Its action exposes the heartwood, one of the internal layers of the wood formed by cells through which the sap does not circulate. The width of the hole depends on the age and diameter of the tree. They must be wide enough to preserve the layers of wood rich in conductive vessels, mainly the sapwood and cambium, located further outside, under the bark. These holes often serve as a refuge for small animals, fungi and bacteria.
For this reason, in countries like Sweden they fight to conserve plant species to protect the organisms that live in them. In Australia, about three hundred animal species are known to inhabit plant cavities. In California's Redwood National Park, a road loops through the hollow open at the bottom of massive 2,000-year-old redwood trees 7 m in diameter. The trees are still alive and have not lost their lushness.
