared images obtained from a 1972 U-2 overflight. Ground sampling in randomly selected sub-areas of each polygon identified a total of 184 plant species distributed in six structural classes: broadleaf trees, conifers, palms, shrubs, grasses, and ground covers. The leafy crown volume and the area of ground surface occupied was determined for the most frequently encountered species, and the dry leafmass constant (gm^-3) was determined for 51 common species. A similarity index was used to compare the species composition of ground-sampled areas. All areas classed as residential had a mean index of 0.57 ± 0.07. Nonresidential compared with residential areas gave a mean index of 0.41 ± 0.16. Species with the highest importance values were California fan palm, Italian cypress, Monterey pine, Cocos palm and Canary Island pine. These data have implications for several aspects of landscape planning including the proper selection of species to provide maximum shading, air filtering capacity, noise suppression and a capacity for surviving polluted air and limited root space.