HomeMy WebLinkAboutPlanning 2013-06-24 F - Special Joint Work Session: Urban Tree Canopy AssessmentCity of
Tukwila
Washington
Urban
Tree
Canopy
Assessment
December, 2012
DAVEY.
REi00ICE GIIIP
City of Tukwila, Washington
Urban Tree Cano py Assessment
September, 2012
Prepared for:
City of Tukwila
6300 Southcenter Blvd., Suite 100
Tukwila, WA 98188
Prepared by:
Davey Resource Group
A Division of The Davey Tree Expert Company
7627 Morro Road
Atascadero, California 93422
Phone: 805- 461 -7500
Toll Free: 800 - 966 -2021
Fax: 805- 461 -8501
www.davey.com/drg
Acknowledgements
This project was made possible by a grant from the Washington State Department
of Natural Resources Urban and Community Forestry Program
(www.dnr.wa.gov/urbanforestry).
Executive Summary
Trees and urban forests are vital to the health and sustainability of any community. Located in
the lushly forested Pacific Northwest, Tukwila recognizes the benefits of trees and the value of
urban tree canopy. While trees have been long appreciated for their contributions of shade and
beauty to our landscapes, science and technology have now made it possible to quantify the
environmental benefits to energy savings, cleaner air and water, carbon dioxide reduction,
property values, and socio - economics. The Center for Urban Forest Research (CUFR) estimates
that over a 40 -year period 100 urban trees in the Pacific Northwest provide $202,000 in benefits
(Trees in Our City).
Tukwila has been a Tree City, USA for over ten years, developing many programs to restore and
maintain the community forest, including sensitive areas restoration, planting trees in parks, and
street tree planting, among others. These activities show that the City of Tukwila has made a
commitment to protect and manage the community's tree resources. As a part of this
commitment, and as preparation for updating the City's Comprehensive Plan to improve urban
forest management, the City contracted with Davey Resource Group in June 2012 to carry out an
urban tree canopy assessment. The purpose of the assessment is to quantify and map existing
urban tree canopy as well as impervious surface, open water, pervious surface, and bare soil.
To accomplish this, high - resolution aerial imagery and infrared technology was used to remotely
map tree canopy and land cover over the city limits. The results of the study provide a clear
picture of the extent and distribution of urban tree canopy over the Tukwila area. The data
developed during the assessment will become an important part of the City's GIS database and
provides a foundation for developing community goals and urban forest policies. The primary
purpose of the assessment was to establish a benchmark value to measure the success of long-
term management strategies over time.
The assessment determined that Tukwila has a current overall average tree canopy cover of 25 %,
and impervious surface of 51% (Table 1). This may be influenced by the fact that, unlike many
communities, Tukwila features more acres of commercial and industrial zoned land than
residential areas. While these businesses are vital to the economic well -being and sustainability
of the community, commercial and industrial zones are simply less conducive to developing and
maintaining tree canopy than residential zones. The residential zones host a range of 33% - 51%
canopy across 1,869 acres, while the industrial and commercial zones have a range of 9% - 49%
canopy across 2,780 acres.
Land Cover Class
Acres
Percent
Canopy
1,615.77
25%
Impervious
3,241.86
51%
Pervious
1,131.67
18%
Bare Soil
1,07.6
2%
Open Water
299.21
5%
Total
6,396.11
100%
Table 1— Percent Land Cover Class Citywide
Tukwila, WA
Urban Tree Canopy Assessment iii