City Trees

Considerations for Urban Foresters The urban forest has always been about more than just the trees. As tree managers we have gone from being mostly focused on arboriculture to also pro- moting the quantifiable benefits of trees to the community. Increasingly, the urban forest is being used strategically to maximize the retention of storm- water and protect the health of our watersheds. Along with increased attention to the intersection of urban forests and stormwater and watersheds comes new funding for tree planting. However, in this arena as with any tree planting effort, the needs of the trees—for sufficient space above and below ground, adequate water, protection from weed com- petition, and other maintenance needs—must be considered if the project is to be successful. While many leaders are setting lofty tree-planting goals and encouraging planting trees, please remember that we don't solve much by simply planting trees; the trees have to grow in order to fulfill their purpose. Previous design efforts for stormwater channeled all the water in pipes away from communities to creeks, rivers, and eventually, to lakes or oceans. Now, we design to guide stormwater back into the ground and aim to manage it on-site versus moving it off-site. Trees can assist stormwater holding areas by pulling water out of the soil to increase the soil's water-holding capacity. Urban natural areas are being retained for stormwater runoff purposes, and increasingly, trees are being considered and preserved in development. The key to including trees in stormwater and water- shed success includes retention of existing tree canopy and restoration of future canopy by planting. In both cases, we have to avoid soil compaction so that water can actually infiltrate the soil and provide ground water recharge. We as arborists and urban foresters must get involved early in development projects to do pre- project site assessment, conduct tree inventories and protected tree evaluations, consult on tree species selection, and make sure the trees are given adequate growing space. We have some leverage, since trees are required for many projects to be accepted by plan- ning commissions and agency councils and boards. We must grow the right tree in the right place for the right purpose, and this takes planning from the earliest stage of development projects—starting with the purpose. Readers of City Trees don't need convincing about the importance of healthy watersheds, but for those who do, a simple way to visualize the serious negative effects that lack of trees has on stormwater runoff and watershed health is to observe the Montecito, California mud- slides of 2018 that occurred after wildland fires removed the vegetative soil cover in that area of Santa Barbara County. The unprotected soils slid and along with debris and rocks caused injury and loss of human life, huge loss of property, and ecological damage to five watersheds. A note about terminology. Personally, I don't like the terms "green infrastructure" and "grey infra- structure." It is all infrastructure and should be considered on equal terms for comparisons of cost, sustainability, and effective design. I encourage us to regard trees and discuss them as an integral part of infrastructure, without the "green" qualifier. —Gordon Mann, Consulting Arborist and Proprietor, Mann Made Resources Publication Link: Accounting for Trees in Stormwater Models Published in 2018 by the Center for Watershed Protection, this pub- lication is intended to help the stormwater engineering commu- nity more easily account for trees in runoff and pollutant load calcula- tions so that they can more readily incorporate them into their storm- water management strategies. www.urban-forestry.com 15

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