The U.S. Forest Service recommends using only dead and down wood for fires. It also suggests collecting wood away from campsites and using small pieces that can easily be broken by hand. Following these recommendations minimizes impact on the campsite and any nearby living trees.
In the Rain
When it's raining, look for dry wood hanging under down trees. Use your knife to whittle away the wet layers of a stick to get to a dry inside.
Natural Fire Starters
The best wood fire starter is birch bark, which contains oils that burn even when wet. Dry pine needles found near the tree's trunk burn quickly. Black daldinia concentrica, a ball-shaped fungus that grows on dead ash trees, burns like coal when cut open.
Trying an alternative to campfires can lighten your impact on the forest. Consider cooking on a backpacking stove and spending the night under the stars.
To help prevent forest fires, drown all fires and stir the ashes before going to sleep or before leaving the campsite. Make sure the ashes are cold to the touch before you leave.