Application Feature by Trimble
Although the many benefits of trees are well-documented, urban forests continue to steadily decrease in significant numbers. The U.S. alone loses four million urban trees per year.
Over the past decade, a number of ambitious million-tree initiatives have been launched to try to stem the urban loss of green. However, at the root of these planting campaigns is the million-dollar question: How can cities achieve the goal? And the equally important, second question: Is this goal even achievable with the existing urban space?
Since 2006, Jarlath ONeil-Dunne, director of the University of Vermonts (UVM) Spatial Analysis Lab, and a team of US Forest Service scientists, have been helping city officials answer those how much questions by integrating spatial data such as satellite imagery, LiDAR, aerial photos, and GIS datasets into Trimbles eCognition image-analysis software to produce urban tree canopy (UTC) assessments. The UTC information indicates how much tree canopy exists, where the trees are and what space is left in which to plant. The resulting data enables planners to set realistic goals for increasing their green infrastructure and develop targeted campaigns to maintain the canopy they have.
Tree Report Cards
Although the outcomes of the UTC studies depend on the available source data, typically the UVM analysts are given a combination of geospatial imagery such as high-resolution aerial photos, satellite images, LiDAR data, and GIS datasets such as roads and buildings. Using eCognition, they incorporate the imagery into the software and create customized rule sets, workflows of if-then scenarios to automatically classify and map specific vegetative types and environs.
Typically each client receives a report detailing their tree canopy percentage, a complete land-cover map, and the customized UTC GIS datasets, enabling users to examine and view the tree cover down to the individual property parcelor the entire city.
This type of perspective is providing cities such as Baltimore, Pittsburgh, New York City, and Washington, D.C., with the definitive means to prioritize strategies to meet their tree-canopy goals.
Stemming the Storm Water in Baltimore
Based on a 2008 UTC assessment, Baltimore has an urban tree canopy of 27 percent, with a goal of reaching 40 percent by 2037. The citys impervious surfacesstreets, buildings, parking lotscomprise 43 percent, however, and that imbalance is problematic, particularly for managing storm water runoff.
With the aid of the UTC data, city leaders have initiated tree-planting campaigns to address surface runoff as well as other urban renewal improvements. Since 2009, foresters and volunteers have planted 27,000 trees.
Simply put, you manage what you measure, says Morgan Grove, a research scientist based in Baltimore with the USDA Forest Service. The UTC data is a complete census of the landscape that you can integrate with other city data layers to answer specific questions and prioritize efforts.
Urban Renewal in Pittsburgh
With an estimated UTC of 42 percent, Pittsburgh seems to have a rather commendable green landscape. However, that 42 percent is misleading, says Danielle Crumrine, director of Tree Pittsburgh, a local advocacy organization.
Large swaths of our trees are on steep hillsides, which is not where our residents live, she says. So theyre not shading our homes or pulling storm water off the streets. Thats an issue of imbalance that the UTC data, as part of our urban forest master plan, is helping us to resolve.
Incorporating the UTC analysis with other tree-related data, Tree Pittsburgh created an urban forest master plan in 2011 to serve as a roadmap to help grow the citys tree canopy by 20 percent in 20 years. With such a tool, Crumrine and her team have transformed their former plant-by-request model into a pre-planned, targeted approach to address tree inequities and energize residents and businesses to help blanket the city in green.
One example is a pilot project launched in 2012 to address underserved communities. They used the UTC dataset to identify the 25 lowest-canopy neighborhoods; teams then inventoried 23 parks, pruned 35 trees, removed three trees and planted 80 trees. The project will continue and Crumrine plans to use the same approach in other areas.
A Million Trees in NYC
Sprouting a new tree-planting prioritization model has also been one of the significant benefits of the UTC analysis for the New York City Department of Parks and Recreation (NYC Parks) in its endeavor to meet the citys MillionTreesNYC initiative.
With MillionTreesNYC, we receive so much funding for planting that responding to just tree-planting requests would never help us reach our goal, says Jacqueline Lu, director of GIS and analytics with NYC Parks. The UTC data enabled us to change from a request-based program to a block-planting model, where we use geospatial data to identify areas with a high need for trees and plant it out completely. Its much more effective.
Indeed, 820,330 trees have been planted across New Yorks five boroughs since the MillionTreesNYC initiative began, nearly guaranteeing the city will reach its revised one-million-trees goal by 2015two years earlier than the original 2017 timeline.
Returning Washington, D.C., to the City of Trees
Decisions rooted in trees is what the advocates at Casey Trees (CT), a local non-profit organization, is striving to achieve through its own canopy goal of 40 percent. From Washington D.C.s peak of 50 percent in 1950, the former City of Trees has lost 2.5 percent of its tree canopy every decade. Based on the UVMs 2011 UTC assessment, Washingtons tree coverage is 36 percent; its impervious surface coverage is 41 percent.
The fact that we now have more impervious surface than we do tree canopy is greatly concerning, says Mark Buscaino, CTs executive director. And recently, much of the tree loss stems from rapid urban development. The striking images of the tree canopy data are a tremendous communication and education tool to help us achieve a balance between development and green space.
The amount of hard surface in DC has posed enough of a storm water management issue that the federal Environmental Protection Agency (EPA) imposed regulations requiring it to adopt measures to reduce rainfall runoff. In 2008, the mayor launched a tree-canopy goal of 40 percent by 2035; in 2013 that was revised to 40 percent by 2032.
To achieve that, existing trees need to be preserved and 216,300 new trees must be planted. Aided by the UTC analysis data, teams have planted more than 30,000 trees since 2008 and devised maintenance strategies to protect its existing green landscape.
Indeed, with detailed, accurate datasets such as UTC assessments, planners and foresters can get to the root of their canopy problem, devise efficient, tactical greening strategies to better the canopy, and possibly nip future issues in the bud. After all, the best time to plant a tree was yesterday.
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