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Laurel forest, also called laurisilva or laurissilva, is a type of Subtropics forest found in areas with high humidity and relatively stable, mild temperatures. The forest is characterized by broadleaf tree species with evergreen, glossy and leaves, known as "laurophyll" or "lauroid". Plants from the laurel family (Lauraceae) may or may not be present, depending on the location.
These conditions of temperature and moisture occur in four different Geography regions:
Some laurel forests are a type of cloud forest. Cloud forests are found on mountain slopes where the dense moisture from the sea or ocean is precipitated as warm moist air masses blowing off the ocean are forced upwards by the terrain, which cools the air mass to the dew point. The moisture in the air condenses as rain or fog, creating a habitat characterized by cool, moist conditions in the air and soil. The resulting climate is wet and mild, with the annual oscillation of the temperature moderated by the proximity of the ocean.
Some species belong to the true laurel family, Lauraceae, but many have similar foliage to the Lauraceae due to convergent evolution. As in any other rainforest, plants of the laurel forests must adapt to high rainfall and humidity. The trees have adapted in response to these ecological drivers by developing analogous structures, leaves that repel water. Laurophyll or lauroid leaves are characterized by a generous layer of wax, making them glossy in appearance, and a narrow, pointed oval shape with an apical mucro or "drip tip", which permits the leaves to shed water despite the humidity, allowing respiration. The scientific names laurina, laurifolia, laurophylla, lauriformis, and lauroides are often used to name species of other plant families that resemble the Lauraceae.Otto E. (Otto Emery) Jennings. "Fossil plants from the beds of volcanic ash near Missoula, western Montana" Memoirs of the Carnegie Museum, 8(2), p. 417 . The term Lucidophyll, referring to the shiny surface of the leaves, was proposed in 1969 by Tatuo Kira. The scientific names Daphnidium, Daphniphyllum, Daphnopsis, Daphnandra, Daphne Sunset Western Garden Book, 1995:606–607 from Greek: Δάφνη, meaning "laurel", laurus, Laureliopsis, Skimmia laureola, Malosma, laurifolius, Viburnum tinus, Hakea laurina, Prunus laurocerasus (cherry laurel), Prunus lusitanica (Portugal laurel), Corynocarpus laevigatus (New Zealand Laurel), and Corynocarpus rupestris designate species of other plant families whose leaves resemble Lauraceae. The term "lauroid" is also applied to climbing plants such as ivy, whose waxy leaves somewhat resemble those of the Lauraceae.
Mature laurel forests typically have a dense tree canopy and low light levels at the forest floor. Some forests are characterized by an overstory of emergent trees.
Laurel forests are typically multi-species, and diverse in both the number of species and the genera and families represented. In the absence of strong environmental selective pressure, the number of species sharing the arboreal stratum is high, although not reaching the diversity of tropical forests; nearly 100 tree species have been described in the laurisilva rainforest of Misiones (Argentina), about 20 in the Canary Islands. This species diversity contrasts with other temperate forest types, which typically have a canopy dominated by one or a few species. Species diversity generally increases towards the tropics. In this sense, the laurel forest is a transitional type between temperate forests and tropical rainforests.
This type of vegetation characterized parts of the ancient supercontinent of Gondwana and once covered much of the tropics. Some lauroid species that are found outside laurel forests are relicts of vegetation that covered much of the mainland of Australia, Europe, South America, Antarctica, Africa, and North America when their climate was warmer and more humid. Cloud forests are believed to have retreated and advanced during successive geological eras, and their species adapted to warm and wet conditions were replaced by more cold-tolerant or drought-tolerant sclerophyll plant communities. Many of the late Cretaceous – early Tertiary Gondwanan species of flora became extinct, but some survived as relict species in the milder, moister climate of coastal areas and on islands. Thus Tasmania and New Caledonia share related species extinct on the Australian mainland, and the same case occurs on the Macaronesia islands of the Atlantic and on the Taiwan, Hainan, Jeju Island, Shikoku, Kyūshū, and Ryūkyū Islands of the Pacific.
