Laurissilva
The laurel forest (from Latin: laurus+silva 'laurel forest'), Also called temperate jungle or laurifolio forest, it is a type of subtropical cloud forest or high jungle, typical of humid, warm places and with slight or no frost, with large trees, vines and lianas whose leaves resemble those of the laurel, from which it takes its name. Laurissilva occurs in regions with a humid and warm temperate climate.
General information
The laurel or temperate evergreen forest (with persistent foliage) represents the characteristic vegetation of a climatic regime with well-defined seasons, but lacking marked contrasts: the annual temperature variation is moderate, without excluding winter frosts and the abundant rainfall is well distributed throughout the year, without a defined dry season.
These conditions occur in three different geographical regions, and for no less disparate reasons:
- along the eastern margin of the continents in the latitudes of 25° to 35°;
- on the continental coasts of west between 40° and 55° latitude, and
- on the islands between 25° and 35° or 40° south latitude.
- has tempered and wet climate
Examples of the first are the lands of southeastern Brazil and the immediate vicinity in Argentina, Paraguay and Uruguay. The second category corresponds, with various nuances, to the coastal territory of Chile and southwestern Argentina from Valdivia to the extreme south of the continent (Valdivian Forest Ecoregion). Finally, the third category includes the Canary Islands, Madeira, Salvajes Islands, Azores and Cape Verde, which together make up the so-called Macaronesian region. Outside these latitudes, they can appear locally in microenvironments with a favorable climate due to other factors such as abundance of water and the isolation of relict communities without competitors. The temperate climate humid forest has given rise to communities of laurel species in numerous temperate climate zones on Earth.
Only a few species of laurel belong to the laurel family, although the appearance of most resemble these plants or the Rutaceae, this is due to evolutionary convergence. As in any other jungle, the laurel plants have to avoid excess humidity, which here becomes a problem. For this they have adopted a common strategy, developing leaves that repel water from their surface. The so-called laurel leaf (or lauroid), in analogy to those of the genus Laurus, thanks to the abundant layer of wax and the apical mucron that favors dripping, remains dry despite the environmental humidity, which allows transpiration and respiration of the plant. Others are added to this strategy, such as lianoid growth and epiphytism, very common among cryptogams. Under the lauroid canopy, various species typical of tropical forests also survive. It is characterized by understory species associated with tree species typical of this type of cloud forest.
In Eurasia and North America, the species, with lauroid-type leaves, are: Perseas, prunus, maytenus, ocoteas, ilex, oaks, rutaceae, laurels, chestnuts, yews, tree heathers, rhododendrons, bamboos, ferns, mosses and liverworts.
In the southern hemisphere they are also joined by a greater number of exclusive conifers, such as certain araucarias; the notophagaceae, which are close relatives of beeches and oaks, tree ferns and epiphytic mosses.
Features
from Gato Water, Santiago Island, Cape Verde. Note the condensation fog that define it as a cloud forest.
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It is a type of rain forest or humid forest, that is to say, a plant ecosystem of great exuberance characterized by high humidity, without seasonal changes and with a great diversity of botanical and zoological species but also of great fragility in the face of aggressions medium. It is characterized by evergreen and hardwood trees, reaching up to 40 meters in height.
Laurisilvas are generally evergreen and multi-specific forests. Evergreen because the mild climate allows continuous biological activity, and multispecific because of the notable diversity of tree species in the forest canopy. Indeed, in the absence of a strong environmental selective pressure, the number of species that share the tree layer is high: almost 100 species of trees have been described in the Argentine missionary forest, some 20 in the Canary Islands, without reaching the values of the tropical forests. It is precisely this multispecificity that deserves the name forest, in contrast to forests: Mediterranean forests, temperate deciduous forests, etc., whose tree canopy is monospecific or dominated by by one or a few species. In this sense, the laurel forest is a transit formation between temperate forests and tropical forests.
However, despite the large number of species, there is a notable morphological convergence between the different tree species, especially in the leaves, which correspond mainly to the "laurel" type: broad, oval, leathery, glossy. Hence the name given to this formation: laurisilva.
Cloud forests develop preferentially around mountains, where the dense moisture from the sea or ocean precipitates due to the action of the relief. The orography of the terrain, opposite to the warm and humid air front, forces the height above sea level of this humid and warm air mass to increase, which cools it and lowers its dew point and causes part of it to condense. its moisture, which precipitates in the form of fog or rain and creates a particularly hydrophilic habitat, saturated with moisture in the environment and in the soil.
The Mediterranean climate is the result of the warm and dry influence of subtropical anticyclones, dry and hot summer, and the current of polar, Antarctic or arctic air, responsible for the rain-bearing storms, cool and humid winter.
