California’s native trees and their use in the urban forest

Abstract

California’s urban forest is composed of both native and non-native species. These trees improve the quality of life of urban residents and mitigate the effects of climate change by buffering local microclimates. A species’ native status is often defined at the scale of the state’s political boundaries, which doesn’t reflect its actual native range. Here we define the list of 95 tree species native to California, create digital range maps for each species, provide native species lists for every city in California, and analyze trends in native tree species in the state’s urban areas. We found that California’s urban areas have relatively few tree species that are native within a given city’s boundaries. Even though non-natives outnumber natives in all California cities, opportunities for more native tree diversity are slim as most cities have less than four native species that aren’t already growing as urban trees. California’s cities face a hotter and drier future, threatening existing urban forests and the benefits they provide residents. We explore different options for tree selection based on the goal of growing healthy and resilient urban forests into the future.