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Sclerophyll is a type of vegetation that is adapted to long periods of dryness and heat. The plants feature hard leaves, short internodes (the distance between leaves along the stem) and leaf orientation which is parallel or oblique to direct sunlight.
Sclerophyllous plants occur in many parts of the world,C. Michael Hogan. 2010. Leather Oak, Quercus durata. Encyclopedia of Earth. National Council for Science and Environment. Washington, DC but are most typical of areas with low rainfall or seasonal droughts, such as Australia, Africa, and western North and South America. They are prominent throughout Australia, parts of Argentina, the Cerrado biogeographic region of Bolivia, Paraguay and Brazil, and in the Mediterranean biomes that cover the Mediterranean Basin, California, Chilean Matorral, and the Cape Province of South Africa.
In the Mediterranean basin, Quercus ilex, cork oak and are typical hardwood trees. In addition, there are several species of pine under the trees in the vegetation zone. The shrub layer contains numerous herbs such as rosemary, thyme and lavender. In relation to the potential natural vegetation, around 2% of the Earth's land surface is covered by sclerophyll woodlands, and a total of 10% of all plant species on Earth live there.
Plant species with this type of adaptation tend to be evergreen with great longevity, slow growth and with no loss of leaves during the unfavorable season. As a result, the that make up these are of the persistent evergreen type, in addition to the predominance of plants, even herbaceous ones, with "hard" leaves, which are covered by a thick leathery layer called the cuticle, that prevents water loss during the dry season. The aerial and underground structures of these plants are modified to make up for water shortages that may affect their survival.
The name sclerophyll derives from the highly developed sclerenchyma from the plant, which is responsible for the hardness or stiffness of the leaves. This structure of the leaves inhibits transpiration and thus prevents major water losses during the dry season. Most of the plant species in the sclerophyll zone are not only insensitive to summer drought, they have also used various strategies to adapt to frequent wildfires, heavy rainfall and Soil nutrient deficiencies. (1997). 9783800134892, Ulmer. ISBN 9783800134892
Generally, the summers are dry and hot with a dry season of a maximum of seven months, but at least two to three months. The winters are rainy and cool. However, not all regions with sclerophyll vegetation feature the classic Mediterranean climate; parts of eastern Italy, eastern Australia and eastern South Africa, which feature sclerophyll woodlands, tend to have uniform rainfall or even a more summer-dominant rainfall, whereby falling under the humid subtropical climate zone ( Cfa/ Cwa). Furthermore, other areas with sclerophyll flora would grade to the oceanic climate ( Cfb); particularly the eastern parts of the Eastern Cape province in South Africa, and Tasmania, Victoria and southern New South Wales in Australia.
Sclerophylly's advantages in nutrient-poor conditions may be another factor in the prevalence of sclerophyllous plants in nutrient-poor areas in drier-climate regions, like much of Australia and the Cerrado of Brazil.
The sclerophyll zone often merges into temperate deciduous forests towards the poles, on the coasts also into temperate rainforests and towards the equator in hot or deserts. The Mediterranean areas, which have a very high biodiversity, are under great pressure from the population. This is especially true for the Mediterranean region since ancient times. Through overexploitation (logging, grazing, agricultural use) and frequent fires caused by people, the original forest vegetation is converted. In extreme cases, the hard-leaf vegetation disappears completely and is replaced by open rock .
Some sclerophyll areas are closer to the equator than the Mediterranean zone—for example, the interior of Madagascar, the dry half of New Caledonia, the lower edge areas of the Madrean pine-oak woodlands of the Mexican highlands between or around high plateaus of the Asir Mountains on the western edge of the Arabian Peninsula.
In the course of the last millennia, the original vegetation in almost all areas of this vegetation zone has been greatly changed by the influence of humans. Where the plants have not been replaced by and olive groves, the maquis shrubland was the predominant form of vegetation on the Mediterranean. The maquis has been degraded in many places to the low shrub heather, the garrigue. Many plant species that are rich in aromatic oils belong to both vegetation societies. The diversity of the original sclerophyll vegetation in the world is high to extremely high (3,000–5,000 species per hectare).Klaus Müller-Hohenstein: The geo-ecological zones of the Earth. In: Geography and School. Issue 59, Bayreuth 1989.
The most common sclerophyll communities in Australia are dominated by grasses with an overstorey of eucalypts and acacias. Acacia (particularly Acacia aneura) also cover extensive areas. All the dominant overstorey acacia species and a majority of the understorey acacias have a scleromorphic adaptation in which the leaves have been reduced to consisting entirely of the petiole.
