botany, an evergreenplant is a plant having leaves all year round. This contrasts with deciduousplants, which completely lose their foliagefor part of the year.
Leaf persistence in
evergreenplants may vary from a few months (with new leaves constantly being grown and old ones shed), to several decades (over thirty years in Great Basin Bristlecone Pine"Pinus longaeva" [Ewers, F. W. & Schmid, R. (1981). Longevity of needle fascicles of "Pinus longaeva" (Bristlecone Pine) and other North American pines. " Oecologia" 51: 107–115.] ).
One additional special case exists in "
Welwitschia", an African gymnospermplant which produces only two leaves, which grow continuously throughout the plant's life but gradually wear away at the apex, giving about 20–40 years' persistence of leaftissue.
There are many different types of evergreens, both trees and shrubs, including most species of: conifers (e.g. white/scots/
jack pine, red cedar, blue spruce), holly, hemlock, 'ancient' gymnosperms like cycads, rainforesttrees and Eucalypts.
Reasons for being evergreen or deciduous
Deciduous trees shed their leaves usually as an adaptation to a cold season or a dry season. Most
tropical rainforestplants are evergreens, replacing their leaves gradually throughout the year as the leaves age and fall, whereas species growing in seasonally arid climates may be either evergreen or deciduous. Most warm temperate climateplants are also evergreen. In cool temperate climates, fewer plants are evergreen, with a predominance of conifers, as few evergreen broadleaf plants can tolerate severe cold below about -30 °C.
In areas where there is a reason for being deciduous (e.g. a cold season or dry season), being evergreen is usually an adaptation to low nutrient levels. Deciduous trees lose nutrients whenever they lose their leaves, and they must replenish these nutrients from the soil to build new leaves. When few nutrients are available, evergreen plants have an advantage. In warmer areas, species such as some
pines and cypresses grow on poor soils and disturbed ground. In " Rhododendron", a genus with many broadleaf evergreens, several species grow in mature forests but are usually found on highly acidic soil where the nutrients are less available to plants. In taigaor borealforests, it is too cold for the organic matter in the soil to decay rapidly, so the nutrients in the soil are less easily available to plants, thus favouring evergreens.
In temperate climates, evergreens can reinforce their own survival; evergreen leaf and needle litter has a higher carbon-nitrogen ratio than deciduous leaf litter, contributing to a higher soil acidity and lower soil nitrogen content. These conditions favour the growth of more evergreens and make it more difficult for deciduous plants to persist. In addition, the shelter provided by existing evergreen plants can make it easier for other evergreen plants to survive cold and/or drought. [Aerts, R. (1995). The advantages of being evergreen. "Trends in Ecology & Evolution" 10 (10): 402–407.] [Matyssek, R. (1986) Carbon, water and nitrogen relations in evergreen and deciduous conifers. "Tree Physiology" 2: 177–187.] [Sobrado, M. A. (1991) Cost-Benefit Relationships in Deciduous and Evergreen Leaves of Tropical Dry Forest Species. "Functional Ecology" 5 (5): 608–616.]
Owing to the botanical meaning, the idiomatic term "evergreen" refers to something that perpetually renews itself, or otherwise remains steady and constant (doesn't suddenly halt or "die off", as leaves on a deciduous tree). An "evergreen market", for example, is one where there is a constant, renewed demand for an item or items, as opposed to a market which is expected to saturate eventually.
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Evergreen — Evergreen, MT U.S. Census Designated Place in Montana Population (2000): 6215 Housing Units (2000): 2532 Land area (2000): 8.012444 sq. miles (20.752134 sq. km) Water area (2000): 0.042377 sq. miles (0.109755 sq. km) Total area (2000): 8.054821… … StarDict's U.S. Gazetteer Places
Evergreen — Saltar a navegación, búsqueda Evergreen Desarrollador Georgia Public Library Service www.open ils.org Información general … Wikipedia Español
Evergreen — Sm langlebiges Musikstück u.ä. erw. fremd. Erkennbar fremd (20. Jh.) Entlehnung. Entlehnt aus ne. evergreen, eigentlich Immergrün , einer Zusammensetzung aus ne. ever immer und ne. green grün . Ebenso nndl. evergreen, ne. evergreen, nschw.… … Etymologisches Wörterbuch der deutschen sprache
Evergreen — (Рим,Италия) Категория отеля: Адрес: Via Milazzo 23 (Check in at Via Marsala 64), Вокзал … Каталог отелей
Evergreen — Ev er*green, n. 1. (Bot.) An evergreen plant. [1913 Webster] 2. pl. Twigs and branches of evergreen plants used for decoration. The funeral evengreens entwine. Keble … The Collaborative International Dictionary of English
Evergreen, AL — U.S. city in Alabama Population (2000): 3630 Housing Units (2000): 1860 Land area (2000): 15.193755 sq. miles (39.351642 sq. km) Water area (2000): 0.060744 sq. miles (0.157326 sq. km) Total area (2000): 15.254499 sq. miles (39.508968 sq. km)… … StarDict's U.S. Gazetteer Places
Evergreen, CO — U.S. Census Designated Place in Colorado Population (2000): 9216 Housing Units (2000): 3840 Land area (2000): 11.582230 sq. miles (29.997837 sq. km) Water area (2000): 0.061964 sq. miles (0.160487 sq. km) Total area (2000): 11.644194 sq. miles… … StarDict's U.S. Gazetteer Places
Evergreen, LA — U.S. town in Louisiana Population (2000): 314 Housing Units (2000): 152 Land area (2000): 1.018993 sq. miles (2.639179 sq. km) Water area (2000): 0.000000 sq. miles (0.000000 sq. km) Total area (2000): 1.018993 sq. miles (2.639179 sq. km) FIPS… … StarDict's U.S. Gazetteer Places
Evergreen, MT — U.S. Census Designated Place in Montana Population (2000): 6215 Housing Units (2000): 2532 Land area (2000): 8.012444 sq. miles (20.752134 sq. km) Water area (2000): 0.042377 sq. miles (0.109755 sq. km) Total area (2000): 8.054821 sq. miles… … StarDict's U.S. Gazetteer Places
Evergreen, WI — U.S. Census Designated Place in Wisconsin Population (2000): 3611 Housing Units (2000): 1267 Land area (2000): 3.814957 sq. miles (9.880694 sq. km) Water area (2000): 0.000000 sq. miles (0.000000 sq. km) Total area (2000): 3.814957 sq. miles… … StarDict's U.S. Gazetteer Places
evergreen — [ev′ər grēn΄] adj. 1. having leaves that are green all year: opposed to DECIDUOUS 2. that remains fresh, vital, interesting, applicable, etc.; timeless n. 1. an evergreen plant or tree, including most conifers and many broad leaved plants, as… … English World dictionary