In the last couple weeks the news carries stories on erosion, landslides, and mud slides all around the world, not just here in the PNW.  Yet, a walk along beaches, in ravines, or in the mountains, I see many steep slopes that show no signs of erosion. What is the difference between a stable slope and one that that is eroding?  Native plants play a critical role to slope stability. Although presence of a native plant community alone, is not a guarantee a slope will remain stable, it sure helps. The geology and hydrology of a site are other factors that affect slope stability.

 The role of a native plant community is to protect the landscape. The tree canopy stores rain water during a storm event.  Rainfall slowly trickles through the intricate network of leaves, branches, and limbs. Beneath the tree, rainwater is captured in a thick layer of forest duff composed leaves, moss and twigs. The duff absorbs and holding large quantities of rainfall like a sponge. On the ground, deep penetrating roots hold the soil in place. 

Native plant community has three layers that include trees, shrubs, and ground covers.  Each plant in the community plays a different role in slope stabilization. With increasing land development, there is pressure to remove trees and to open views and replace the native plant communities with lawn. But, there are other options. 

 Call a certified arborist to help you create a view corridor. Ask them about pruning techniques that can open views and preserve trees at the same time. Another common practice is to install lawn directly to the top edge of a slope. Lawn installed in this manner may contribute to future erosion problems. To reduce erosion, retain a wide swath of native plants (20 to 50 feet wide) along the top edge of any slope. While grass is a better short term option than bare soil to minimize erosion, its shallow roots cannot replace the benefits of native plant community.

 An effective restoration project should include the replacement of trees, shrubs, and ground covers. To begin a restoration plan, first determine which native plants will grow best in your site. If you have a shady and wet site  plant Western red cedar, salmonberry, vine maple, osoberry, and sword fern. If on the other hand you have a dry site plant Douglas fir, hazelnut, oceanspray, and snowberry. Redtwig dogwood is a great plant for erosion control, it prefers a wet, but sunny location as does the Sitka and hookers willows.

 Restoration is always more costly than preservation. The best approach is to protect existing native plant communities rather than to restore a collapsed hillside. If you have a slope with native plants, tread lightly and preserve it. It is important we begin to recognize the benefits of preserving native plant communities or we will continue to experience more erosion and landslides than nature intended.