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STATUS OF THE URBAN FOREST (PUBLIC AND PRIVATE TREES) stormwater capture, improved air quality, and aesthetic, financial, and social benefits. To improve the resilience of the urban forest, a city's tree inventory should contain no more than 10% of any one species, 20% of any one genus, or 30% of any one family (Miller and Miller 1991; Richards 1993; Ball 2007). These recommendations provide useful guidelines to measure the vulnerability of the City's tree population. Pleasanton's 23,722 City -managed trees are composed of 113 genera and 250 species. The top 10 genera and species are shown in Tables 2-7 and 2-8. Sustainability goals are as follows: ■ Sustainability Goal (Genus): No genus represents more than 20% of inventory. ■ Sustainability Goal (Species): No species represents more than 10% of inventory. An exception to the genus and species goals above are for native species such as oaks, which may exceed the recommended sustainability goals. The City and community have put a high value on native species as these trees are naturally adapted to Pleasanton's local environment and climate, and provide habitat to a wide variety of native animals. The oak genus Quercus currently makes up just over 20% of the inventory and the two most common oak species (coast live oak and valley oak) within the City make up 9.4% and 7.2%, respectively, of the overall species in the inventory. Another exception to consider for the City are tree species that already have a proven history of resiliency in Pleasanton's urban landscape, which might include species that have already survived extreme heat and drought periods, recovered from pest infestations, or that have successfully grown in limited spaces with suboptimal soil volume. 130 1 CITY OF PLEASANTON URBAN FOREST MASTER PLAN