Evergreen – New World Encyclopedia

A silver fir shoot displaying three successive years of retained leaves.

In botany, the time period evergreen refers to a tree, shrub, or different plant having foliage that persists all year long. This terminology consists of temperate and Arctic-zone cold-tolerant species whose foliage stays all through the winter and into the subsequent rising season the next summer time, and tropical and semi-tropical vegetation whose foliage stays for multiple annual cycle. Evergreen contrasts with deciduous, which refers to vegetation that fully lose their foliage for a part of the 12 months.

Leaf persistence in evergreen vegetation might differ from a couple of months (following a continuing course of of recent leaves being grown and outdated ones shed) to a number of many years (over thirty years in Nice Basin bristlecone pine Pinus longaeva) (Ewers and Schmid 1981).

There are lots of several types of evergreens, together with timber, shrubs, and vines; species of conifers, flowering vegetation, and cycads; and vegetation with broadleaf, needlelike, scalelike, or different leaf sorts. Evergreens embrace most species of conifers (for instance, white/scots/jack pine, pink cedar, blue spruce), in addition to such vegetation as holly, palms, gymnosperms like cycads, rainforest timber, and eucalypts. Retention of leaves even through the winter confers sure benefits to evergreen timber, however for people in chilly climates it additionally provides to the variety and fantastic thing about nature, offering inexperienced foliage in stark distinction to the snow and leafless timber.

Owing to the botanical which means, the idiomatic time period “evergreen” has come to confer with one thing that perpetually renews itself, or in any other case stays regular and fixed (doesn’t all of a sudden halt or “die off,” as leaves on a deciduous tree.) In enterprise, for instance, an evergreen market is one the place there’s a fixed, renewed demand for an merchandise or objects. In folks customs, a excessive proportion of vegetation utilized are evergreen, both due to symbolic meanings—comparable to representing the unconquered life-force or immortality—or due to the practicality of being out there in all seasons (Simpson and Roud 2000).

Overview

A Southern reside oak in winter

The 2 fundamental classes of vegetation delineated by way of period of leaves are deciduous and evergreen.

In botany and horticulture, deciduous vegetation, together with timber, shrubs and herbaceous perennials, are those who lose all of their leaves for a part of the 12 months. This strategy of leaf loss is known as abscission. In some instances, leaf loss coincides with winter—specifically in temperate or polar climates. In different areas of the world, together with tropical, subtropical and arid areas, vegetation might lose their leaves through the dry season or throughout different seasonal differences in rainfall. The deciduous attribute happens extensively amongst woody vegetation. Deciduous timber embrace maple, many oaks, elm, aspen, and birch, amongst others, in addition to various coniferous genera, comparable to larch and Metasequoia. Deciduous shrubs embrace honeysuckle, poison oak, and plenty of others. Most temperate woody vines are additionally deciduous, together with grapes, poison ivy, virginia creeper, wisteria, and so forth. Nonetheless, there aren’t any deciduous species amongst tree-like monocotyledonous vegetation, comparable to palms and yucca.

The converse of deciduous is evergreen, wherein inexperienced foliage is persistent 12 months spherical. Within the Glossary of Botanical Phrases used within the OpenKey Challenge of College of North Carolina at Chapel Hill and the College of Illinois at Urbana-Champaign, evergreen is outlined as “bearing inexperienced leaves by means of the winter and into the subsequent rising season” and “persisting two or extra rising seasons” (Seiberling 2005). Though the time period evergreen usually is used as if synonymous with the cone-bearing conifers (division Pinophyta), significantly these with needle-like leaves, evergreen consists of all varieties of vegetation, with many broad-leafed flowering vegetation having foliage that persists all year long in tropical and semi-tropical areas, whereas some conifers, such because the larch (genus Larix) with its needle-like leaves, are usually not evergreen, however deciduous.

The persistence of leaves in evergreen vegetation varies from a couple of months, with new leaves continuously changing outdated ones which might be shed, to leaves lasting over thirty years within the Nice Basin bristlecone pine, Pinus longaeva (Ewers and Schmid 1981). Nonetheless, only a few species present leaf persistence of greater than 5 years. A further particular case exists in Welwitschia, an African gymnosperm plant that produces solely two leaves, which develop repeatedly all through the plant’s life however regularly put on away on the apex, giving about 20–40 years’ persistence of leaf tissue.

