More info: Filtration Erosion Snags

Vegetation helps the soil to absorb water and slow run-off from rain and snow-melt.  Roots hold the moisture-absorbing,fertile topsoil in place during run-off and flooding.   A diversity of root depths and species also provide habitat for bacteria and insects which keep the soil healthy and fertile, thus allowing for faster regeneration of trees and other plants.   Vegetation provides a leafy cover that helps keep the soil and water temperatures at healthy levels, acting as both a source of shade in the summer and insulation in the winter. 

Vegetation is important both dead and alive. Standing dead trees, known as snags, provide shelter for a vast variety of animals, such as racoons, porcupines, squirrels, woodpeckers, bats and owls. Fallen trees provide breeding ground for insects, a vital part of the forest food chain and help to repenish nutrients in the soil. In streams and rivers, vegetation helps to provide fish and other aquatic species with shelter from predators and provides habitats for the insects that provide the main source of food for salmon and other fish.