Natural or human-caused fires that burn forest vegetation. Foresters usually distinguish three types of forest fires: ground fires, which burn the humus layer of the forest floor but do not burn appreciably above the surface; surface fires, which burn forest undergrowth and surface litter; and crown fires, which advance through the tops of trees or shrubs. It is not uncommon for two or three types of fires to occur simultaneously. Fire management programs are extensive in the U.S. and other countries. Programs include fire prevention, fire fighting, and the use of fire in land management.