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Davey Resource Group, Inc. <br />Tree Inventory Analysis & Maintenance Strategy <br />Page 5 <br />SPECIES & GENERA DIVERSITY <br />RECOMMENDATIONS <br />Avoid or limit planting of green ash and increase <br />planting of other species until green ash make up <br />less than 10% of public trees. <br />Avoid or limit planting of ash and maple and <br />increase planting of other genera until ash and <br />maple make up less than 20% of public trees. <br />Remove volunteer trees that have invasive <br />tendencies, such as boxelder, from maintained <br />public areas while small. <br />Increase planting of uncommon species and genera <br />which are well suited to urban environments. <br />Figure 2. Species diversity of trees which make up at least 2% of the inventoried population. <br />The Dutch elm disease epidemic of the 1930s <br />provides a key historical lesson on the <br />importance of diversity. The disease killed <br />millions of American elm trees, leaving behind <br />enormous gaps in the urban canopy of many <br />communities. In the aftermath, ash trees <br />became popular replacements and were <br />heavily planted along city streets. History <br />repeated itself in 2002 with the introduction of <br />the emerald ash borer into US. This invasive <br />beetle continues to devastate ash tree <br />populations across the country. <br />Other invasive pests and diseases, severe <br />weather events, and climate change threaten <br />our urban forests today, so it’s vital that we <br />learn from history and plant a wider variety of <br />tree species and genera to develop a resistant <br />and resilient public tree resource. <br />THE IMPORTANCE OF <br />DIVERSITY <br />26% <br />9%8% <br />6%4%3%3%3%3%3%2%2%2% 2%2%2%2% <br />0% <br />5% <br />10% <br />15% <br />20% <br />25% <br />30%Percent of Inventoried PopulationOrono Industry Recommendation <br />17