Fires set by lightning have always shaped wildland ecosystems. The occasional fire burned unchecked until it ran out of fuel or was doused by rain. The fire opened up the forest canopy, letting in more light. It also cleared undergrowth, allowing new plants to grow. After a major fire, different plants and animals often repopulated the burned areas, bringing biodiversity to the forest.
Some plant species even depend on fire to germinate their seeds.
They burned fields to clear away brush and trees and to produce fertilizer from the ash. This practice is still used in many tropical areas around the world today. About 100 years ago, the U.S. National Park Service adopted a policy to suppress all wildland fires. Whether a fire was ignited naturally by lightning or accidentally by man, firefighters would extinguish the fire as quickly as possible in order to protect the trees and nearby property. But without any fire to clear the twigs, branches, and brush, serious undergrowth began to build up.