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Davey Resource Group, Inc. Tree Inventory Analysis & Maintenance Strategy Page 14 SEQUESTERING AND STORING CARBON Trees are carbon sinks, which means they absorb carbon from the atmosphere– the opposite of carbon sources which produce and emit carbon into the atmosphere. While carbon is released from fossil fuel consuming vehicles and smokestacks, it is absorbed by trees during photosynthesis and stored in their tissue as they grow. Orono’s public street trees sequester (absorb) an estimated 27 tons of carbon each year, valued at $11,854, and have stored 1,964 tons of carbon over their lifetime, valued at $849,963 (Table 3). CONTROLLING STORMWATER Trees play a significant role in local hydrology and water cycling helping to reduce the amount of stormwater runoff generated during rain events (Figure 9). Since stormwater runoff can cause infrastructure damage and flooding, reducing the amount of precipitation that becomes surface runoff can save a community costs in infrastructure repair and flooding mitigation. The inventoried trees in Orono divert 399,990 gals. of stormwater each year valued at $3,574 (Table 4). REPLACEMENT VALUE Replacement value is the approximate cost to replace an existing tree with a tree of a similar size and species. While doing this is typically not possible – for example, to replace a 20-inch diameter tree with another tree of similar size would not be feasible – replacement value can provide an idea of the overall value of the inventoried public trees in the city of Orono. In total, Orono’s inventoried trees have a replacement value of $3.05 million. Table 6 compares the per-tree replacement value of the street and park trees with the overall highest replacement values. Bigtooth aspen is the most valuable tree in Orono among both the park and street tree populations, with black maple and silver maple also making the top five. Park trees generally have a greater per-tree replacement value than street trees, likely due to the greater age and larger size of park trees versus street trees in Orono at the time of inventory. Figure 9. Hydrological functions of trees. Source: ‘Stormwater to Street Trees: Engineering Urban Forests for Stormwater Management’, EPA publication 841 B 13 001. 26