Supporting Studies & Maps

Updated: Aug 30, 2019

Tacoma's Tree Canopy Assessment

“ Urban forestry can be defined as the art, science, and technology of managing trees and forest resources in and around community ecosystems for the physiological, sociological, economic, and aesthetic benefits trees provide to society." Helms, 1998

In 2018, the City completed a high-resolution urban tree canopy assessment for a better understanding of the extent of tree canopy and opportunities City-wide.

CITYWIDE URBAN TREE CANOPY

This urban tree canopy assessment utilized the land cover map as a foundation to determine Possible Planting Areas throughout the City. Additional layers and information regarding land considered unsuitable for planting were also incorporated into the analysis.


Results of this study:

6,406 acres (20%) are covered with urban tree canopy

4,064 acres (13%) are covered with low vegetation where it's possible to plant trees (PPA) 21,006 acres (67%) are considered unsuitable for tree planting

The following summarizes the tree canopy assessment results by land use:


DATA SOURCES

This assessment utilized 2017 high-resolution (1-meter) multispectral imagery from the U.S. Department of Agriculture’s National Agriculture Imagery Program (NAIP) and 2017 LiDAR data from the Washington State Department of Natural Resources to derive the land cover data set. The NAIP imagery is used to classify all types of land cover, whereas the LiDAR is most useful for distinguishing tree canopy from other types of vegetation. Additional GIS layers provided by the City of Tacoma were also incorporated into the analysis.


MAPPING LAND COVER

An initial land cover dataset was to be created prior to mapping tree canopy and assessing change. The land cover data set is the most fundamental component of an urban tree canopy assessment. An object-based image analysis (OBIA) software program called Feature Analyst was used to classify features through an iterative approach. In this process, objects’ spectral signatures across four bands (blue, green, red, and near-infrared), textures, pattern relationships, and object height were considered. This remote sensing process used the NAIP imagery and LiDAR to derive five initial land cover classes. These classes are shown below.


Five (5) distinct land cover classes were identified in the 2017 tree canopy assessment: urban tree canopy, non-canopy vegetation, bare soil and dry vegetation, impervious (paved) surfaces, and water

View the full report at https://bit.ly/2KUQHRR


Urban tree canopy, possible planting area, and area unsuitable for UTC in the City of Tacoma

Urban tree canopy in Tacoma by U.S. Census block groups



The Nature Conservancy's "Outside Our Doors" Report

"Natives of the Puget Sound region have witnessed a place that has changed dramatically in recent decades—in culture, economy, and nature. Today it is a place of contrasts.


This report presents a panoramic view of how our cities and towns benefit from nature—on the streets, next to schools and hospitals, outside our windows; everywhere people are, we can benefit from nature."


View the report at www.washingtonnature.org/cities/outsideourdoors

Written by Erin House, Caitlyn O'Connor, Kathleen Wolf, Ph.D.

Jessie Israel, Tashina Reynolds & Milepost Consulting


From the report:

"This report presents a panoramic view of how our cities and towns benefit from nature—on the streets, next to schools and hospitals, outside our windows; everywhere people are, we can benefit from nature."


"Investments made in bringing nature back into our cities will benefit both the people living here, and the future resilience of the region."


"Even brief contact with nature provides opportunities for restorative experiences."


"Children do not necessarily need 'wild nature' to reap the benefits of contact with the natural world."


"Increased tree and shrub cover near schools has a positive effect on student performance."


"Nature in our daily lives enhances the strength of social ties among neighbors by encouraging use of common spaces."


"Green space & tree canopies considerably boost the market value of homes, thus providing important contributions to the overall property tax base in cities."


"Quality of life, including outdoor recreation amenities, is ranked as one of the main factors when deciding to take a job or relocate a company."


"Investments in green infrastructure generate a broader range of benefits in comparison to traditional grey infrastructure."



TreePlotter Inventory Management Software


TreePlotter map of Tacoma's trees displayed by diameter

The city's TreePlotter web application is a tool that was acquired in 2018 to track existing trees and newly planted trees.

Learn about the trees in Tacoma comprising "One Canopy" and find the tree nearest you! Visit the Explore Our Forest page to zoom and pan the map or use the search (globe) icon to type in your address. Click on the trees, change the legend layer, or use the "Hub" to learn about the types of trees, size of trees, and more!

Examples summaries of the tree inventory data. Provides a list of the 10 most common tree species and a summary of the tree size classes

Urban Heat Island Study


What is an urban heat island?

An urban heat island occurs when a city experiences much warmer temperatures than nearby rural areas. The difference in temperature between urban and less-developed rural areas has to do with how well the surfaces in each environment absorb and hold heat. The more paved surfaces, the greater the potential for urban heat islands.

In 2018, researchers from the Sustaining Urban Places Research (SUPR) Lab at Portland State University visited Tacoma to collect high resolution urban heat data with the help of local volunteers. Tacoma city urban foresters, public health and city planners, and others offered their time and energy to collect the data. Tacoma is one of the five cities chosen for the Canopy Continuum study, which examines the implications of landscape conditions, extreme heat events, and human health. Of the five cities that are part of the study, Tacoma contains the highest canopy cover, middle value of impervious surface cover, and is located in a dry-summer, wet-winter climate – all of which makes it a very important point of study.

Map displaying morning surface temperatures throughout Tacoma


The Urban Forest Management Plan is being developed to provide equal access to the benefits provided by trees. Existing studies such as the urban heat island study provide data to inform recommendations in the UFMP. Additional studies such as the Communities of Concern in 2014, and the 2009 & 2018 Urban Tree Canopy Assessment can be overlayed to identify trends and opportunities. An example of this is shown in the image below:


The map on the left is symbolized to show the Communities of Concern on a weighted color scale and the 2009 tree canopy cover by Census Block Group. The image on the right shows the afternoon surface temperatures. This information will inform tree planting and maintenance strategies to ensure equitable distribution of services and benefits

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Tacoma, WA 98402

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