Managing Giant Sequoia Surface Roots to Reduce Playground Hazards in Mercer Island

Large surface roots from the mature giant sequoias had begun lifting above the surrounding grade within the playground, creating uneven areas and potential tripping hazards.

PROJECT OVERVIEW

Two mature giant sequoias growing within a Mercer Island playground had developed prominent surface roots in an area regularly used by children, creating an uneven walking and play surface and a potential tripping hazard. Simply cutting or grinding every exposed root was not an appropriate solution: large structural roots play an important role in a tree’s stability and health, and removing the wrong roots, particularly close to the trunk, can create a much larger problem than the one being addressed. The goal was to reduce the surface-root hazards while preserving the health and structural stability of both sequoias.

OUR APPROACH

Seattle Tree Care developed a two-step approach beginning with air-spade excavation. Rather than cutting roots based solely on what was visible at the surface, the crew used compressed air to carefully expose the root system approximately 2–4 inches below grade, identifying the size, location, and configuration of larger roots within the trees’ drip zones, with special attention to areas around playground equipment. The assessment established an important preservation boundary: roots within five feet of the trunk and root flare would be left undisturbed.

Once the root structure was visible, the team made targeted decisions rather than treating every exposed root the same way: smaller surface roots outside the critical area were selectively pruned where appropriate, larger surface roots creating significant grade changes were carefully reduced where it could be done without unnecessarily compromising the trees, and roots close to the trunk and root flare were intentionally protected. Roots don’t always grow exactly where they appear to from the surface: air excavation gives an arborist a clearer picture of the root system before making irreversible cuts, treating the root system as part of the living tree rather than simply “removing the roots that are sticking up.”

Using an air spade, arborists carefully removed compacted soil from around the roots with compressed air rather than digging equipment. Larger structural roots and those near the trunk were preserved.

THE RESULT

The work addressed problematic surface roots in high-use areas of the playground while deliberately protecting the trees’ critical root zones. The project demonstrated that tree preservation and site safety don’t necessarily have to be competing objectives: through air-spade excavation and selective root management, the crew addressed specific trip hazards without unnecessarily removing two established giant sequoias from the landscape.