Nurse Logs - dead and decaying trees - play an important role in forest recycling and the food web. In moist environments similar to the Pacific Northwest’s temperate forest; micro- and macro-organisms, fungi and bacteria continue to feed on the dead or decaying wood once it has fallen. The decomposers are breaking down the dead organic matter and recycling the nutrients by releasing it back into the soil or some other substrate (like the nurse log).
In the past, PNW timber companies used to burn unwanted logs after clearcutting a particular area. More recently, logging companies are beginning to understand the importance of leaving these logs to rot as "nurse logs" on the forest floor. These nurse logs act as sponges holding in water during the summer months when there is less precipitation. They are often colonized by young plants (hence the name nurse). A young plants, such as a huckleberry bush, can then use the nurse log as a kind of platform to grow on, above the shaded forest floor.
Various organisms use these nurse logs as a kind of hotel. The wood is comprised mostly of carbon -- which takes a long time to decompose (often taking centuries to do so). Organisms that can eat cellulose (fungi, bacteria, termites, etc) require nitrogen and other nutrients to survive within the log. Animals that bore are creating habitat and space in which other plants can take root and water can be "stored." As the tree decomposes it produces humus. This humus, or duff, forms the top layer of the forest floor and add nutrition back into the surrounding area!
Imagine a Douglass Squirrel scampering through the forest; nibbling on a Samara (maple seed with “wings”). The squirrel accidently drops part of the seed on a nurse log, which provides fertile substrate from the decomposers’ recycled nutrients, and a few weeks later a Big Leaf Maple seedling (or any other tree whose seeds are dispersed locally) has sprouted.