In Botany, trees are perennial plants with slender stems or trunks that support branches and leaves in most species. In some uses, trees may be more narrowly defined, including woody plants with only secondary growth, plants that can be used as wood, or plants that are higher than a specified height. Trees are not taxonomic groups, but a variety of plant species, which independently evolved woody trunks and branches, towering over other plants, competing for sunlight. In a loose sense, higher palms, tree ferns, bananas and bamboos are also trees. Trees tend to live long, some of them can grow for thousands of years. The highest known tree is a coastal redwood called Hyperion, 115.6 m (379 ft) high. Trees have been around for 370 million years. It is estimated that there are more than 3 trillion mature trees in the world.

Trees play an important role in reducing erosion and mitigating climate change. They remove carbon dioxide from the atmosphere and store large amounts of carbon in tissues. Trees and forests provide habitats for many animals and plants. Tropical rainforest is one of the most diverse habitats in the world. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, fruit for food and many other uses. In parts of the world, forests are shrinking as trees are cut down to increase the amount of land available for agriculture. Because of their longevity and practicality, trees have always been respected by people. There are sacred forests in various cultures. They play an important role in many myths in the world.

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