As the latitude increases, the influence of the storms is accentuated, which, on their journey from west to east, sweep the western coasts of the continents, discharging the high humidity they carry in the form of copious rainfall; precipitation that multiplies if these air masses find mountains in their path. The resulting climate is wetter and cooler than the Mediterranean, but with an annual temperature fluctuation moderated by the proximity of the ocean.
These are the climatic conditions of Chile between 38º and 45º latitude. Rainfall is abundant, from 1,500 to 5,000 mm depending on the location, and is regularly distributed throughout the year, although the Mediterranean influence is still noticeable with 3-4 sub-humid months in summer. The temperatures are very constant and mild, with no average month falling below 5 °C, and with values below 22 °C for the warmest month.
The coasts of Brazil and Argentina, between 25º and 35º latitude, are under a typical laurel weather regime. This region is still in the area of influence of the subtropical anticyclone, which sends warm, humid and unstable air towards high latitudes on this flank. During the summer the anticyclone strengthens and the flow of humid air increases, which, when rising and cooling, produces heavy precipitation. In winter the anticyclone withdraws and the entry of polar air from the west is reinforced, which causes rain-bearing storms. Overall, the average annual rainfall varies, depending on the localities, between 1,500 and 2,000 mm. The average temperature is around 20-21 °C, with mild winters and not excessively hot summers, due to the moderating effect of the abundant rainfall. This softness does not exclude the possibility of frost and even snowfall in the highest regions, which is a limiting factor for species at lower latitudes. A climate with these characteristics is classified as humid subtropical or rainy temperate with hot summers.
The Atlantic laurel forest covered the European continent, North Africa and the Near East in Asia, during the Tertiary Era, when a tropical climate dominated the Mediterranean basin. Currently, its largest populations are found on the Macaronesian islands (Canary Islands, Madeira), in the North Atlantic Ocean, where they form the so-called laurel or monteverde.
It has deep soils and is typical of the northern midlands influenced by the mists of the trade winds, devoid of frost, with rainfall of 500 to 1100 mm per year and an average annual temperature of between 15 and 19 °C. It includes a great variety of trees, understory plants and species of insects and animals that live in conditions of humidity greater than 80%; It usually appears in areas with abundant rainfall, and occupies the majority of the favorable areas in the north of the islands between 400 and 1,500 meters, and thus benefits from the humidity provided by the trade winds as they form a sea of clouds. It includes two subtypes of forest: laurilsilva and fayal-brezal. Due to the abundant amount of water and the orography, it flows in the form of streams and waterfalls everywhere or remains calm in pools and pools or drips, covers and soaks the plants, rocks, soil, trunks, mosses, etc. and even though the jungle is impassable during heavy rains, the beauty of the complex makes it a tourist attraction.
Notable formations of laurel forests are found both for biodiversity and extent in Southeast Asia and Africa, both continental and on islands, being the typical Annobon formation, but these formations are less studied.
Origin of the laurel forest
Over millions of years, these plant formations covered much of the Earth's tropics. From a biogeographical point of view, the tropics may extend beyond the parallels of Cancer and Capricorn, v. gr., the Florida peninsula in the United States lies in the subtropics (latitude greater than 23º25'N) but is home to many species characteristic of the New World tropics.
An example is the translation of the Atlantic laurel forests from the Tertiary to their current location. Many Macaronesian laurel plants have their closest relatives in places as geographically remote as South Africa or South America, the genera Persea, Ocotea and Maytenus, for example, they also appear in the South American laurisilvas, which testifies to the ancient origin of this flora. Another interesting fact is the presence in various locations in the Mediterranean, the Caucasus and even the Himalayas, of fossil plants from about 20 million years ago, Tertiary, very similar or identical to those that live today in Macaronesia.
The Macaronesian laurel forests are remnants of the vegetation that originally covered the Atlantic to the Caspian Sea before the ice ages. This type of jungle extended during the Cenozoic or Tertiary Era, more than 20 million years ago, over a wide area of the Mediterranean basin, Eurasia and northwest Africa when the region's climate was more humid. At that time, the Tethys Sea existed, separating the ancient continents of Laurasia and Gondwana. This sea was much more open than the Mediterranean and ocean currents flowed differently, bringing humidity and tempering of climatic extremes to areas where they are currently they have no influence. At that time, the climate of southern Europe was warmer and more humid than today, and the vegetation that surrounded the shores of the ancient Mediterranean Sea must have been similar to that of today's Macaronesian laurel forest.
