What are the strange growths on this fallen tree?
They are a type of mushroom called a polypore. Polypores are also known as shelf fungi, because they tend to grow out from the tree in woody shelves.
Polypores provide a valuable service to the forest by helping to decompose fallen trees, returning valuable nutrients to the soil. Eventually, this tree and all of the others that fell during Hurricane Ike in 2008 will completely decay and return to the soil to support the growth of other plants and animals.
Like all mushrooms, what you can see here on the surface of the tree is only a small part of the plant. This visible part is the fruiting body of the plant; it is much like looking at the apple rather than the entire tree. The main body, called the mycelium, is inside the dead tree. The mycelium is a complex network of small, string-like cells called hyphae that secrete special chemicals to break down the molecules of wood. Under the influence of specific environmental conditions, the mycelium will produce the visible fruiting bodies.
How did the polypores happen to grow in this dead tree?
A spore from another polypore was carried by the wind and arrived on the dead tree, where it found suitable nutrients and began to grow. The spores are produced by special cells that line the tiny holes, or pores, on the underside of the fruiting body. That is the origin of its name, polypore, which means "many pores."
Polypores are tough and most species are not edible, but they have occasionally been used by people interested in herbal medicine to make tea. Also, artists sometimes use them to carve beads or to make etchings. One species, called the Artist’s Conk, has a pore surface that changes color from cream to brown when bruised, and this allows the artist to create intricate etchings.