A New Path of Conservation Mowing on the Chief Sealth Trail

By Heidi Asplund, Seattle City Light Arboriculturist

Savannah Sparrow at Chief Sealth Trail (Photo courtesy of Ed Newbold)

In 2019, Seattle City Light embarked on a new Conservation Mowing Pilot Program in one of its transmission corridors—areas where high voltage transmission power lines and towers run to connect substations to residences. The Chief Sealth Trail, a 4.5-mile trail popular with pedestrians and bicyclists, is located within the corridor selected for conservation mowing.

City Light’s Vegetation Management Group had long maintained this urban multi-use corridor by mowing it end-to-end throughout the spring and summer months. However, in 2019 and 2020, vegetation managers delayed the timing of the mowing to support bird and pollinator habitats. Most sections of the corridor are mowed end-to-end by late fall.

Because of its many uses, this corridor presents an interesting challenge. City streets run though it in several areas, making visibility for motorists and bicyclists a priority. Additionally, Seattle is an Urban Bird Treaty City and a Bee City USA, designations which reflect its residents’ passion for the natural world.

Balancing the needs of trail users, city residents, and wildlife, City Light developed the following mowing program in partnership with the Seattle Department of Transportation (SDOT) and Seattle Fire Department (SFD):

March through July

  • Limited mowing in the following areas to promote public safety:
    • Transmission tower bases
    • 10-foot buffers off adjacent property lines/fences
    • 3-foot buffers on either side of the Chief Sealth Trail
    • 10-foot buffers at all street-ends and crossings
Conservation mowing map on the Chief Sealth Trail

August through September

  • Mowing after July 31 at the end of local primary bird nesting season:
    • Remaining areas in transmission corridor
  • Re-mowing previously mowed areas as needed

The new mowing program is already showing positive results for the natural habitat. In late March 2020, a well-known Seattle birder announced he had spotted several Savannah Sparrows—migratory ground-nesting birds—along the Chief Sealth Trail. He attributed their presence to the 2019 mowing change, which provided a better habitat for this species. A City Light staff member took GPS data points of Savannah Sparrows observed in the corridor and produced a map to help mower operators avoid potential nests.

At the end of the 2020 mowing season, vegetation management staff will assess the Conservation Mowing Program’s successes and failures and adjust next year’s program accordingly. The hope is to eventually develop partnerships and garner resources to expand the Conservation Mowing Program to include planting and maintaining low-growing native plants for pollinators, birds, and the community’s enjoyment.


Note: This post is adapted from the article “Seattle City Light’s Vegetation Management Group Travels a New Path: A Brief Look at a Transmission Corridor Conservation Mowing Program” by Heidi Asplund, published in the Sept./Oct. 2020 issue of Utility Arborist Association’s Utility Arborist Newsline (Vol. 11, No. 5, pp. 46-47). It is republished here with permission.