Later, when the glaciations occurred, which took place at the end of said period and during a good part of the Quaternary, and the expansion of the polar caps, with the consequent generalized cooling of the climate, they began to displace the flora of central and southern Europe it withdrew towards more temperate regions of the south, where conditions were more propitious for its survival, settling in this way on the northwestern coast of Africa and in the Macaronesian archipelagos.
At the end of the ice ages, the extension of the deserts began in North Africa, so this type of forest was reduced to those areas that act as borders between the temperate and tropical zones.
With the greater periodic drought of the climate of the Mediterranean basin as a consequence of climatic changes due to changes in ocean currents and continental drifts during the Pliocene, the laurel forests gradually withdrew, replaced by plant communities of more tolerant sclerophyll flora to drought. Most of the last remaining laurel forest around the Mediterranean is believed to have disappeared around 10,000 years ago at the end of the Pleistocene, when the Mediterranean basin became warmer and drier, although some remnants of forest flora of laurel still persist in the southern mountains in Spain, north-central Portugal and north Morocco, and three constituent species: Laurus nobilis, Ilex aquifolium and Hedera helix remain extensive. A notable adaptation is the asparagus: while in the Canary Islands the original form, a leafy vine, is preserved, in the rest of the Mediterranean it has evolved into a thorny species. The location of the Macaronesian islands in the North Atlantic Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate that has allowed these forests to persist to this day.
Almost at the same time, North Africa began to dry out, giving rise to the present Sahara desert.
Many of the existing species then became extinct because they could not overcome the barriers posed by the Alpine mountains and the Mediterranean, but others found refuge as relict species in coastal enclaves and in the Macaronesian archipelagos, far enough from the ice and at the same time protected by the oceanic influence of the drying up that originated the Sahara. In other parts of the world, such as China, Africa or South America, the arrangement of mountain ranges and mountain ranges extending in a north-south direction, instead of serving as a barrier, it facilitated plant species to move to more propitious areas and then spread to where they are today.
With the general warming of the atmosphere and the consequent retreat of the ice, the surviving Tertiary flora tries to reconquer its area of distribution in southern Europe. But the new postglacial climate is drier than that of the Tertiary, and faced with these new environmental demands, the primitive tropical European flora evolves and gives rise to the current sclerophyll flora of the Mediterranean basin. Thus, the Mediterranean flora and the Macaronesian flora have a common origin.
At the same time, isolated from the mainland, the Macaronesian Tertiary flora evolved independently, giving rise to numerous endemic species. Indeed, it is worth noting that 50-55% of the vascular flora of the Canary Islands are species exclusive to the archipelago, and that this proportion increases on more distant islands such as Cape Verde, Azores or Madeira. The Macaronesian laurel forest consists of about 25 trees, which are around 35 if the species that survived in nearby areas of Eurasia are added, while in the Misiones laurel forest, there are more than 100 tree species, it is likely that the Atlantic laurel forest of the Tertiary equaled the number of species of the missionary laurel forest.
Composition and structure
In its natural environment it is an ecoregion of umbrophilous forest oozing humidity and low light, the soil of the Atlantic laurel forest is covered with a thick layer of organic matter where ferns, liverworts, mosses and lichens grow, which also ascend the trunks and branches. Vines, vines and lianas complete the impenetrable tangle. A cloud forest is generally a tropical or subtropical moist montane forest characterized by a high incidence of surface cloudiness, usually at the canopy level. Cloud forests often have abundant cover of mosses and vegetation, which is why they are also known as mossy forests. Cloud forests preferentially develop around mountains, where moisture introduced by forming clouds is more effectively retained. The definition of "cloud forest" It can be ambiguous, since many countries do not use this term, preferring to call them Yungas in Peru, Valdivian forest or cold jungle in Chile, Laurissilva in the Atlantic islands, Cloudy cloud forest in Mexico and occasionally subtropical and temperate forests, with meteorological conditions similar, are considered cloud forests. The closest relatives of the genera present today (ilex, laurus, laurelia, arbutus, rhododendron, prunus, erica...) appear in the Himalayas, America, South Africa, Europe, Australia and New Zealand.
Current situation of the laurel forest
Laurisilva has been greatly damaged due to its felling for timber use, both accidental and intentional burning, the opening of fields for crops, either subsistence or colonial crops in past times, and exotic timber plantations in the current situation, the opening of pastures for cattle, golf courses and tourist equipment and the introduction of exotic animal and plant species that have gradually replaced the original cover. Most of the biota is in serious danger of extinction. The species that make up the laurel forest are usually resistant and vigorous, which is why the forest regenerates easily. Its decline is due to the tremendous pressure it supports.
