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Davey Resource Group, Inc. <br />Tree Inventory Analysis & Maintenance Strategy <br />Page 4 <br />Section 1: Structure And <br />Composition <br />The City of Orono contracted arborists who collected data on tree sites along the street ROW and in public <br />parks throughout Orono; 4,602 sites were inventoried, with 63% collected along the street ROW and 37% <br />collected in parks (Figure 1). <br />SPECIES & GENERA DIVERSITY <br />Diversity within plant communities is important for <br />increasing their resistance and resilience to disturbance <br />(see side panel, “The Importance of Species Diversity”). <br />The 10-20-30 rule is a common urban forestry industry <br />metric for tree species diversity in which a single species <br />should compose no more than 10% of the population, a <br />single genus no more than 20%, and a single family no <br />more than 30%. Some communities may be in the <br />position to pursue more aggressive diversity goals, such <br />as a 5-10-15 metric. <br />There are 80 different species within Orono’s ROW <br />and parks; however, there are five species collected <br />that do not typically grow in this region. These species <br />include Cornelian cherry (Cornus mas), Lodgepole pine <br />(Pinus contorta), loblolly pine (Pinus taeda), Cascara <br />buckthorn (Rhamnus purshiana), and western red cedar <br />(Thuja plicata). Figure 2 shows the species diversity <br />breakdown for Orono’s most common inventoried trees. <br />Green ash is the most common tree (26%), followed by <br />boxelder (9%) and sugar maple (8%). <br />The City’s inventoried trees represent 32 distinct genera. Figure 3 shows the genera diversity breakdown <br />for Orono’s inventoried trees. Ash is the most common genus (27%), followed by maple (22%), elm (11%), <br />and spruce (7%). <br />THE ROLE OF NON-NATIVE TREE SPECIES <br />IN THE URBAN ENVIRONMENT <br />Certain non-native tree species that are especially tolerant of harsh urban <br />conditions can be a practical choice to plant, especially when aiming to sustain <br />high levels of species diversity. Non-native species of concern are those that are <br />considered invasive, which should not be planted regardless of the site <br />conditions. <br />2,903 <br />1,699 <br />0 <br />500 <br />1,000 <br />1,500 <br />2,000 <br />2,500 <br />3,000 <br />3,500 <br />TreesNumber of SitesStreets Parks <br />Figure 1. Number of inventoried sites by location and type. <br />16