Nurse trees are large, fast-growing trees which provide shelter to smaller trees and plants as they grow. These trees are a critical part of forest ecology all over the world, from the Amazonian rain forest to the tangled Alpine forests of Europe, and they are also ecologically important in some other regions, like the desert. In addition to being seen in the wild, nurse trees are also sometimes used by gardeners who want to protect young plants in the early stages of growth, to ensure that they end up strong and healthy.
Several types of protection are provided by a nurse tree. The first is shelter from the sun, and distraction from predators, with many insects and similar predators preferring to feed on larger nurse trees. Nurse trees also shelter younger plants from wind and sand or dust storms, and they attract larger predators like deer, allowing the tender new growth of young plants to remain unmolested.
Eventually, a nurse tree will die, allowing the younger tree to grow up. In a natural forest, the dead tree would be allowed to decay naturally, contributing to the buildup of organic material in the forest and providing nutrition and shelter to numerous plants and animals. In managed forests, deadwood is often cleared out to reduce the risk of fire, and as a result, the forest tends to be less dense and less diverse, because fewer species find an environment in which they can thrive.
In a forest, a nurse tree may be of a different species than the younger plant or tree, or it may be the same species. It is not uncommon to see several plants competing for the space and resources under nurse trees, with one plant eventually choking the others out by exploiting resources adroitly. Outside of forests, nurse trees are used by plants like the saguaro cactus, which roots and spends its young life in the shade of a nurse tree before eventually killing the nurse tree off by taking the majority of the available resources.
Gardeners sometimes create their own nurse trees by planting tender young plants in the shelter of a well-established tree. The mature tree shelters the plant until it is big enough to thrive on its own, and gives the garden some texture and depth at the same time. Some plants also prefer shady environments, so in hot, sunny climates, a nurse tree can allow a gardener to cultivate these plants.