The best preserved and currently studied are the Valdivian laurel forest, which still has a large area, and the Misiones laurel forest, with a large number of species.
There are continuous extensions of laurel forests in the other warm-temperate and humid zones of the planet. In the eastern Mediterranean, on some islands in the Aegean Sea, the Black Sea coast of Iran and Turkey, the laurel forests that once housed remain a few such forests, taxus baccata, prunus laurocerasus etc., on the Turkish Black Sea coast to Iran.
America
North American laurel forests occupy a large area of the East Coast and the Gulf of Mexico in Mississippi, Carolina, and Florida in the United States, and West Coast laurel forests in California, Oregon, and Canada from San Francisco, by Ucluelet, Vancouver, the offshore islands and the southern coast of Alaska, which gradually succeed each other until they become coniferous forests. During the Miocene, California and Baja California were covered by forests of three species of laurel-leaved oaks and other species of the laurel family: Nectandra, Ocotea, Persea, and Umbellularia. Only one species in the laurel family, Umbellularia californica, still remains in California today.
In Central America, laurel forests are the most common type of cloud forest. They are found in mountainous areas of almost all Central American countries. Normally at more than 1,000 m altitude. In the Sierra de las Minas, Guatemala, the largest and northernmost cloud forest in Central America is located. In some areas of southeastern Honduras there are also cloud forests, the largest of which are located along the border with Nicaragua. In Nicaragua, the cloud forests occur in the border area with Honduras, and most of them were cleared to grow coffee; there are still laurel forests on some hills in the north. The Mombacho volcano is the only cloud forest on the Pacific coast of Central America. In Costa Rica there are laurel forests in the Tilarán mountain range, the so-called Monteverde cloud forest and the Arenal volcano; it also appears in the Cordillera de Talamanca.
In South America we find laurels in the Andes of Colombia, Ecuador, Peru and Venezuela. The Valdivian laurisilva extends across the south of the continent, in southern Chile and Argentina, from the Pacific Ocean coast to the Andes. Another South American laurel is the missionary laurel, in eastern Paraguay, Misiones in Argentina, and southern Brazil.
The so-called yunga groups various types of forests or jungles typically evergreen and multi-specific, which often contain numerous species of the laurel. They appear from Venezuela to northwestern Argentina, passing through Brazil, Bolivia, Colombia, Ecuador and Peru. It is discontinuously distributed in the provinces of Salta, Jujuy, Tucumán and Catamarca, generally integrating into the Sub-Andean Sierras. Its relief is varied and in the places where the Andes enter the Amazon we find areas of steep slope. The pongos are characteristic of this region, which are deep channels formed by rivers, such as the one formed by the Tarma river when it flows down towards the San Ramón valley, or the one of the Urubamba river when it passes through Machu Picchu. Many of the yungas are degraded tree formations or in the process of recovery that have not yet reached their climax vegetation, as is the case with the Fayal-Brezal of the Macaronesian laurel forest.
Africa
In Africa in the Bamenda and Adamawa plateaus on the border between Nigeria and Cameroon, those of Ethiopia and Somalia bordering xerophytic ecosystems, the laurel forests around the great lakes of Africa and the laurel forests of the interior plateau of Madagascar. They are found in mountains and hills of the Congo Basin, in Central Africa. There are also cloud forests in Madagascar and other islands in the Atlantic and Indian Oceans, and the island ecoregion called the São Tomé, Príncipe and Annobón lowland forests, has the montane or high forest on its summits, with typical plants of the Afromontane flora, like the podocarpaceous conifer Afrocarpus mannii from the heights of São Tomé.
Eurasian
Associations of bayleaf oaks Quercus and bayleaf chestnuts, Castanopsis, are common in Eurasia; the "lauro-chestnut" they form the climax vegetation along with Diospyros, rutaceae and rhododendrons in Taiwan and reach across southern China to the eastern Himalayas.
In Asia those of eastern China, southwestern coast of India and Ceylon, in Asia north of India, the laurel forest is typical of the eastern Himalayas, near Assam and Arunachal Pradesh. and in the mountains of the Indochinese peninsulas. The laurel forest stretched north of the Yangtze valley and west of the Tibetan plateau. This region is very rich in species, such as holm oaks and laurifolio oaks, ginkgo, bamboo, pine, azalea and camellia. Woods with laurel and magnolia trees can also be found, and an understory of smaller shrubs and bamboo thickets. At higher altitudes conifers dominate. Laurel (shoyojurin) and bamboo forests were the predominant vegetation in the Taiheiyo evergreen forest ecoregion of southeastern Japan's Pacific coast. Accompanied by Castanopsis, Machilus, or Quercus of bay leaf. Which were replaced in recent times by fast-growing species.
