Bracket Fungus
Ganoderma sp.
This group of shelf fungi were found on the trunk of a dead Fremont Cottonwood (Populus fremontii) along Sycamore Creek in the Mazatzal Mountains of eastern Maricopa Co., Arizona, USA. The fungus itself now has died and will be food for a variety of other organisms such as beetles and mites.
Over the life of a large tree like Fremont Cottonwood (Populus fremontii) a huge quantity of energy, food and nutrients are manufactured (via photosynthesis) and stored. When the tree dies this huge resource becomes available to the biotic community to be used, however, because these resources are primarily in the form of highly stable cellulose and lignin, only those organisms that have the special biochemical tools to unlock these compounds can use them. Fungi are among the most important of these organisms.
The bracket or shelf of the fungus that appears on the outside of a decaying tree is just a small portion of the fungus that was growing as a threadlike matrix of hyphae within the trunk. The shelf fungus is the reproductive arm that produces the spores to be disseminated into the habitat and distributed by wind and animals.