There are also botanical classes intermediate between deciduous and evergreen. Semi-deciduous vegetation lose their outdated foliage as new development begins; that’s, they lose their foliage for a really brief interval, when outdated leaves fall off and new foliage development is beginning. This phenomenon happens in tropical and sub-tropical woody species, for instance in Mimosa bimucronata. Semi-deciduous may additionally describe mild-weather timber that lose leaves in a fashion just like deciduous timber in an particularly chilly autumn. Semi-evergreen may additionally describe vegetation that lose their leaves earlier than the subsequent rising season however retain some throughout winter or throughout dry durations (Weber 2001). Seiberling (2005) defines semi-evergreen (additionally tardily deciduous or winter deciduous) as “bearing inexperienced leaves into or by means of the winter, however dropping them by the start of the subsequent rising season.” Some timber, together with a couple of oak species, retain desiccated leaves on the tree by means of winter; these dry persistent leaves are referred to as marcescent leaves and are dropped within the spring as new development begins.

The attribute of evergreen versus deciduous is helpful in plant identification. As an example, in components of Southern California and the American Southeast, deciduous and evergreen oak species might develop facet by facet.

Causes for being evergreen or deciduous

Deciduous timber shed their leaves often as an adaptation to a chilly season or a dry season. Most tropical rainforest vegetation are evergreens, changing their leaves regularly all year long because the leaves age and fall, whereas species rising in seasonally arid climates could also be both evergreen or deciduous. Most heat temperate local weather vegetation are additionally evergreen. In cool temperate climates, fewer vegetation are evergreen, with a predominance of needle-leaf conifers, as few evergreen broadleaf vegetation can tolerate extreme chilly under about -30 °C (-22 °F).

In areas the place there’s a motive for being deciduous (for instance, a chilly season or dry season), being evergreen is often an adaptation to low nutrient ranges. Deciduous timber lose vitamins every time they lose their leaves, they usually should replenish these vitamins from the soil to construct new leaves. When few vitamins can be found, evergreen vegetation have a bonus. In hotter areas, species comparable to some pines and cypresses develop on poor soils and disturbed floor. In Rhododendron, a genus with many broadleaf evergreens, a number of species develop in mature forests however are often discovered on extremely acidic soil the place the vitamins are much less out there to vegetation. In taiga or boreal forests, it’s too chilly for the natural matter within the soil to decay quickly, so the vitamins within the soil are much less simply out there to vegetation, thus favoring evergreens.

In temperate climates, evergreens can reinforce their very own survival; evergreen leaf and needle litter has a better carbon-nitrogen ratio than deciduous leaf litter, contributing to a better soil acidity and decrease soil nitrogen content material. These situations favor the expansion of extra evergreens and make it tougher for deciduous vegetation to persist. As well as, the shelter supplied by present evergreen vegetation could make it simpler for different evergreen vegetation to outlive chilly and/or drought (Aerts 1995; Matyssek 1986; Sobrado 1991).

Crops with deciduous foliage have each benefits and downsides in comparison with vegetation with evergreen foliage. Since deciduous vegetation lose their leaves to preserve water or to raised survive winter climate situations, they have to regrow new foliage through the subsequent appropriate rising season; this makes use of extra assets, which evergreens don’t have to expend. Evergreens as compared endure better water loss through the winter they usually can also expertise better predation stress, particularly when small. Shedding leaves in winter might cut back injury from bugs; repairing leaves and preserving them useful could also be extra expensive than simply shedding and regrowing them (Labandeira et al. 1994).

References

  • Aerts, R. 1995. The benefits of being evergreen. Tendencies in Ecology & Evolution 10(10): 402–407.
  • Ewers, F. W., and R. Schmid. 1981. Longevity of needle fascicles of Pinus longaeva (Bristlecone pine) and different North American pines. Oecologia 51: 107–115..
  • Labandeira, C. C., D. L. Dilcher, D.R. Davis, and D. L. Wagner. 1994. Ninety-seven million years of angiosperm-insect affiliation: Paleobiological insights into the which means of coevolution Proceedings of the Nationwide Academy of Sciences of the USA of America 91(25): 12278-12282. Retrieved Might 23, 2008.
  • Matyssek, R. 1986. Carbon, water and nitrogen relations in evergreen and deciduous conifers. Tree Physiology 2: 177–187.
  • Seiberling, S. M. 2005. Glossary of botanical phrases used within the OpenKey Challenge. The Illinois-North Carolina Collaborative Surroundings for Botanical Assets. Retrieved Might 23, 2008.
  • Simpson, J., and S. Roud. 2000. A Dictionary of English folklore. Oxford: Oxford Univ. Press. ISBN 058548628X.
  • Sobrado, M. A. 1991. Price-benefit relationships in deciduous and evergreen leaves of tropical dry forest species. Purposeful Ecology 5(5): 608–616.
  • Weber, W. 2001. African Rain Forest Ecology and Conservation: An Interdisciplinary Perspective. New Haven: Yale College Press. ISBN 0300084331.

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