Although it is desirable to consider watersheds as a whole in relations of forest practices, there are practical and conceptual difficulties in doing so. These arise from several resources: Mass wasting, surface erosion, hydrology, riparian, stream channel, fish habitat, water quality, water supply etc. Watershed ecosystems involve a complex dynamic between many watershed and biological processes operating at many spatial scales, the physical and biological characteristics of a watershed and sub-areas within it reflect the local geology, terrain, climate, vegetation and so on. Because of these differences in landscape features, the sensitivity of watersheds and sub-areas within them to forest practices also varies from lace to place. Watershed analysis is a principle but not an exclusive section of the forest practice rules that addresses cumulative watershed effects.