Many plants of the sclerophyllous woodlands and shrublands also produce leaves unpalatable to herbivores by the inclusion of toxic and indigestible compounds which assure survival of these long-lived leaves. This trait is particularly noticeable in the eucalypt and Melaleuca species which possess oil glands within their leaves that produce a pungent volatile oil that makes them unpalatable to most browsers. These traits make the majority of woody plants in these woodlands largely unpalatable to domestic livestock.Mott, J. J., and J. C. Tothill. 1984. Tropical and subtropical woodlands. in G. N. Harrington and A. D. Wilson, editors. Management of Australia's Rangelands. CSIRO Publishing, Melbourne It is therefore important from a grazing perspective that these woodlands support a more or less continuous layer of herbaceous ground cover dominated by grasses.
Sclerophyll forests cover a much smaller area of the continent, being restricted to relatively high rainfall locations. They have a eucalyptus overstory (10 to 30 metres) with the understory also being hard-leaved. Dry sclerophyll forests are the most common forest type on the continent, and although it may seem barren dry sclerophyll forest is highly diverse. For example, a study of sclerophyll vegetation in Seal Creek, Victoria, found 138 species.
Even less extensive are wet sclerophyll forests. They have a taller eucalyptus overstory than dry sclerophyll forests, or more (typically mountain ash, alpine ash, rose gum, karri, messmate stringybark, or manna gum, and a soft-leaved, fairly dense understory ( are common). They require ample rainfall—at least 1000 mm (40 inches).
Most of the wooded parts of present-day Australia have become sclerophyll dominated as a result of the extreme age of the continent combined with Aboriginal fire use. Deep weathering of the crust over many millions of years leached chemicals out of the rock, leaving Australian soils deficient in nutrients, particularly phosphorus. Such nutrient deficient soils support non-sclerophyllous plant communities elsewhere in the world and did so over most of Australia prior to European arrival. However such deficient soils cannot support the nutrient losses associated with frequent fires and are rapidly replaced with sclerophyllous species under traditional Aboriginal burning regimens. With the cessation of traditional burning non-sclerophyllous species have re-colonized sclerophyll habitat in many parts of Australia.
The presence of toxic compounds combined with a high carbon : nitrogen ratio make the leaves and branches of scleromorphic species long-lived in the litter, and can lead to a large build-up of litter in woodlands.
All the Australian sclerophyllous communities are liable to be burnt with varying frequencies and many of the woody plants of these woodlands have developed adaptations to survive and minimise the effects of fire.Harrington, G. N., M. H. Friedel, K. C. Hodgkinson, and J. C. Noble. 1984. Vegetation ecology and management. in G. N. Harrington and A. D. Wilson, editors. Management of Australia's Rangelands. CSIRO Publishing, Melbourne.
Sclerophyllous plants generally resist dry conditions well, making them successful in areas of seasonally variable rainfall. In Australia, however, they evolved in response to the low level of phosphorus in the soil—indeed, many native Australian plants cannot tolerate higher levels of phosphorus and will die if fertilised incorrectly. The leaves are hard due to lignin, which prevents wilting and allows plants to grow, even when there is not enough phosphorus for substantial new cell growth.
Distribution
The zone of the sclerophyll vegetation lies in the border area between the subtropics and the temperate zone, approximately between the 30th and 40th degree of latitude (in the northern hemisphere also up to the 45th degree of latitude). Their presence is limited to the coastal western sides of the continents, but nonetheless can typical in any regions of a continent with scarce annual precipitation or frequent seasonal droughts and poor soils that are heavily leached.Susanne Heise: Vegetation zones: The zone of the evergreen hardwood plants, in TERRA-Online/Realschule on Klett.de, Klett, Leipzig 2003, version January 26, 2006, accessed on December 17, 2020.
(1976). 9783411003037, Bibliograph. Inst. ISBN 9783411003037
Land use
While the winter rain areas of America, South Africa and Australia, with an unusually large variety of food , were ideal gathering areas for until European colonization, agriculture and cattle breeding spread in the Mediterranean area since the Neolithic, which permanently changed the face of the landscape. In the sclerophyll regions near the coast, permanent crops such as olive and wine cultivation established themselves; However, the landscape forms that characterize the degenerate shrubbery and shrub heaths Maquis shrubland and garrigue are predominantly a result of grazing (especially with goats).
Australian bush
Most areas of the Australian continent able to support woody plants are occupied by sclerophyll communities as , , or heathlands. Common plants include the Proteaceae (, and ), Melaleuca, , , and .
Evolution
Sclerophyllous plants are all part of a specific environment and are anything but newcomers. By the time of European settlement, sclerophyll forest accounted for the vast bulk of the forested areas.
(1988). 9780730101543, Reed Books. ISBN 9780730101543 The toxic compounds of many species, notably Eucalyptus species, are volatile and flammable and the presence of large amounts of flammable litter, coupled with an herbaceous understorey, encourages fire.
Regions
These are the biomes or ecoregions in the world that feature an abundance of, or are known for having, sclerophyll vegetation:
See also
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