Silva's uses an Ecosystem Sensitivity to Disturbance (ESD) rating system to estimate the sensitivity of parts of the landscape to human uses. The rating system is based on a group of physical factors:

• slope gradient
• slope shape or complexity
• soil depth to a water impermeable layer
• site moisture conditions

Map and air photo interpretation, coupled with field assessments, are used to determine the characteristics of the landscape through this rating system. Various combinations of these factors result in high or extreme ESD ratings. Sites which generally receive high or extreme ratings include:

• Riparian ecosystems
• Steep Terrain (slopes greater than 60%)
• Wetlands
• Complex Terrain
• Areas of shallow soil
• Dry sites, such as ridge tops and deep gravel soils
• Areas dominated by avalanche chutes
• High elevation transition forests

Unacceptable losses of ecosystem functioning will result if timber management, road construction, mining activities, or other consumptive resource extraction occurs in areas with a high or extreme ecosystem sensitivity. On the other hand, ecologically responsible timber management, road construction, mining, and other consumptive resource extraction activities are permitted within moderate and low ESD ratings. Such activities can also be carried out in small low and moderate ESD areas located within larger high and extreme ESD rating areas, provided non damaging access methods can be devised.