In some forests where the trees grow tall such as in the US Pacific Northwest when a giant tree falls, it can clear a patch of forest letting in light and providing a new surface for seedlings to take root, away from the competition of the forest floor.
Sometimes the nurse log is so successful as a sort of creche for the young trees that they will grow along the full length of the fallen trunk. And when the original log decays away it leaves a remarkable, straight line of trees.
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