Slope stabilization using native plants (workshop handout)

Functions of plants for slope stabilization

Plant roots form a fibrous web that stabilizes and anchors the soil.

Roots and residues help maintain soil porosity, increasing infiltration and thus decreasing runoff

Plant cover intercepts rain, reduces the direct impact of rainwater on the ground surface and protects from surface runoff and erosion. Dense groundcovers and grasses reduce runoff velocity and act as a filter trapping soil that would be washed downslope.

Vegetation and associated plant litter filter the transport of soil moisture. Plants can play an important role in dewatering unstable slopes. Soil moisture is drawn up through roots and into plant leaves where transpiration releases it into the atmosphere (mostly works for evergreens).  This delays onset of saturation and runoff.

(notes from online articles by Marcia West, Seattle Daily Journal of Commerce, and the WA Dept of Ecology).

NW Native Plants recommended for slope stabilization

Various willows- deep and wide roots, most in moist soil: Salix lasiandra, S. sitchensis, S. hookeriana; S. scouleriana (tolerates drier soils than other willows). Deciduous, large shrubs to small trees.

Northern Black Cottonwood- Populus trichocarpa- deep and wide, extensive rooting in moist soils. Large deciduous tree.

Cascara- Rhamnus purshiana- deciduous small tree to large shrub, deep rooting. (Like its family member Ceanothus, and like the unrelated Alders and Myricas, it is a non-leguminous nitrogen-fixer.)

Salmonberry- Rubus spectabilis- spreads via underground runners, thicket-forming; deciduous shrub with flowers appealing to hummingbirds and edible berries sought by wildlife.

Snowberry- Symphoricarpos albus- extensive fibrous roots and runners, thicket-forming; drought-tolerant, deciduous.

Salal- Gaultheria shallon- evergreen shrub spreading via runners and extensive fibrous roots to form large thickets with extensive leaf cover.  Edible berries, drought tolerant.

Ocean Spray- Holodiscus discolor- large deciduous shrub with fibrous roots at moderate depth, sprays of white flowers.

Vine maple- Acer circinatum- multi-trunk deciduous shrub with moderately deep fibrous root system; needs moisture to establish. Great fall color in sun; also tolerates shade.

Kinnikinnick – Arctostaphylos uva-ursi-  low shrub spreads sideways, extensive fibrous root system, thick evergreen foliage.  Also, other Arctostaphylos spp.

Thimbleberry- Rubus parviflorus- spreads via underground runners, fibrous roots, to form thickets. Deciduous, drought-tolerant, part shade.  Attractive flowers, bland but edible berries liked by wildlife.  Foliage is browsed heavily by deer.

Indian Plum- Oemleria cerasiformis- tall deciduous shrub to small tree, part shade, spreads via fibrous roots and runners to form stands

Evergreen huckleberry- Vaccinium ovatum- extensive fibrous roots, evergreen shrub, does not form thickets. Attractive landscape element, tasty berries.

Nootka rose- Rosa nutkana- spreads via fibrous roots and runners to form thickets. Typical on bluffs over the Sound, some salt tolerance.

Mahonia nervosa (full shade), Mahonia aquifolium (part shade)- evergreen, fibrous root system

Fragaria spp- Coast strawberry- Fragaria chiloense- spreads rapidly via runners, covers ground, semi-evergreen; also: Fragaria virginiana and F. vesca.