Although some remnants of archaic flora, including species and genera extinct in the rest of the world, have persisted as endemic to such coastal mountain and shelter sites, their biodiversity was reduced. Isolation in these fragmented habitats, particularly on islands, has led to the development of vicariant species and genera. Thus, fossils dating from before the Pleistocene show that species of Laurus were formerly distributed more widely around the Mediterranean and North Africa. Isolation gave rise to Laurus azorica in the Azores Islands, Laurus nobilis on the mainland, and Laurus novocanariensis in the Madeira and the Canary Islands.
Associations of Lauraceous species are common in broadleaved forests; for example, Litsea spp., Persea odoratissima, Persea duthiei, etc., along with such others as Engelhardia spicata, tree rhododendron ( Rhododendron arboreum), Lyonia ovalifolia, wild Himalayan pear ( Pyrus pashia), sumac ( Rhus spp.), Himalayan maple ( Acer oblongum), box myrtle ( Myrica esculenta), Magnolia spp., and birch ( Betula spp.). Some other common trees and large shrub species of subtropical forests are Semecarpus anacardium, Crateva unilocularis, Trewia nudiflora, Premna interrupta, Vietnam elm ( Ulmus lancifolia), Ulmus chumlia, Glochidion velutinum, beautyberry ( Callicarpa arborea), Indian mahogany ( Toona ciliata), fig tree ( Ficus spp.), Mahosama similicifolia, Trevesia palmata, brushholly ( Xylosma longifolium), false nettle ( Boehmeria rugulosa), Heptapleurum venulosum, Casearia graveilens, Actinodaphne reticulata, Sapium insigne, Nepalese alder ( Alnus nepalensis), marlberry ( Ardisia thyrsiflora), holly ( Ilex spp), Macaranga pustulata, Trichilia cannoroides, hackberry ( Celtis tetrandra), Wenlendia puberula, Saurauia nepalensis, ring-cupped oak ( Quercus glauca), Ziziphus incurva, Camellia kissi, Hymenodictyon flaccidum, Maytenus thomsonii, winged prickly ash ( Zanthoxylum armatum), Eurya acuminata, matipo ( Myrsine semiserrata), Sloanea tomentosa, Hydrangea aspera, Symplocos spp., and Cleyera spp.
In the temperate zone, the cloud forest between 2,000 and 3,000 m altitude supports broadleaved evergreen forest dominated by plants such as Quercus lamellosa and Q. semecarpifolia in pure or mixed stands. Lindera and Litsea species, Himalayan hemlock ( Tsuga dumosa), and Rhododendron spp. are also present in the upper levels of this zone. Other important species are Magnolia campbellii, Michelia doltsopa, andromeda ( Pieris ovalifolia), Daphniphyllum himalense, Acer campbellii, Acer pectinatum, and Sorbus cuspidata, but these species do not extend toward the west beyond central Nepal. Nepalese alder ( Alnus nepalensis), a pioneer tree species, grows gregariously and forms pure patches of forests on newly exposed slopes, in gullies, beside rivers, and in other moist places.
The common forest types of this zone include Rhododendron arboreum, Rhododendron barbatum, Lyonia spp., Pieris formosa; Tsuga dumosa forest with such deciduous taxa as maple ( Acer) and Magnolia; deciduous mixed broadleaved forest of Acer campbellii, Acer pectinatum, Sorbus cuspidata, and Magnolia campbellii; mixed broadleaved forest of Rhododendron arboreum, Acer campbellii, Symplocos ramosissima and Lauraceae.
