Defensible Space and Fuels Mitigation for Arborists and Landscapers

Information

PF&R and Portland Parks Bureau give tips and recommendations to arborists and landscapers on how to effectively mitigate fuels in the Wildland-Urban Interface.

Fuels Mitigation Recommendations in Wildfire Hazard Zones

Lush and natural vegetation is part of Portland's charm and is one of the things that makes our city beautiful and livable. However, our wildland environment creates significant fire hazards, threatening lives and property. The abundance of plant life provides fuel to burn; and our steep topography, combined with seasonal hot and dry winds, allows fire to spread rapidly.

The growing potential of wildfires in our area is very real, and it’s crucial for a home to be protected by creating defensible space. This is an area that surrounds a home and other structures with a buffer zone of protection from the surrounding wildland area. The defensible space is a scientifically proven tactic that slows or stops the progression of wildfire spread and protecting the home from heat, flames and embers too. This also assists firefighters by providing a safer area to protect a home from wildfire as well.

Portland skyline and WUI neighborhood — A view of Portland from the south, featuring a WUI area in the foreground.

The video below outlines steps that can be taken by the homeowner, arborists or landscapers to prepare a home or property in the Portland area for wildfire season. Creating defensible space in the immediate, intermediate and extended zones around a home is vital in protecting the home in the event of a wildfire.

Defensible Space

Maintaining a cut lawn, removing dead plant material and downed limbs are some of the simple steps to follow to maintain a healthy landscape around the home. Yet, there are additional items that may need attention to create the defensible space.

There are three zones around the home that defensible space work can be done. The Immediate Zone (0-5 feet), Intermediate Zone (5-30 feet) and Extended Zone (30-100 feet).

defensible spaces of 5, 30 and 100 feet around a home in the WUI

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Immediate Zone (0-5 feet)

Clear of combustibles and debris
Trimming back trees to 10 feet from roofline, attached garages and decks
Provide non-combustible landscaping
- Remove all flammable duff layers down to mineral soil before adding non-combustible landscaping such as river rock, etc.
Recommend removing vegetation next to home or trimming plants away from home and up from the ground to create a “bonsai” look to create clearance between the ground vegetation and branches/leaves.
Replace plants such as arborvitae, bamboo and juniper, etc. with low-growing fire-resistive plants. These types of plants burn easily and will create a pathway to carry a fire to the home.
Trim back vegetation from wood fencing attached to a home to protect from fire. Recommend clearing a space down to mineral soil around the wooden fence that is 1 ½ times the height of the surrounding vegetation (fuel).
Firewood should be stored 30 feet away from the home.

Intermediate Zone (5-30 feet)

Clear any vegetation from under stationary propane tanks. It is recommended to have cleared space down to mineral soil around and under the tank at least 3 feet in all directions.
Consider creating fuel breaks to break up the continuity of the fuel. This can be accomplished by installing and maintaining trails and walkways that are non-combustible (1/4 minus or decorative rock).
Maintain lawns and native grasses to a maximum height of 4 inches.
Remove ladder fuels from under trees that can carry the fire from the forest floor up into the trees. This includes plants such as ivy, saplings, brush, blackberries, clematis, and low hanging branches.
Limit trees and shrubs to clusters – islands of vegetation. Limit planting to islands of low growing, native, fire resistive plants.
Trees are recommended to have a minimum of 18 feet between the crowns of other trees.
Recommend trimming up limbs on the trees to provide 6-10 feet of clearance between the branches and the ground. Remember to measure from the end of the limb, away from the trunk of the tree.
Recommend removing all dead or dying trees and vegetation.

Extended Zone (30-100 feet)

Consider removing large accumulations of ground cover and debris.
Consider removing all dead or dying trees and vegetation.
Trees within 30-60 feet of a home should have a minimum of 12 feet separation from the crowns of other trees.
Consider removing all ladder fuels that can carry the fire from the forest floor up into the trees. This includes ivy, saplings, brush, blackberries, clematis and low hanging branches.
Consider installing and maintaining fuel breaks like trails and/or roads.

Interested in Learning More?

Portland Fire and Rescue is working to bring a course on defensible space and home hardening to the area targeted at landscapers, arborists and contractors. The course is called “Wildfire Home Protection Strategies,” and was developed by Oregon State University Fire Extension Service, the Oregon Department of Forestry, and the Oregon Department of State Fire Marshal. It is a free, 4-hour workshop focused on reducing wildfire risk around homes, and topics include fire science, defensible space, landscaping, and building modifications.

Please send us your contact information if you are interested in participating, and we will place you on our list.

Send your interest in attending the course to Kim.kosmas@portlandoregon.gov

Please put the "Wildfire Home Protection Strategies Course" in the subject line. Include your name, phone number, email, organization or business name and/or website (if applicable) in the main body of the email.