UCLA

Interest in urban vegetation has increased dramatically. Urban trees are an important aspect of the urban environment but there is little known about the potential sources of those trees, change in tree species diversity over time and the factors leading to the contemporary floristic composition in cities. We investigate tree nursery offerings in Los Angeles County over the past 110 years through the use of here-to-fore unexplored nursery catalogs to determine the diversity of trees that have been commercially available over time. Tree species information was collected spanning a 110-year study period and analyzed the data for four time periods (1900-1929, 1930-1959, 1960-1989, and 1990-2011). We found the number of genera and tree species offered significantly increased in the past 20 years (1990-2011). The numbers of non-native trees, angiosperms, and deciduous species all significantly increased with but no changes were observed in the numbers of native, evergreen, or gymnosperm species offered over this time period. The largest numbers of palm species were offered in 1900-1929. Overall there were 562 unique species offered belonging to 201 different genera in the 120-year study period, 48 species were California native trees and 514 of these were non-native species indicating that perhaps Los Angeles has one of the most diverse number of tree species offered for sale by the nursery industry. © 2013 Elsevier B.V.