WAKE COUNTY LAND COVER ANALYSIS & TREE CANOPY ASSESSMENT

The purpose of the Wake County Land Cover Analysis and Tree Canopy Assessment (LCA/TCA) is to provide data to guide and support planning and implementation efforts on both a county and municipal level.

This project was made possible by the American Rescue Plan Act (ARPA), which provided $5.7 billion to North Carolina for the state’s direct use.

The full Wake County Land Cover Analysis/Tree Canopy Assessment Report is available here:

A land cover analysis was conducted by Davey Resource Group, Inc., a national urban forestry consulting firm, in collaboration with the Wake County Government. With the help of the vendor the analysis was performed countywide to identify the land cover composition of the 857 square miles comprising Wake County. Utilizing 2010 and 2020 vintage imagery made available by the United States Department of Agriculture’s National Agriculture Imaging Program (NAIP), DRG employed geospatial analysis and remote-sensing methods to identify different types of land cover. The assessment utilized leaf-on, multispectral aerial imagery from the 2020 NAIP imagery. Imagery analysis is cost-effective and attains a high degree of accuracy.

Land cover describes the physical surface types of a given area, as viewed from above.

Land cover analysis allows for discovery and examination of landscape patterns and characteristics. In particular, land cover data leads to a better understanding of the impacts of natural phenomena and human use of the landscape.

Land cover data can be acquired from a variety of techniques including remote sensing, ground surveys and aerial imagery. This study utilized an object-based image analysis and semi-automated feature extraction method to process and analyze high-resolution color infrared (CIR) aerial imagery and remotely sensed data.

This analysis classified the entirety of Wake County’s 548, 388 acres of land area into the following five land cover classifications:

Tree Canopy: 297,242 acres Land area that is covered by tree trunks, branches, and leaves, as seen from above. Vegetation: 127, 926 acres Shrubs, grasses, and other low-lying vegetation that allow rainfall to infiltrate soil. Impervious Surface: 81,702 acres Buildings, roads, sidewalks, and other paved or built areas that do not allow rainfall to infiltrate the soil. Bare Soil: 22,692 acres Exposed soil that lacks vegetation, such as vacant lots, construction sites, agricultural fields, and baseball infields. Open Water: 18,776 acres Lakes, ponds, streams, wetlands, and other water features.

After obtaining countywide land cover data, the results were reported and examined across multiple geographic areas of interest, including within unincorporated county, census tracts and block groups, green spaces, watersheds and the planning jurisdictions, extraterritorial jurisdiction (ETJ) and corporate limits of Wake County’s twelve core municipalities: Apex, Cary, Fuquay-Varina, Garner, Holly Springs, Knightdale, Morrisville, Raleigh, Rolesville, Wake Forest, Wendell, and Zebulon. Cross-jurisdictional analysis enhances the value of the analysis. The resultant data are a valuable resource for supporting efforts in environmental management, resource conservation and sustainable development.

Canopy assessments take the Tree Canopy data from the land cover analysis and extrapolate additional information such as canopy type, canopy health, canopy change and canopy benefits.

Canopy type separates tree canopy into two distinct categories: deciduous trees and coniferous trees. Deciduous trees generally lose their leaves in the winter while coniferous (or evergreen) trees generally retain their leaves year-round. Wake County’s overall canopy type composition is 70.5% deciduous 29.5% coniferous.

The study utilized near-infrared imagery to assess foliar health. The analysis allows for identification and targeted investigation of select areas, which helps inform proactive tree maintenance in public areas (greenways, parking lots, etc.) or along major road corridors utilized by first responders, a key aspect of an emergency preparedness plan. Wake County’s trees are assessed to be in predominantly good condition .

To measure the temporal change of Wake County tree canopy, DRG performed a second land cover analysis utilizing 2010 NAIP imagery. The data then allowed for measurement and comparison of Wake County’s tree canopy over the ten-year span from 2010 to 2020.

From 2010-2020, Wake County lost 11,122 acres of tree canopy - a total land area more than double the size of William B. Umstead State Park. The loss represents a 3.6% decrease in the total amount of countywide canopy and a 2% decline in canopy cover relative to overall land cover. Over one-quarter of all block groups lost more than 5% of tree canopy. Mapping canopy change by census block group illustrates the geographic distribution of canopy gains and losses throughout the county. Most of the county’s 597 census block groups experienced net canopy loss during the ten-year period of study.

Wake County’s tree canopy has a combined estimated value greater than $3.2 billion.

Carbon Storage

Trees are carbon sinks; they absorb carbon dioxide from the atmosphere and convert it into glucose, which is used as food for the tree. The leftover carbon is then stored within tree tissue, including the trunk, branches, leaves, and roots. Over their lifespan, Wake County’s trees are estimated to have collectively removed and stored over 10.2 million tons of carbon from the atmosphere. The value of this stored carbon equates to more than $1,742,000 billion.

Trees provide a myriad of community benefits that positively impact the environment and overall human health and well-being. The Wake LCA/TCA specifically examined the ecosystem service functions of tree canopy: air pollution removal, carbon sequestration, and stormwater capture. Collectively, these three service areas hold an annual value of $1,458,859,441.

Each year Wake County’s trees provide:

Air Quality Improvement Remove 11,022 tons of pollutants from the air.

Carbon Sequestration Absorb 414,710 tons of carbon dioxide (CO2).

Water Quality Improvement Intercept 8.1 billion gallons of stormwater (this is about equal thirty times more than the amount of water the flows over Niagara Falls in one hour!)

Operationalizing Data

 Tree Keeper  provides tools, data, and resources to guide future urban forest management and reforestation efforts. This platform can conduct priority planting analyses, insights on future tree canopy projections and ecosystem benefits.

A special thanks to the Wake County Board of Commissioners and Davey Resource Group