Tree Care and Maintenance

Seasonal Tree Care Tips: Summer 2020
Retaining and Creating Snags for Wildlife  

Images courtesy of: Cheryl Uchida. A snag in the front yard of a local residence right here in Lake Oswego.

Snags are standing dead trees and an important element of a healthy ecosystem. They provide roosting sites for birds and bats, denning sites for mammals, reptiles and amphibians, food storage areas for woodpeckers and squirrels, food for insect-eating birds and mammals, and critical nesting sites for nearly 40 species of birds west of the Cascade Mountain Range. Snags are a limiting factor for wildlife in urban and residential areas, but more and more, arborists are working with homeowners to retain or create snags where it can be done safely.

Dead and dying trees, and trees with peeling bark, cavities, decay fungi and other parts typically termed “defects” can provide tremendous wildlife benefits. Individual wildlife species have preferences for different habitats, so a wide variety of hardwoods and softwoods, short and tall snags, and small and large cavities scattered across a landscape is most beneficial. Don’t think you have to have a giant dead tree in your yard to provide valuable wildlife benefits. Some species, like chickadees, prefer short snags or tall stumps.

While large over-mature trees tend to have more defects and structural complexity, all trees are potential wildlife snags. Innovative arborists concerned about the loss of wildlife habitat in urban forests have developed thoughtful approaches to creating snags from live trees by mimicking natural succession. Some techniques involve girdling branches or tree trunks, reducing trunk height and creating a jagged top, drilling holes, cutting out cavities, and forming roosting slits.

Dead trees are not necessarily dangerous, but the potential for failure will increase as the tree decays over time. A general rule of thumb for managing risk potential is to reduce the height of the snag to at least 1.5 times the distance to a potential target (i.e. people or property that could be injured or damaged if the tree or part of the tree were to fail). For example, if you are considering retaining a snag located 50-feet from your home, reduce the height of the snag to no greater than 40-feet. Have your snag inspected by a qualified arborist periodically to help manage risk potential.

The Tree Code allows the City to require snag creation as a condition of approval for certain tree removal permits, most often for trees located in Sensitive Lands. The City’s contract arborist looks for other opportunities to suggest snag retention or creation to applicant’s that have received a tree removal permit. Moreover, some local residents are preserving wildlife trees on their own and helping to raise awareness about the critical need for snags in the urban landscape. In doing so, they find joy and excitement in watching wildlife visit and utilize the snag all year long.

The next time you’re considering removing a tree because it is dead, dying or has defects that you’re concerned about, consider working with an International Society of Arboriculture Qualified Tree Risk Assessor to explore opportunities to retain or create low risk snags for wildlife on your property. Feel free to contact the City’s Planning Department at to determine whether or not a tree removal permit is needed prior to creating a snag since all trees measuring at least 6-inches in diameter are regulated by the Tree Code.

Visit these sites to learn more about retaining and creating snags for wildlife:

Snags – The Wildlife Tree. The Importance of Snags in Your Neighborhood, a Living with Wildlife article published by the Washington State Department of Fish and Wildlife, 2011.
A Snag in the Plan, an article by Tom Costello in the November 2013 Portland Audubon Newsletter, pages 8-9.
Arborists and Wildlife: Retaining Trees for Wildlife Habitat, an article by Brian French published in the February 2018 edition of Arborist News. 

Please check back for more seasonal tree care and maintenance advice!

 Please check back for more seasonal tree care and maintenance advice!

Link to Tree Care and Maintenance Archives


Spring 2020: Mulch: Numerous Benefits and Easy Application

Winter 2020: Tree Planting: To Stake or Not to Stake?

Fall 2019: Insects and Diseases

​Summer 2019: Drought Stress Revisited

Spring 2019: Trees and Construction

Winter 2019: Topped Tree

Fall 2018: Autumn Leaves

Summer 2018: Emerald Ash Borer

Spring 2018: Pruning Young Trees

Winter 2017: Tree Related Storm Damage

Fall 2017: New Tree Selection and Planting

Summer 2017: Trees and Turfgrasses

Spring 2017: English Ivy Removal

Winter 2017: Recognizing Tree Risk

Summer 2016: Drought Stress

Fall 2016: Preparing Trees for Winter


Additional Tree Care Resources:

National Arbor Day Foundation The Morton Arboretum
Oregon Department of Forestry Tree Care Info
ISA Find an Arborist Oregon Community Trees
Oregon Department of Forestry Alliance for Community Trees


Right Tree in the Right Place

Use this handy guide for assistance in choosing the right species of tree based on the constraints of a site, such as overhead wires, narrow plant strips, and proximity to structures.

"Right Tree Right Place" - helpful information such as "Use this guide for assistance in choosing the right species of tree based on the constraints of a site, such as overhead wires, narrow plant strips, and proximity to structures."

"Master Plant List" - a guide to the plants that are acceptable for mitigation requirements in Lake Oswego.