Friendly fire

Australia's mountain ash trees are no relation to the mountain ash of Europe and are actually eucalypts. They are one of the world's tallest trees, standing over 300 feet tall. Their tiny seeds are shed from small capsules throughout the year, but down on the forest floor there is little light so they rely on forest fires for their germination. Oil in the bark and leaves of eucalyptus makes it extremely inflammable. The flames singe the seed capsules, causing them to shed their seeds. But when the fire has passed, many of the seeds will have survived under the soil. Since everything else has been destroyed, the seeds now have access to sunshine and grow vigorously. Nourished by the ash, they grow around the charred logs as thick and uniform as a crop of wheat. Within a year they are so tall they can exclude all other species. As the saplings grow they form a dense mat that stops most other seedlings from getting a root hold. Only the giant redwoods of California are taller than the Australian mountain ash, and that may simply be down to the activities of loggers. Indeed, back in the nineteenth century one mountain ash was measured at 435 feet and is the tallest tree ever recorded. Paradoxically, the biggest threat to the mountain ash is a lack of forest fires. In that case they would die of old age and collapse in the forest without ever having seeded.

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