Fire as a gardener
Why Do Some Forests Need to Burn?
Some forests evolved with regular fire, and stopping it entirely makes the eventual fire far worse.
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Step 1 of 5
Some forests have burned regularly for ages.
In dry pine and eucalyptus country, lightning has started fires every few years for millions of years, long before people arrived.
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Step 2 of 5
The trees adapted to survive small fires.
Thick bark protects the trunk, low branches are shed, and growing points sit high above the flames of a fire running through litter.
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Step 3 of 5
Some seeds actually need the fire.
Certain cones are sealed with resin that only melts in a fire, so the seeds are released precisely when the ground is cleared and fertile.
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Step 4 of 5
Preventing fire lets fuel pile up.
With every small fire stopped, dead wood and litter accumulate for decades instead of being cleared every few years.
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Step 5 of 5
Then the fire that comes is unsurvivable.
Enough fuel lets flames climb into the canopy, and a crown fire kills even the thick-barked trees that would shrug off a floor fire.
Many forest services now light deliberate small fires in cool weather, precisely to stop fuel reaching dangerous levels.
The short version
Some forests evolved with regular small fires, and suppressing them lets fuel build until the eventual fire is hot enough to kill everything.
Try it yourself
Look up photos of a giant sequoia trunk. The fire scars are from fires the tree survived, sometimes dozens of them.
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