As we mentioned in the Government House, -- in most jurisdictions of the Puget Sound metropolitan area, whether on private or public property - near "wetlands" or shorelines ALL work on steep slopes (greater than 40% grade) usually requires some kind of permit. In new building and utility construction, tree and vegetation removal often gets rolled into the master permit. In the absence of new construction, tree and vegetation removals on in ECA's usually require permitting also. The process for acquisition such permits usually requires some kind of restoration and management plan implemented by the property owner following removal.

The restoration plan consists, primarily, of new tree and plant replacement schedules. The plan may also include remedial measures for drainage, erosion control, wildlife protection, public safety and protection of neighboring properties or public lands from siltation, pollution, or structural damage.

The management plan consists primarily of a multi-year and multi-level maintenance program. Most jurisdictions in which we have conducted ECA-related projects stipulate a minimum three-year period to maintain new trees and plants, drainage systems, erosion control, and other installations required by the ECA permit. Maintenance of the replacement trees and vegetation during this "establishment period" requires primarily, irrigation, weed control, and some level of survival (75% or higher) of the new stock. Staking, incidental pruning, or fertilization may also be required. Many agencies will allow no more than a 10% mortality at the conclusion of the establishment period.

In the last ten years, both new land development and in-fill housing has intensified in cities and suburbs. Increased development density on or even nearby wooded (or formerly wooded) hillsides has often resulted in destabilization and landslide. Improper drainage, dispersal, or disposal of storm water on existing buildings and roadways has also contributed to landslide problems, as has neglect of properly constructed and installed systems. Even with ECA codicils and new ordinances drafted in the early 1990s, threats to the surface and structural integrity of slopes wooded or barren have remained acute.

Whether endeavoring to execute a tree removal project on an undisturbed slope, or rebuilding and restoring landslide gashes, certain fundamentals require attention: drainage and protecting existing understory trees.

Basically, whenever and wherever alteration of an established drainage system results in an over-concentration of water on a slope, the potential for landslide always exists. Combined with reckless removal or destruction of hillside vegetation, landslide becomes inevitable.

In some situations, one or more large trees on a steep hill, pitching and twisting in heavy wind on saturated soil, will uproot and consequently cause a landslide. This phenomenon complicates and confuses the issue of trees on slopes, especially when adjacent trees of the same age and species remain standing firmly rooted upon the hill. Sometimes root crown excavation and soil structure analysis can help predict such failures. Any comprehensive, thoughtful plan for hillside tree removal and subsequent restoration has to take such potential hazards into account.