Success Story: Tree Canopy Assessment
Wake County completes a tree canopy assessment
Project Purpose
Wake County has experienced rapid population and job growth over the last decade. This growth has driven development in the county, a trend that is expected to continue. Rapid land use change, like changes in tree canopy, can have implications for climate resilience. Tree canopy helps protect communities from climate hazards like extreme heat and poor air quality. Wake County recognized that measuring tree canopy would help protect this source of community resilience, so staff decided to conduct a tree canopy assessment.
Quick Facts
- The population of Wake County has increased by almost 25% from 2010 to 2020. This makes it one of the fastest growing counties in North Carolina (Wake County Government, 2023).
- The tree canopy assessment was part of a larger land cover analysis project that covered all 857 square miles of the county.
- All 12 Wake County municipalities participated in the tree canopy assessment. At the conclusion of the project, each municipality received a copy of the report.
- The tree canopy assessment helped Wake County consider land cover issues across the county’s highly variable landscape. The County will use the assessment to make decisions about urban, suburban and rural planting initiatives.
Understanding tree canopy assessments
A tree canopy assessment provides a map and a measure of a community’s tree canopy cover. Communities use this information to set tree canopy goals, make decisions on where to increase tree planting efforts and more. Assessments are conducted using remote sensing imagery such as LiDAR data or high-resolution digital satellite aerial photographs. These images are stitched together to create a community-wide map and then digitally analyzed to measure the proportion of tree cover.
Tree canopy assessments are different than tree inventories, which are on-the-ground data collection efforts that provide information on tree species diversity, tree size and tree condition. However, some LiDAR tools can provide information on tree species and size.
Resilience benefits of trees
Studies have found that a good tree canopy can provide aesthetic benefits, influence property values and increase stormwater infiltration. Trees also help reduce summer peak temperatures and reduce air pollution (EPA, 2023; EPA, 2023; Kovacs, West, Nowak, & Haight, 2022; National Park Service, 2022)
Spotlight on Equity
One aim of the canopy assessment was to achieve a higher quality of life for residents in low-income areas and areas vulnerable to climate hazards. Wealthy areas, on average, have more tree canopy cover than low-income areas (Gerrish & Watkins, 2019). Low-income areas are also more vulnerable to the negative effects of urban heat islands. Urban tree canopies are excellent sources of shade and help to cool their surroundings. Communities can use the data from a tree canopy assessment to prioritize planting initiatives in the most vulnerable areas.
| Key Info | |
|---|---|
| Location | Wake County, N.C. |
| Estimated Costs | $350,000 |
| Published | March 1, 2024 |
| Project Contact |
|---|
| Liz Oliver Project Administrator Wake County liz.oliver@wake.gov (919) 856-6329 |
| Related Resources |
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- Wake County sent out a call for proposals for a land cover analysis in July 2021. In September 2021, the County selected a vender.
- In November 2021, the County organized a committee to oversee the analysis’ completion.
- The tree canopy assessment portion of the project started in July 2022. The contractor delivered the final data in August 2023. The contractor used a combination of remote sensing and ground truthing to map tree cover across the county. Wake County leaned on federally available datasets, when possible, to reduce costs for new remotely sensed data.
- Wake County published the 108-page Land Cover Analysis and Tree Canopy Assessment report online alongside an interactive story map detailing the main findings of the assessment. The report and story map include the history of tree canopy changes in Wake County and the potential for future improvements.
- Following the report, Wake County worked with municipalities and stakeholders to evaluate the findings of the report and identify opportunities to improve the tree canopy. County officials planned pilot planting projects for 2024 based on the assessment results.
- Wake County plans to examine the success of the planting projects around 2027.
- North Carolina allotted $217 million in State and Local Fiscal Recovery Funds to Wake County as part of the American Rescue Plan Act (ARPA). The County used $350,000 of the ARPA funding to cover:
- The core assessment and deliverables ($312,000)
- The mapping software platform ($24,000)
- Tree planting projects ($14,000)
Wake County; municipal stakeholder groups from Raleigh, Cary and Morrisville
- The Wake County Tree Canopy Assessment created a baseline map of the current tree canopy to help the County understand where communities were seeing the benefits of urban tree canopy cover. Wake County will use the map to measure future changes in tree canopy cover.
- The assessment included analyses across a range of geographies like watersheds and planning jurisdictions.
- The assessment report outlined ways a robust tree canopy can help communities manage urban heat islands and improve environmental equity, flooding and stormwater runoff issues.
- The assessment showed that:
- Tree canopy covers roughly 54% of Wake County.
- The total ecosystem services value of the county’s trees is estimated to be just over $3.2 billion.
- Wake County lost 11,122 acres of tree canopy between 2010 and 2020. However, the study identified over 400,000 potential planting locations, totaling around 80,000 acres.
- The assessment is a resource that can guide future tree canopy initiatives, with a focus on equity for vulnerable communities. Municipalities like the City of Raleigh are already working on ways to incorporate tree planting into their local resilience goals.
Wake County Project Administrator Liz Oliver mentioned that the source of remotely sensed imagery you use will determine how easily you are able to build on your study’s baseline analysis over the years. She recommends prioritizing a vendor that uses a reproducible procedure and methodology. This will save you time and money in the future.
Oliver also recommends finding a vendor with a local office who is familiar with the area. Ground truthing results is much easier to do in person. On the other hand, some vendors offer greater levels of automation, which reduces costs and time. These savings may make the project less costly and more feasible for smaller communities or smaller budgets.
EPA. (2023, December 21). Soak Up the Rain: Trees Help Reduce Runoff. Retrieved from https://www.epa.gov/soakuptherain/soak-rain-trees-help-reduce-runoff
EPA. (2023, October 31). Using Trees and Vegetation to Reduce Heat Islands. Retrieved from https://www.epa.gov/heatislands/using-trees-and-vegetation-reduce-heat-islands
Gerrish, E., & Watkins, S. L. (2019, February 1). The relationship between urban forests and income: A meta-analysis. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5726445/
Kovacs, K., West, G., Nowak, D. J., & Haight, R. G. (2022). Tree cover and property values in the United States: A national meta-analysis. Ecological Economics, 197(3): 107424. 13 p.
National Park Service. (2022). Air Pollution Removal by Urban Forests. Retrieved from https://www.nps.gov/articles/000/uerla-trees-air-pollution.htm#:~:text=Trees%20can%20improve%20air%20quality,directly%20removing%20pollutants%20from%20the
Wake County Government. (2023, September 5). New Study Highlights Impact and Importance of Wake County's Trees. Retrieved from Wake County, North Carolina: https://www.wake.gov/news/new-study-highlights-impact-and-importance-wake-countys-trees#:~:text=Wake%20County%20had%2054.2%25%20tree,of%20carbon%20from%20the%20atmosphere