Like a sponge, from the top canopy layer of a forest to its extensive root systems, water can be either absorbed, held, or released.
As water is absorbed and held by the forest, it reduces the amount of overland runoff that can lead to soil erosion. The severity of flooding, and the amount of sediment washing into rivers, lakes, and reservoirs can be regulated or reduced to some degree by healthy forests. For this reason, logging (particularly near river banks and lake shorelines) can have a very damaging effect.
As this map developed by the U.S. Department of Forest Service shows, only parts of the Northwest contain densely forested areas. Large parts of the Northwest are devoted to agricultural use or are characterized by shrub and scablands.
In addition, forests west of the Cascades are remarkably different from those east of the Cascades. To the west the forest is characterized by damp, foggy sea air, with a long growing season and abundant rain. Areas of deep, dark, ferny forests are the result. Western red cedar and western hemlock thrive in this climate.
As you move inland toward the lower elevations of the Cascades, thick stands of evergreens cover the mountain flanks. At the upper elevations, trees thin out as they fight to survive colder temperatures, thinning soil, and a short, cool growing season. At the higher levels of the mountains, conditions are even more severe within the subalpine forest. Alpine fir and blue spruce are examples of trees in this area.
Because the Cascades form a natural barrier to the large amounts of moisture moving east, forests on the eastern side are quite different. With much less moisture and more extreme climates, these forested areas are more sparse but extremely hardy. The ponderosa pine thrives in this climate.
In all of these forested areas, animals such as deer, bear, elk, birds, squirrels, insects, and a myriad of other species can be found. In streams and rivers, many fish rely on the shade cover of a forested area to cool the water. Also, the woody debris and leaves of trees are very important to the habitat and nutrient needs of salmon and other fish.