UFA was looking to expand its management reach from its portfolio of street tree maintenance and tree permitting to oversight on trees in other public spaces. Schools and parks had previously been responsible for maintaining trees on their own properties, and as a result, the city never had an integrated or managed focus for all municipal trees. Agency officials knew they could handle managing the additional trees, but the proposal was difficult to prove when they could not answer a simple question: How many new trees would UFA be responsible for maintaining?
The foresters began to look at ways to estimate or assess the number of trees and found the perfect answer with lidar, which uses timed pulses from an airplane-mounted sensor to create high-resolution maps. Fortunately for UFA, the U.S. Geological Survey had recently conducted a large-scale lidar flight of the Eastern Seaboard to evaluate damage from Hurricane Sandy, which generated the necessary data for the assessment. With the help of filtering and processing algorithms, officials used the data to produce an accurate citywide map detailing individual trees by their heights and crown widths.
The lidar map answered the original question, but the more the foresters used the data, the more opportunity they discovered. “We knew it would give us answers in certain limited applications, but it could also answer questions we weren’t even asking,” said Earl Eutsler, UFA’s deputy associate director.
For example, field arborists at the time faced difficult enforcement challenges in their effort to ensure that construction companies and residents secured the necessary removal permits required for “mature” trees, or those of a certain size. Arborists could not determine which removals violated the law even when they discovered the results. But with lidar data, UFA staff could quickly find a removed tree’s original height and determine whether the removal was illegal, allowing the agency to more effectively enforce permitting laws.
“The word has gotten out about the applicability of these laws and the city’s ability to administer them after the fact,” Eutsler noted, pointing to a recent increase in permits after UFA successfully used lidar to fine a developer. “It bolsters the case that it’s easier to apply for a permit than it is to try to skirt around the law.”
“As excited as arborists seem about enforcement, they get even more excited about their ability to showcase where we’re making the greatest gains,” said Eutsler. For example, comparing current and previous data allows the agency to easily locate and highlight successes in its tree-planting programs. All UFA data is also publicly available on D.C.’s open data website, which has increased civic engagement and raised interest from universities, research institutions and nonprofits.
Looking forward, D.C. plans to continue integrating lidar into new areas. Besides fine-tuning its models to lower error margins, the city is building a modeling tool that combines lidar and elevation data to find the best place to plant trees in order to mitigate the largest volume of stormwater. This would allow arborists to plant more strategically and maximize the impact of their work.
Washington, D.C.’s use of lidar shows how applying new technologies to government problems can reveal even more possibilities for tech-driven innovation. What started as a simple query to use data to count trees has transformed UFA into a smarter, more innovative and more efficient agency. It’s a prime example of how a city can take full advantage of all that its data can offer.
