The Jack Pine and Fire
The jack pine tree of Canada has several qualities that seem to equip it for a life with fire.As in many conifer trees,the branches nearer the ground tend to die off as the tree grows taller,not least because they find themselves without light.In the jack pine,however, these dead branches simply fall off.If the dead branches were allowed to persist,they would provide a “ladder”for the fire from the ground to the top.The physics of fire is in many ways counterintuitive. Crucially,a hot fire that burns itself out quickly can be less damaging than one that’s somewhat cooler but lasts longer.Jack pine needles are high in resin (a flammable organic substance secreted by trees) and often low in water,especially in the droughts of spring and summer when fires are likely,and so they burn hot but quick.On much the same principle,the jack pine’s bark is flaky.It picks up surface fires but then burns swiftly and does little harm.The stringy bark of eucalyptus trees in Australia,hanging loosely from the smooth trunk beneath,is protective in much the same way.In both cases the discarded bark prevents the fire from seriously harming the tree.
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