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Making the Most of Urban Trees

Ah! The sound of the forest….the urban forest, that is."This is a lace bark elm…”On this steamy afternoon, grad student Alvin Rentsch is methodically traveling the sidewalks of downtown Louisville with a clipboard and a hand-held GPS. He’s been trained to identify tree species, and mark each tree’s location, health, and size.“It’s a 20 feet in canopy, does it have enough canopy space, is there any impediment from the building, what is the growing space, and we’ll call that a well and give it 8 feet.”Rentsch’s and others data will go into a new database the city is creating with this inventory of downtown trees. The main idea is to paint the bigger picture: what trees are performing well and where. With that baseline, city landscapers can establish a regular maintenance schedule for each tree, depending on its species and age and condition. They can make better decisions about which trees to plant where. Public works spokeswoman Betty Yoonis says inventorying trees now should improve the way the city manages its trees over the long term.“Certainly there’s a system to it, but it’s more, you know, we get a call from a concerned citizen, or one of our staff sees a tree that might have an issue. We were dealing with it that way. This program and the management plan which is resulting from it allows us to be proactive instead of reactive.”University of Louisville mapping expert Bob Forbes says the data will also help the city calculate the extent to which trees are cleaning up the atmosphere… and even help city arborist Mark White maximize those efforts.“There are computer programs that allow us to calculate how much oxygen are we actually creating from all these trees, what pollutants and how much are we actually filtering out of there, so that when Mark decides what kind of trees to plant, he can look at the database, he can look at those trees that are the most efficient, and use that as a guide to future plantings.”For now the city’s tree inventory is limited to the central business district, downtown. But what might the inventory look like in the neighborhoods? Rich neighborhoods, poor neighborhoods? University of Louisville grad student Shannon Scroggins is part of research team trying to answer those questions.In the muggy side yard of a St. Matthews brick home, Scroggins takes some tree measurements. She flips through a tree brick to identify the species—an eastern red cedar, with lacy needles and blueberry-colored cones. This is on of several plots she’ll hit this summer. Scroggins says it’s one of 10 metro council districts chosen for the study, each with a different racial make-up, income levels, education levels, and age of the housing stock. “And then we’re going to use those socio-demographic variables to see if there’s any patterns across these council districts with what we’re finding with tree cover, etc.”U of L professor Margaret Carreiro leads the study. She’s interested, for example, in whether or not rental properties have more or less tree cover than homeowner properties, and how trees have been managed or mismanaged in poor neighborhoods. Carreiro’s research will go beyond the city’s inventory in that she’s looking at the direct relationship between a tree and its nearby building.“Based on direction and the size of the tree, the size of the building, they can tell the extent to which, in your latitude, that tree is cooling you, cooling that building, in the summer.”She will even be able to translate that into a dollar value.“You put things into dollar signs, then planners and policymakers can compare those values with other land use options – development in one sector vs. another—or for developing ordinances to protect our trees.”With two major tree surveys underway in the city, planners should soon have a wealth of information about how to manage our urban forest for decades to come. It’s a sign that cities are beginning to recognize that trees do more than fill public spaces.