Trees

A tree is a perennial woody plant. It is most often defined as a woody plant that has secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to 6 m; some authors set a minimum of 10 cm trunk diameter (30 cm girth). Woody plants that do not meet these definitions by having multiple stems and/or small size, are called shrubs. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (375 ft) high.

Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. Trees also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples). Wood from trees is a building material, as well as an energy source in third world countries. Trees also play a role in many of the world's mythologies (see trees in mythology).

The tree has always been a cultural symbol. Common icons are the World tree, for instance Yggdrasil, and the tree of life. The tree is often used to represent nature or the environment itself.

Tallest trees

The heights of the tallest trees in the world have been the subject of considerable dispute and much exaggeration. Modern verified measurement with laser rangefinders combined with tape drop measurements made by tree climbers, carried out by the U.S. Eastern Native Tree Society has shown that most older measuring methods and measurements are unreliable, often producing exaggerations of 5% to 15% above the real height. Historical claims of trees of 117 m (384 ft), 130 m (427 ft), and even 150 m (492 ft), are now largely disregarded as unreliable, fantasy or outright fraud (however, see "Tallest specimens" chapter in Eucalyptus regnans article). The following are now accepted as the top five tallest reliably measured species:

Coast Redwood (Sequoia sempervirens): 115.55 m (379.1 ft), Redwood National Park, California, United States

Coast Douglas-fir (Pseudotsuga menziesii): 99.4 m (326.1 ft), Brummit Creek, Coos County, Oregon, United States

Australian Mountain-ash (Eucalyptus regnans): 97.0 m (318.2 ft), Styx Valley, Tasmania, Australia

Sitka Spruce (Picea sitchensis): 96.7 m (317.3 ft), Prairie Creek Redwoods State Park, California, United States

Giant Sequoia (Sequoiadendron giganteum): 94.9 m (311.4 ft), Redwood Mountain Grove, Kings Canyon National Park, California, United States

Oldest trees

The oldest trees are determined by growth rings, which can be seen if the tree is cut down or in cores taken from the edge to the center of the tree. Accurate determination is only possible for trees which produce growth rings, generally those which occur in seasonal climates; trees in uniform non-seasonal tropical climates grow continuously and do not have distinct growth rings. It is also only possible for trees which are solid to the center of the tree; many very old trees become hollow as the dead heartwood decays away. For some of these species, age estimates have been made on the basis of extrapolating current growth rates, but the results are usually little better than guesswork or wild speculation. White (1998) proposes a method of estimating the age of large and veteran trees in the United Kingdom through the correlation between a tree's stem diameter, growth character and age.

The verified oldest measured ages are:

Norway Spruce / Picea abies / 9,550 years
Baobab / Digitata Adansonia / 6,000 years according to carbon dating
Great Basin Bristlecone Pine / Pinus longaeva / 4,844 years
Alerce Fitzroya / Cupressoides / 3,622 years
Giant Sequoia / Sequoiadendron giganteum / 3,266 years
Huon-pine / Lagarostrobos franklinii / 2,500 years
Rocky Mountains Bristlecone Pine / Pinus aristata / 2,435 years

Other species suspected of reaching exceptional age include European Yew Taxus baccata (probably over 2,000 years) and Western Redcedar Thuja plicata.

The oldest reported age for an angiosperm tree is 2293 years for the Sri Maha Bodhi Sacred Fig (Ficus religiosa) planted in 288 BC at Anuradhapura, Sri Lanka; this is also the oldest human-planted tree with a known planting date.

*All data from Wikipedia.org