Land Cover can generally be considered as the vegetation, water, natural and man-made surface of the earth.
This particular land cover layer was developed as the basis for the County’s 2013 Urban Tree Canopy Assessment (UTC). This high resolution land cover is far more detailed than traditionally available sources. “Patches” of forest were extracted and then generalized from the highly detailed land cover data developed in the UTC study.
Actively maintaining existing trees is more important and more cost-effective than planting new ones. Planting of new trees without an adequate budget for maintaining them is often an inappropriate use of resources. Establishing a tree canopy goal is crucial for communities seeking to improve their green infrastructure. National Forest Service suggests a minimum 41% tree canopy for urban areas as an overall goal; 50% or greater is needed in stream corridors and headwaters.
Tree canopy is the layer of leaves, branches, and stems of trees that cover the ground when viewed from above. In 2013 County Planning conducted did an urban tree canopy (UTC) assessment to help decision makers understand their urban forest resources, particularly the amount of tree canopy that currently exist and the amount that could exist. Potential tree canopy is considered the remaining (non-treed) portion, which could potentially be modified to accommodate tree canopy. These areas include vegetated, bare, and even some paved areas. Note that potential tree canopy percentages may be low in areas containing large amounts of existing tree canopy, and may be relatively high in areas that are largely made up of parking lots.
For forest patches, a simple classification scheme was developed to characterize those patches, primarily by size. The classification scheme is geared towards ultimately identifying habitat planting areas where the establishment of new tree canopy would help to improve wildlife habitat by connecting large patches of tree canopy to smaller spaces nearby. Existing forest patches are classified as:
- Small = Less than 500 sq. ft.
- Medium = 500 – 10,000 sq. ft.
- Large = Greater than 10,000 sq. ft.
Importance and Value
Tree canopy is an indicator of the portion of land covered by trees, usually somewhat mature trees, regardless of whether or not there are built structures such as buildings, sidewalks, or parking lots under the trees.
- Trees and soils function together to reduce stormwater runoff. Trees are living water towers and they rapidly soak up stormwater
- Trees help minimize flooding and improve water quality
- Trees help moderate temperature through shade, windbreaks and cooling through evapotranspiration or the transport of water from soils, plants and water features to the atmosphere, thus reducing the urban heat island effect occurring in city centers.
- Trees remove many pollutants from the atmosphere, including nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO), and particulate matter (PM) of 10 microns or less (PM10).1
- Trees are able to reduce greenhouse gases through the absorption of atmospheric carbon.
- Trees provide diverse habitat, food, and nesting needs for a wide variety of wildlife.
- Contiguous blocks of vegetated land, particularly woodlands, are more beneficial than individual fragments of the same.
- Larger blocks of woodlands and vegetation both provide wildlife habitat and keep wildlife within these blocks, which minimizes their wandering into residential and commercial areas.
Recommendations for Communities and Land Owners
- Protect the existing tree canopy, especially in stream headwaters areas
- Adopt modern tree codes which protect and require trees throughout the community.
- Establish tree removal fees and recompense requirements for identified specimen trees
- Require tree surveys as part of development approval
- Establish a tree planting schedule for publicly owned property, especially for plantable areas which they control.
- Develop a municipal tree maintenance budget. Caring for existing trees is more important and economical than planting new ones without adequate budget to maintain them
- Retrofit parking lots with trees or make tree islands and street trees a part of city code or design guidelines.
- Encourage, even provide incentives for, private property owners to plant and maintain more trees in private property, especially privately held plantable areas.
- Develop citywide plans and practices to minimize the spread of tree diseases and tree killing insects such as the Emerald Ash Borer and Asian Longhorn Beetle and replace affected trees with a diverse palette of resistant species.
- Adopt landscaping design standards relative to trees for commercial and industrial properties.
- Ensure landscape design and planting requirements are environmentally and species appropriate to ensure the health and long-term survival of new plantings.
- Identify areas which could extend or connect forest patches and determine the practicality of planting more trees in these areas.
- Develop programs that educate residents on tree stewardship and provide incentives for tree planting and/or to maintain forest patches on their property.
Resources for More Information
- Forest Service Open Space Conservation Strategy – outlines national priorities to help the Forest Service be a more effective partner in open space conservation to ensure that forests and grasslands across the landscape can continue to provide valued services and benefits.
- For further information, see the County’s full report on its Urban Tree Canopy site and a more complete documentation of the land cover analysis (PDF) performed by the University of Vermont’s Spatial Analysis Laboratory.
- The Downloads section of the UTC provides downloadable GIS and spreadsheet data for several levels of geography, as well as links to live web map services. Each of the downloadable data sets contains great detail on acreage and percentages of all the available land cover measures.
- For background on the topic of UTC Assessments, see the Conclusions and Background sections, both of which include links to additional resources.