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CITY OF PLEASANTON URBAN FOREST MASTER PLAN | 17 <br /> KEY FINDINGS <br />will need to maintain health during periods of drought and <br />extreme heat. Trees that are in poor health and stressed <br />are more susceptible to invasive pests and diseases. The <br />species composition and diversity of trees in Pleasanton’s <br />urban forest play a central role in long-term urban forest <br />health. Beginning to plant tree species that are likely to <br />be adapted to future climate conditions and diversifying <br />the overall makeup of the City inventory will create a <br />more resilient urban forest against these threats. A good <br />example of a recent issue that may become a bigger threat <br />in the future is Dutch elm disease. In 2020, a number of <br />American elm trees in Civic Park were affected by Dutch <br />elm disease (see photo to right), which is a fungus carried <br />by two species of bark beetles that initially causes dieback <br />in the leaves and branches and may eventually lead to the <br />death of the elm tree. By diversifying the City’s downtown <br />trees, we can better ensure that the canopy endures even <br />if one or more species are threatened. <br />Page 248 of 348