Nearly 40 percent of Durham’s 108 square miles are covered by trees. However, without proper maintenance of the existing inventory and systematic replanting efforts, this percent is at risk of decreasing. The city must plant an estimated 1,680 new trees every year for the next 20 years in order to maintain the current canopy coverage.
For many Durham residents, the fragile state of thousands of willow and water oaks planted in the 1930s is all too familiar. Not only are the willow and oak populations near the end of their natural lifespans, construction, vehicle exhaust, improper pruning, and cankerworms have have also weakened the trees’ health. By some estimates, Durham will lose an average of 650 of these large trees and 100 smaller trees per year over the next 20 years due to storm damage, accident and natural attrition. Currently, the city removes 750 or more dead and dying trees annually, a number that can rise due to natural disaster, disease, and pests.
The City of Durham hired Raleigh-based Leaf & Limb to inventory the aging willow and water oak populations in the city rights-of-way in order to create a digital map of the trees. Katie Rose Levin, an arborist consultant with Leaf & Limb and manager of the project with the City of Durham, has extensive experience helping clients collect and leverage tree inventory data for prioritizing maintenance, long-term planning, and regulatory compliance.
While inventories can be expensive and time-consuming to complete, they are essential for allowing organizations to plan for losses and gains and performing a cost-benefit analysis on maintenance activities. “You cannot manage something if you don’t know what you’re managing,” said Levin. With consistent tracking of data, a tree inventory becomes a living document that you can use to develop a master plan, make data-driven management decisions and track maintenance work. “Every city should have an inventory of all its infrastructure. Just as other infrastructure records need to be updated by technicians following maintenance, trees must be mapped and tracked, too,” said Levin.
Leaf & Limb worked closely with the City of Durham to define a list of data collection fields and develop a set of guidelines for assessing the trees. “It’s important to understand how the data collected is being used. The goals of the tree inventory will dictate what information is being collected,” said Levin. Levin trained staff to recognize insects and diseases specific to willow and water oaks before going out in the field to collect data. Collecting extraneous data increases inventory costs and total time required.
According to Levin, it often makes sense for a contractor to complete an inventory for a city. Inventories are time intensive and require a specialized set of knowledge and tech savvy, which can make it difficult for municipalities to complete while also staying on top of their routine activities. Leaf & Limb chose to collect the data using OpenTreeMap as it was customizable, mobile-friendly and could be easily added to Durham’s existing tree map. Alex Johnson, the City of Durham’s Urban Forestry Manager, also noted that he did not want the data collected in a proprietary platform that would make it difficult to use later. He wanted a platform that did not require technical expertise and could use used to engage the community in stewardship activities.
The city also plans on completing a canopy analysis to establish a baseline, and set a goal of what percentage canopy coverage they want to maintain across the city. It is important that the city continues to calculate canopy coverage on the neighborhood-level. Studies have highlighted the lack of tree planting in poorer neighborhood. In recent years unequal distribution of canopy in cities can be exacerbated by the fact that cities tend to plant trees where trees have been recently removed. Canopy coverage data can help the city more effectively close the gap.
You can find more information on how technology can support the long-term monitoring of urban trees; assist with tree planting and maintenance data processes, and enable data to be organized and shared in a report prepared by Azavea for the Pennsylvania Horticultural Society and the USDA Forest Service Philadelphia Field Station.