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