Portal:Trees
Trees
In botany, 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 wider definitions, the taller palms, tree ferns, bananas, and bamboos are also trees. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight. Trees tend to be long-lived, some reaching several thousand years old. Trees have been in existence for 370 million years. It is estimated that there are just over 3 trillion mature trees in the world.
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 bark which 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.
Trees usually reproduce using seeds. Flowers and fruit may be present, but some trees, such as conifers, instead have pollen cones and seed cones. Palms, bananas, and bamboos also produce seeds, but tree ferns produce spores instead.
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 rainforests are among 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, with sacred groves in various cultures, and they play a role in many of the world's mythologies.
Selected article
Krummholz or Krumholtz formation (German: krumm, "crooked, bent, twisted" and Holz, "wood") — also called Knieholz ("knee timber") — is a particular feature of subarctic and subalpine tree line landscapes. Continual exposure to fierce, freezing winds causes vegetation to become stunted and deformed. Under these conditions, trees can only survive where they are sheltered by rock formations or snow cover. As the lower portion of these trees continue to grow, the coverage becomes extremely dense near the ground.
Common trees showing Krumholtz formation include Balsam Fir, Red Spruce, Black Spruce, Subalpine Fir, Subalpine Larch, Engelmann Spruce, Limber Pine, and Lodgepole Pine. Instances of the Krumholtz form of Black Spruce, Picea mariana, are found in the northern Canadian Boreal forests. Krumholtz-form Black Spruce and Balsam Fir are abundant in the Alpine Transition Zone of the White Mountains of New Hampshire.
Selected biography
Axel Erlandson (December 15, 1884 – April 28, 1964) was a Swedish American farmer who shaped trees as a hobby, and opened a horticultural attraction in 1947 advertised as "See the World's Strangest Trees Here," and named "The Tree Circus."
The trees appeared in the column of Robert Ripley's Believe It or Not! twelve times. Erlandson sold his attraction shortly before his death. The trees were moved to Gilroy Gardens in 1985. Read more...
In the news
Selected images
Palms and cycads as they might have appeared in the middle Tertiary
Common ash (Fraxinus excelsior), a deciduous broad-leaved (angiosperm) tree
Alleé of London plane trees (Platanus × acerifolia) in garden
Lepidodendron, an extinct lycophyte tree
Tall herbaceous monocotyledonous plants such as banana lack secondary growth, but are trees under the broadest definition.
The General Sherman Tree, thought to be the world's largest by volume
Northern beech (Fagus sylvatica) trunk in autumn
Buds, leaves and reproductive structures of white fir (Abies alba)
Diagram of secondary growth in a eudicot or coniferous tree showing idealised vertical and horizontal sections. A new layer of wood is added in each growing season, thickening the stem, existing branches and roots.
Roof trusses made from softwood
Dormant Magnolia bud
Latex collecting from a rubber tree (Hevea brasiliensis)
Conifers in the Swabian alps
Buds, leaves, flowers and fruit of oak (Quercus robur)
People trees, by Pooktre
Yggdrasil, the World Ash of Norse mythology
Form, leaves and reproductive structures of queen sago (Cycas circinalis)
Sugar maple (Acer saccharum) tapped to collect sap for maple syrup
A young red pine (Pinus resinosa) with spread of roots visible, as a result of soil erosion
Trees in art: Weeping Willow, Claude Monet, 1918
Buttress roots of the kapok tree (Ceiba pentandra)
Selling firewood at a market
Recently stripped cork oak (Quercus suber)
European larch (Larix decidua), a coniferous tree which is also deciduous
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Did you know?
- ... that Gregory's tree (pictured), near Timber Creek in Australia's Northern Territory, bears inscriptions by 19th-century explorers and is registered as both a heritage place and an Aboriginal sacred site?
- ... that the Balderschwang Yew is possibly the oldest tree in Germany?
- ... that black truffles suppress plant growth around their host tree, creating an area that looks burned?
- ... that root extracts from the tree species Pycnanthus angolensis can be used to treat parasitic infections, such as schistosomiasis?
- ... that the lime trees of Duncliffe Wood are reputedly among the oldest living things in the county of Dorset?
- ... that trees of the New Guinea genus Finschia have stilt roots coming off the trunk up to 1.8 m (6 ft) off the ground?
- ... that in the early 1980s, a team of surveyors discovered the World War II-era Avro Anson Memorial near Clackline, Western Australia, which had been overgrown by shrubs and trees?
