At best plants will only stabilize the surface soils up to 6% at best. Only good engineering practices will limit the problems partially. Willows,ferns,grasses.... one has to be very carefull planting trees, since they get tall and can fall over making the problems even worse. (I tend to densely plant Cedars, if the soil conditions allow it) Evergreens will give better all season protection.
kome: There is a northfacing slope along River Road between Fort Langley and Glen Valley that is quite steep yet holds together well. On it grow many native deciduous trees which, after they reach about 10 ft. are cut nearly to the ground with steel brush cutters and are allowed to regrow. I believe they leave most of the material they cut where it falls. I've often thought the slope would fail but year after year it remains in good shape and is always interesting to look at. At certain times of the year, you can see many small gullies that excess water has been channeled thru.
I was going to suggest Aapathas. We use these along our earthen drainage gutters. Sometimes the banks are 6 ft drop down to the road. By using the Agapantha rootsystem it stops the soil being washed away from the bank. I also use native plants above this to help stabelise foot track area.. I hava a boundary in the paddock (used to be a ploughed field) that is a 6 foot drop down into the next property that is a very steep block. The old fence witht he help of grass held all this soil so it did not wash down the hill. I have used ginger and agapantha to good effect on my side as well as tree planting and the neighbours covered their hill side in birches. Just another idea. Liz
