A
TREE is a
perennial plant with an elongated stem, or
trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only
woody plants with
secondary growth, plants that are usable as
lumber or plants above a specified height. In looser senses, the taller
palms, the
tree ferns,
bananas and
bamboos are also trees. Trees tend to be long-lived, some reaching several thousand years old. The tallest known tree, a
coast redwood named
Hyperion, stands 115.6 m (379 ft) high. Trees have been in existence on the Earth for 370 million years. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a woody trunk and branches as a way to tower above other plants to compete for sunlight.
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A tree typically has many secondary branches supported clear of the ground by the trunk. This trunk typically contains
woody tissue for strength, and
vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of
barkwhich serves as a protective barrier. Below the ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil. Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into sugars by
photosynthesis, providing the food for the tree's growth and development. Flowers and fruit may also be present, but some trees, such as conifers, instead have pollen cones and seed cones; others, such as tree ferns, produce
spores instead.
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Trees play a significant role in reducing erosion and moderating the climate. They remove
carbon dioxide from the atmosphere and store large quantities of
carbon in their tissues. Trees and
forests provide a
habitat for many species of animals and plants.
Tropical rainforestsare one of the most
biodiverse habitats in the world. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, and fruit for food as well as having many other uses. In parts of the world, forests are shrinking as trees are cleared to increase the amount of land available for agriculture. Because of their longevity and usefulness, trees have always been revered and they play a role in many of the world's
mythologies.