Fire is as much a part of nature as rain or wind. Life on Earth has evolved in its presence. In fact, fire plays a critical role in the health of many ecosystems. Managed fires can be constructive, reducing dense vegetation and improving wildlife habitat. Accidental, out-of-control fires can be very destructive.

   Sometimes, the National Park Service and other government agencies intentionally cause fires, called prescribed burns. Before they decide to do this, they carry out numerous studies to determine the potential benefits and harm from burning each acre in a given area. Sometimes, these agencies manage naturally ignited fires. One of the main reasons to allow a managed fire is to prevent a raging fire in the future. When dead trees, twigs, grasses, and other decaying matter accumulate, they may ignite, burn intensely, and spread rapidly.

Controlled fires can encourage new plant growth, which nourishes herbivores, that in turn feed predators. They can also remove invasive species, and encourage the return of native plant species, especially those with seeds adapted to fire cycles. In addition, fires can recycle nutrients that would otherwise be trapped in plant matter and provide improved conditions for the reproduction of some species.    Although prescribed burns can spread beyond control—as happened in Los Alamos, New Mexico, in May 2000—that happens very rarely. The Park Service has conducted thousands of prescribed burns, of which fewer than 50 have escaped control.

   The greatest risk of wildfires remains human activities. Approximately 90 percent of wildfires are started by people.