Laurasilva

Laurel forest, also called laurisilva or laurissilva, is a type of subtropical forest found in areas with high humidity and relatively stable, mild temperatures. The forest is characterized by broadleaf tree species with evergreen, glossy and elongated leaves, known as "laurophyll" or "lauroid". Plants from the laurel family (Lauraceae) may or may not be present, depending on the location.

Ecology

Laurel and laurophyll forests have a patchy distribution in warm temperate regions, often occupying topographic refugia where the moisture from the ocean condenses so that it falls as rain or fog and soils have high moisture levels.Abstract
at NASA – MODIS: Izquierdo, T; de las Heras, P; Marquez, A (2011). Vegetation indices changes in the cloud forest of La Gomera Island (Canary Islands) and their hydrological implications". ''Hydrological Processes'', 25(10), 1531–41: " sults prove the absence of summer drought stress in the laurel forest implying that the fog drip income is high enough to maintain enough soil moisture". They have a mild climate, seldom exposed to fires or frosts and are found in relatively acidic soils. Primary productivity is high, but can be limited by mild summer drought. The canopies are evergreen, dominated by species with glossy- or leathery-leaves, and with moderate tree diversity. Insects are the most important herbivores, but birds and bats are the predominant seed-dispersers and pollinators. Decomposers such as invertebrates, fungi, and microbes on the forest floor are critical to nutrient cycling.

These conditions of temperature and moisture occur in four different geographical regions:
* Along the eastern margin of continents at latitudes of 25° to 35°.
* Along the western coast of continents between 35° and 50° latitude.
* On islands between 25° and 35° or 40° latitude.
* In humid montane regions of the tropics.

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.

Characteristics

Laurel forests are characterized by evergreen and hardwood trees, reaching up to in height. Laurel forest, laurisilva, and laurissilva all refer to plant communities that resemble the bay laurel.

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'' from Greek: Δάφνη, meaning "laurel", ''laurus'', ''Laureliopsis'', '' laureola'', '' laurelin'', '' laurifolia'', '' laurifolius'', '' lauriformis'', '' 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 ivies, 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.

Origin

Laurel forests are composed of vascular plants that evolved millions of years ago. Lauroid floras have included forests of Podocarpaceae and southern beech.

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, 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 glaciations 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.

Ecoregions

Laurel forests occur in small areas where their particular climatic requirements prevail, in both the northern and southern hemispheres. Inner laurel forest ecoregions, a related and distinct community of vascular plants, evolved millions of years ago on the supercontinent of Gondwana, and species of this community are now found in several separate areas of the Southern Hemisphere, including southern South America, southernmost Africa, New Zealand, Australia and New Caledonia. Most Laurel forest species are evergreen, and occur in tropical, subtropical, and mild temperate regions and cloud forests of the northern and southern hemispheres, in particular the Macaronesian islands, southern Japan, Madagascar, New Caledonia, Tasmania, and central Chile, but they are pantropical, and for example in Africa they are endemic to the Congo region, Cameroon, Sudan, Tanzania, and Uganda, in lowland forest and Afromontane areas.
Since laurel forests are archaic populations that diversified as a result of isolation on islands and tropical mountains, their presence is a key to dating climatic history.

East Asia

Laurel forests are common in subtropical eastern Asia, and form the climax vegetation in far southern Japan, Taiwan, southern China, the mountains of Indochina, and the eastern Himalayas. In southern China, laurel forest once extended throughout the Yangtze Valley and Sichuan Basin from the East China Sea to the Tibetan Plateau. The northernmost laurel forests in East Asia occur at 39° N. on the Pacific coast of Japan. Altitudinally, the forests range from sea-level up to 1000 metres in warm-temperate Japan, and up to 3000 metres elevation in the subtropical mountains of Asia. Some forests are dominated by Lauraceae, while in others evergreen laurophyll trees of the beech family (Fagaceae) are predominant, including ring-cupped oaks (''Quercus'' subgenus ''Cyclobalanopsis''), chinquapin (''Castanopsis'') and tanoak (''Lithocarpus''). Other characteristic plants include ''Schima'' and ''Camellia'', which are members of the tea family (Theaceae), as well as magnolias, bamboo, and rhododendrons. These subtropical forests lie between the temperate deciduous and conifer forests to the north and the subtropical/tropical monsoon forests of Indochina and India to the south.

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

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