Bigleaf Maple on a Steep Slope: Anchor or Hazard?

Seattle homeowner, 30-ft bigleaf maple on a 12-ft drop-off. Wife fears it pulls the slope down. Arborist says: it's holding the hill.

The Science

• Bigleaf maple (Acer macrophyllum) is recommended for erosion control by WA Dept. of Ecology
• Massive, shallow root system binds slope soil
• Tree weighs 1.5–2 tons—but roots disperse that load

Real Risk

Removing the tree eliminates root reinforcement. Slope failure risk increases after removal, especially in wet winters.

Next Step

If slope movement continues, hire a geotechnical engineer—not a contractor. It may be a systemic issue (subsurface water, soil creep) beyond one tree.