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Wildfire as Ecology: The Process Some Forests Cannot Live Without

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Wildfire as Ecology: The Process Some Forests Cannot Live Without

This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.

It is tempting to treat wildfire purely as a disaster, and in the places where it threatens human life and property it plainly is one. But across large stretches of the natural world, regular fire is not a disruption of the ecosystem's normal functioning; it is part of that normal functioning, and some species have evolved to depend on it directly. The clearest example is serotiny, a trait carried by the giant sequoia and many pine species, in which the tree's cones stay sealed, sometimes for years, resisting opening under ordinary conditions. Only the heat of a passing fire melts the resin holding the cone shut, releasing the seeds onto a seedbed the same fire has just cleared of competing vegetation and enriched with a fresh layer of mineral-rich ash. A giant sequoia grove that never burns is not a healthy grove left alone; it is a grove that has stopped reproducing.

Grassland and savanna ecosystems depend on fire in a different but equally direct way. Left unburned for long enough, a grassland is gradually invaded by woody shrubs and trees, which shade out the grasses and shift the ecosystem toward forest. Periodic fire, historically both lightning-ignited and deliberately set by grazing animals' own foraging pressure and by human land management, kills back the encroaching woody growth while the grasses themselves, whose growing point sits at or below ground level, survive and resprout quickly, maintaining the open, grass-dominated structure that defines the ecosystem and the grazing animals it supports.

Every fire-adapted ecosystem has its own characteristic fire-return interval, the typical span of years between fires under natural conditions, and that interval varies enormously: some savanna grasslands naturally burn every year or two, while some conifer forests may naturally go many decades or even a century or more between fires. An ecosystem denied fire for far longer than its natural interval does not simply stay safely unburned; it accumulates dead wood, litter and dense undergrowth well beyond what its natural fire regime ever allowed to build up, so that when a fire eventually does arrive, deliberately or by accident, it burns far hotter and more destructively than the smaller, more frequent fires the ecosystem evolved alongside.

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