This zone is habitat for many other important tree and large shrub species such as pindrow fir ( Abies pindrow), East Himalayan fir ( Abies spectabilis), Acer campbellii, Acer pectinatum, Himalayan birch ( Betula utilis), Betula alnoides, boxwood ( Buxus rugulosa), Himalayan flowering dogwood ( Cornus capitata), hazel ( Hazel), Deutzia staminea, spindle ( Euonymus tingens), Siberian ginseng ( Acanthopanax cissifolius), Coriaria terminalis ash ( Fraxinus macrantha), Dodecadenia grandiflora, Eurya cerasifolia, Hydrangea heteromala, Ilex dipyrena, privet ( privet spp.), Litsea elongata, common walnut ( Juglans regia), Lichelia doltsopa, Myrsine capitallata, Neolitsea umbrosa, mock-orange ( Philadelphus tomentosus), sweet olive ( Osmanthus fragrans), Himalayan bird cherry ( Prunus cornuta), and Viburnum continifolium.
In ancient times, laurel forests ( shoyojurin) were the predominant vegetation type in the Taiheiyo evergreen forests ecoregion of Japan, which encompasses the mild temperate climate region of southeastern Japan's Pacific coast. There were three main types of evergreen broadleaf forests, in which Castanopsis, Machilus, or Quercus predominated. Most of these forests were logged or cleared for cultivation and replanted with faster-growing , like pine or hinoki, and only a few pockets remain.Karan, Pradyumna Prasad (2005). Japan in the 21st century: environment, economy, and society. University Press of Kentucky, Lexington.. p. 25.
, including orchids, ferns, moss, lichen, and liverworts, are more abundant than in either temperate laurel forests or the adjacent lowland tropical rain forests. Myrtaceae are common at lower elevations, and conifers and rhododendrons at higher elevations. These forests are distinct in species composition from the lowland tropical forests, which are dominated by and other tropical species.
Around 50 million years ago, during the Paleocene, Europe took the form of a set of large islands spread through what was the Tethys Ocean. The climate was wet and Tropical climate with monsoon summer rains. Trees of the laurel and Fagaceae family (Quercus with lauroid-shape leaves and Castanopsis) were common along several species of ferns. Around the Eocene, the planet began cooling, ultimately leading to the Pleistocene glaciations. This progressively deteriorated the Paleotropical flora of Europe, which went extinct in the late Pliocene. Some of these species went globally extinct (e.g. laurophyll Quercus), others survived in the Atlantic islands (e.g. Ocotea), or in other continents (e.g. Magnolia, Liquidambar) and some adapted to the cooler and drier climate of Europe and persisted as relicts in places with high mean annual precipitation or in particular river basins, such as sweet bay (Laurus nobilis) and European holly (Ilex aquifolium), which are fairly widespread around the Mediterranean basin.
Descendants of these species can be found today in Europe, throughout the Mediterranean, especially in the Iberian Peninsula and the southern Black Sea. The most important is Hedera, a climber or vine that is well represented in most of Europe, where it spread again after the glaciations. The portuguese laurel cherry ( Prunus lusitanica) is the only tree that survives as a relict in some Iberian riversides, especially in the western part of the peninsula. In other cases, the presence of Mediterranean laurel ( Laurus nobilis) provides an indication of the previous existence of laurel forest. This species survives natively in Morocco, Algeria, Tunisia, Spain, Portugal, Italy, Greece, the Balkans, and the Mediterranean islands. The Myrtaceae spread through North Africa. Tree heath (Erica arborea) grows in southern Europe, but without reaching the dimensions observed in the temperate evergreen forest of Macaronesia or North Africa. The broad-leaved Rhododendron ponticum baeticum and/or Rhamnus frangula baetica still persist in humid microclimates, such as stream valleys, in the provinces of Cádiz and Málaga in Spain, in the Portuguese Serra de Monchique, and the Rif Mountains of Morocco. The Parque Natural de Los Alcornocales has the biggest and best preserved relicts of Laurisilva in Western Europe.
