Some mushrooms are capable of digesting wood, breaking it down into the primary components of forest soils. They also decay other dead plant and animal matter. A forest in which nothing rotted would soon be choked with accumulating dead leaves and woody material, and starved for essential minerals and other nutrients bound up in the undecomposed debris.
Many mushrooms form partnerships with roots of living trees, and the resulting fungus-root joining is called a mycorrhiza. The mushroom's mycelium weaves itself around the root and actually alters the shape of it. The mushroom absorbs water and minerals for the tree, but in return the tree gives the mushroom nutrients, too. Since both partners benefit from each other, their alliance is considered a symbiotic relationship. Mycorrhizal mushrooms are often seen under trees, growing in lines or rings, following the progress of root growth under the soil.
Many forests support a multi-million-dollar industry based on the commercial picking of edible wild mushrooms. In some forests the mushroom crops are more valuable than the tree crops. The most common mushrooms picked for profit include chanterelles (Cantharellus cibarius), morels (Morchella species), and Ascomycetes (also known as truffles). Many animals also rely on mushrooms for food, especially squirrels and other rodents. Slugs also dine on mushrooms, and certain types of flies spend their whole lives on, and in, mushrooms.
Mushrooms are not always beneficial. The most damaging root disease of conifers in British Columbia is caused by a species of "honey mushroom" called Armillaria ostoyae. Of course, some mushrooms can also have nasty effects on uninformed humans. Every year mushroom poisonings are reported throughout the world. Fortunately, most are not fatal. There is no other way, apart from accurate species identification, to safely tell an edible mushroom from a poisonous one. If you can't have your wild mushrooms identified by an expert - if you are not absolutely sure about which species you have - don't take a chance!
Your local Poison Control Centre should be contacted immediately in the event of a mushroom poisoning (which is usually indicated by discomfort after eating wild mushrooms) or if you suspect that a small child has eaten wild mushrooms. If a trip to the hospital is necessary, try to bring along some uneaten mushrooms so that the species of mushroom can be quickly identified. Be absolutely sure about which species you have - don't take a chance!