Long before there were wood chippers or people to run them, fungi have had a critical role in removing fallen logs and other forest debris.   Fungi secrete extracellular enzymes that help to break down the various components of logs, leaves and other debris.   When sufficiently broken down, fungi can take up nutrients from the wood soup created enzymatically.  In this way, fungi grow and reproduce while forests get rid of fallen logs and old leaves.   This photo, however, shows another method that fungi may utilize to break down a log.   The fungi on this old log are growing under the bark and pushing it away from the remainder of the log.   That is, this fungus is using physical pressure in addition to enzymatic processes to breakdown this old log. 

While some fungi are clearly useful, for example the strains we use to bake our bread and brew our beer, all fungi fit into a larger picture.  The fungi pictured here may not be edible (never eat a fungus unless you are certain of the identity), but returning an old log into an organic soil is a service.   And just think how much quieter this fungus is than your average wood chipper! 

Click on the images to see a larger image of Figure 1 or to see other articles on fungus.