Although the Atlantic laurisilva is more abundant in the Macaronesian archipelagos, where the weather has fluctuated little since the Tertiary period, there are small representations and some species contribution to the oceanic and Mediterranean ecoregions of Europe, Asia minor and west and north of Africa, where microclimates in the coastal mountain ranges form inland "islands" favorable to the persistence of laurel forests. In some cases these were genuine islands in the Tertiary, and in some cases simply areas that remained ice-free. When the Strait of Gibraltar reclosed, the species repopulated toward the Iberian Peninsula to the north and were distributed along with other African species, but the seasonally drier and colder climate, prevented them reaching their previous extent. In Atlantic Europe, subtropical vegetation is interspersed with taxa from Europe and North Africa in bioclimatic enclaves such as the Serra de Monchique, Sintra, and the coastal mountains from Cadiz to Algeciras. In the Mediterranean region, remnant laurel forest is present on some islands of the Aegean Sea, on the Black Sea coast of Georgia and Turkey, and the Caspian Sea coast of Azerbaijan and Iran, including the Castanopsis and true laurus forests, associated with Prunus laurocerasus, and conifers such as Taxus baccata, Cedrus atlantica, and Abies pinsapo.
In Europe the laurel forest has been badly damaged by timber harvesting, by fire (both accidental and deliberate to open fields for crops), by the introduction of exotic animal and plant species that have displaced the original cover, and by replacement with arable fields, exotic timber plantations, cattle pastures, and and tourist facilities. Most of the biota is in serious danger of extinction. The laurel forest flora is usually strong and vigorous and the forest regenerates easily; its decline is due to external forces.
In Subsaharan Africa, laurel forests are found in the Cameroon Highlands forests along the border of Nigeria and Cameroon, along the East African Highlands, a long chain of mountains extending from the Ethiopian Highlands around the African Great Lakes to South Africa, in the Highlands of Madagascar, and in the montane zone of the São Tomé, Príncipe, and Annobón forests. These scattered highland laurophyll forests of Africa are similar to one another in species composition (known as the Afromontane flora), and distinct from the flora of the surrounding lowlands.
The main species of the Afromontane forests include the broadleaf canopy trees of genus Beilschmiedia, with Apodytes dimidiata, Ilex mitis, Nuxia congesta, Nuxia floribunda, Kiggelaria africana, Prunus africana, Rapanea melanophloeos, Halleria lucida, Ocotea bullata, and Xymalos monospora, along with the emergent conifers Podocarpus latifolius and Afrocarpus falcatus. Species composition of the Subsaharan laurel forests differs from that of Eurasia. Trees of the lauraceae are less prominent, limited to Ocotea or Beilschmiedia due to exceptional Biology and Paleoecology interest and the enormous biodiversity mostly but with many endemic species, and the members of the beech family (Fagaceae) are absent.
Trees can be up to tall and distinct strata of emergent trees, canopy trees, and shrub and herb layers are present. Tree species include: Real Yellowwood ( Podocarpus latifolius), Outeniqua Yellowwood ( Podocarpus falcatus), White Witchhazel ( Trichocladus ellipticus), Rhus chirendensis, Curtisia dentata, Calodendrum capense, Apodytes dimidiata, Halleria lucida, Ilex mitis, Kiggelaria africana, Nuxia floribunda, Xymalos monospora, and Ocotea bullata. Shrubs and climbers are common and include: Common Spikethorn ( Maytenus heterophylla), Cat-thorn ( Scutia myrtina), Numnum ( Carissa bispinosa), Secamone alpinii, Canthium ciliatum, Rhoicissus tridentata, Zanthoxylum capense, and Burchellia bubalina. In the undergrowth grasses, herbs and ferns may be locally common: Basketgrass ( Oplismenus hirtellus), Bushman Grass ( Stipa dregeana var. elongata), Pigs-ears ( Centella asiatica), Cyperus albostriatus, Polypodium polypodioides, Polystichum tuctuosum, Streptocarpus rexii, and Plectranthus spp. Ferns, shrubs and small trees such as Cape Beech ( Rapanea melanophloeos) are often abundant along the forest edges.
