Trees tend to be long-lived, some reaching several thousand years old.In looser definitions, the taller palms, tree ferns, bananas and bamboos are also trees.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.Certain monocots may be considered trees under a slightly looser definition; Trees have modified structures such as thicker stems composed of specialised cells that add structural strength and durability, allowing them to grow taller than many other plants and to spread out their foliage.They differ from shrubs, which have a similar growth form, by usually growing larger and having a single main stem; made more confusing by the fact that trees may be reduced in size under harsher environmental conditions such as on mountains and subarctic areas.
A new layer of wood is added in each growing season, thickening the stem, existing branches and roots.
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.
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.
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.