I have a large (1 foot+ across) orange fungus growing on the bark of a large oak tree. It is approx. one foot off the ground and has smooth edges.
Could you tell me what it is called? Should I be worried?
From the photo you provided, it appears to be Chicken of the Woods (Laetiporus sulfureus).
Massive clusters of bright sulfur-yellow to salmon to bright-orange, shelf-like fruiting structures that turn white with age initially form in the summer or autumn on the wood of the tree but fall off during the winter. The underside of the fruiting structure has tiny pores in which the spores are formed. New shelves form on the wood the following summer and autumn. The bark where the fruiting structure forms is slightly depressed and cracked.
Fruiting structures form long after most of the damage has been done. Infected trees are very prone to wind breakage even before the fungus begins to form fruiting structures and should be removed at the first sign of infection.
Before deciding to remove the tree, you may want to consult an arborist.