Despite being located in a humid climate zone, much of the broadleaf Laurel forests in the Southeast USA are semi-sclerophyll in character. The semi-sclerophyll character is due (in part) to the sandy soils and often periodic semi-arid nature of the climate. As one moves south into central Florida, as well as far southern Texas and the Gulf Coastal margin of the southern United States, the sclerophyll character slowly declines and more tree species from the tropics (specifically, the Caribbean and Mesoamerica) increase as the temperate species decline. As such, the southeastern laurel forests gives way to a mixed landscape of tropical savanna and tropical rainforest.
There are several different broadleaved evergreen canopy trees in the laurel forests of the southeastern United States. In some areas, the evergreen forests are dominated by species of Live oak ( Quercus virginiana), Laurel oak ( Quercus hemisphaerica), southern magnolia ( Magnolia grandiflora), red bay ( Persea borbonia), cabbage palm ( Sabal palmetto), and sweetbay magnolia ( Magnolia virginiana). In several areas on the barrier islands, a stunted Quercus geminata or mixed Q. geminata and Quercus virginiana forest dominates, with a dense evergreen understory of scrub palm Serenoa repens and a variety of vines, including Bignonia capreolata, as well as Smilax and Vitis species'. Gordonia lasianthus, Ilex opaca and Osmanthus americanus also may occur as canopy co-dominant in coastal dune forests, with Cliftonia monophylla and Vaccinium arboreum as a dense evergreen understory (Box and Fujiwara 1988).
The lower shrub layer of the evergreen forests is often mixed with other evergreen species from the palm family ( Rhapidophyllum hystrix), bush palmetto ( Sabal minor), and saw palmetto ( Serenoa repens), and several species in the Ilex family, including Ilex glabra, Dahoon holly, and Yaupon holly. In many areas, Cyrilla racemiflora, Lyonia fruticosa, wax myrtle Myrica is present as an evergreen understory. Several species of Yucca and Opuntia are native as well to the drier sandy coastal scrub environment of the region, including Yucca aloifolia, Yucca filamentosa, Yucca gloriosa, and Opuntia stricta.
There are however, several areas in Mediterranean California, as well as isolated areas of southern Oregon that have evergreen forests. Several species of evergreen Quercus forests occur, as well as a mix of evergreen scrub typical of Mediterranean climates. Species of Notholithocarpus, Arbutus menziesii, and Umbellularia californica can be canopy species in several areas.
Beilschmiedia tawa is often the dominant canopy species of the laural genus Beilschmiedia in lowland laurel forests in the North Island and the northeast of the South Island, but will also often form the subcanopy in primary forests throughout the country in these areas, with Podocarpaceae. Genus Beilschmiedia are trees and widespread in tropical Asia, Africa, Australia, New Zealand, Central America, the Caribbean, and South America as far south as Chile. In the Corynocarpus family, Corynocarpus laevigatus is sometimes called laurel of New Zealand, while Laurelia novae-zelandiae belongs to the same genus as Laurelia sempervirens. The tree niaouli grows in Australia, New Caledonia, and Papua.
The New Guinea and Northern Australian ecoregions are also closely related.
The highlands of New Guinea and New Britain are home to montane laurel forests, from about elevation. These forests include species typical of both Northern Hemisphere laurel forests, including Lithocarpus, Ilex, and Lauraceae, and Southern Hemisphere laurel forests, including Southern Beech Nothofagus, Araucaria, , and trees of the Myrtle family (Myrtaceae). New Guinea and Northern Australia are closely related. Around 40 million years ago, the Indo-Australian tectonic plate began to split apart from the ancient supercontinent Gondwana. As it collided with the Pacific Plate on its northward journey, the high mountain ranges of central New Guinea emerged around 5 million years ago.Frith, D.W., Frith, C.B. (1995). Cape York Peninsula: A Natural History. Chatswood: Reed Books Australia. Reprinted with amendments in 2006. . In the lee of this collision zone, the ancient rock formations of what is now Cape York Peninsula remained largely undisturbed.
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