Oceania
The mountains of the coastal strip of New South Wales in Australia, laurel forests of New Guinea, New Caledonia and New Zealand. New Caledonia in an ancient fragment of the supercontinent Gondwana. New Caledonia and New Zealand were separated by continental drift from Australia 85 million years ago. The islands still preserve flora and fauna that originated in Gondwana and later spread to the continents of the southern hemisphere.
The laurel forests of Australia, New Caledonia and New Zealand have a good number of species related to other Valdivian laurel forests, through the connection of the Antarctic flora, such as the gymnosperms podocarpus and the deciduous nothofagus. Corynocarpus laevigatus is called New Zealand laurel, Laurelia novae-zelandiae belongs to the same genus as Laurelia sempervirens. The niaouli tree grows in Australia, New Caledonia and New Zealand.
Macaronesian
The Atlantic laurel forest extends over the Macaronesian islands (especially in the Azores, Madeira and the Canary Islands) where it is called monteverde.
The island of La Palma has the first World Reserve of the Biosphere of the Canary Archipelago and a UNESCO Heritage Site since in 1983, the international organization declared the 511 hectares of the El Canal y Los Tilos estate Reserve of the Biosphere to safeguard the Macaronesian laurel ecosystem. On the other hand, in the center of the island of La Gomera, in the Garajonay National Park, declared a World Heritage Site by UNESCO, with 3,984 hectares (10 percent of the total area of the island), there is a of the largest laurel forests. In both cases, it is a living relic of the jungle that 65 million years ago covered vast areas of the Earth.
Unlike the vegetation of other islands, such as the laurel forests of New Guinea, New Zealand and New Caledonia, the Macaronesian laurel forest originates from continental lands that have adapted to their present location. This means that most species have always been adapted to their predation by herbivores. Thus, after the introduction of large herbivores in recent historical times, the majority of the flora already had the means to defend itself from predation, suffering minor damage compared to that suffered by the forests of other islands or even plants present in Macaronesia, arose when there were no longer large herbivores.
Mediterranean area
Although the Atlantic laurel forest is more abundant in the Macaronesian archipelagos, where the climate has hardly fluctuated since the Tertiary, there are small representations and a contribution in species to the oceanic and Mediterranean environment of Europe, Asia Minor and the West and North Africa sheltered in microenvironments with a favorable climate. That is, in the coastal mountainous massifs. These "islands" Continentals, both in Eurasia and Africa, in some cases were genuine islands in the Tertiary and in others simply ice-free areas. Although with the closure of the Strait of Gibraltar, the laurel species could have repopulated the Iberian Peninsula again, once again distributing to the north together with other specifically African species, the change to a drier and more seasonal climate prevented them, in general, from occupying their space. former.
The coastal mountain ranges of Algeciras (in the forests, called canutos, of the Los Alcornocales natural park), Monchique or Sintra are bioclimatic enclaves where subtropical vegetation is mixed with both European and North African Mediterranean taxa, coexisting with species of vegetation Mediterranean, adapted to this habitat, along with others typical of the Macaronesian laurel forest. Thus, the ivy, a climber or vine that is well represented in a good part of Europe, is the most important example of a species that once again recovered its previous territory after the ice ages. The parrot (Prunus lusitanica), the only tree that survives as a relict in some Iberian torrents, especially in the western part of the peninsula, especially in Extremadura, and somewhat less so in the Northeast. In other cases it is the presence of the Mediterranean laurel (Laurus nobilis) the tree that, due to its relationship with the true island laurels, provides an indication of where the laurel was found. This species, which also survives autochthonously in Morocco, Italy, Greece and the Mediterranean islands, is found in some Mediterranean torrents of the Iberian Peninsula, such as those of the Los Alcornocales natural park (Cádiz), where it forms forests called there joints They also appear in coastal mountains of Catalonia, being the Massif of les Cadiretes (Gerona) the one that keeps the best laurel groves, and in some patches of the Valencian Community. The island of Cortegada in Galicia, famous for its large forest of laurels, it must be said that these are not native to the island, since such a forest originated spontaneously from laurels that were planted after the original vegetation had been destroyed.
As for the species of the fayal-brezal, the other subtype of forest associated with the laurel in the monteverde, the faya spreads across North Africa forming fayals and the heather (tree heather) grows in the south of the Iberian Peninsula as a shrub, without reaching the dimensions that it has, for example, in the Canarian monteverde, where it presents an obvious arboreal appearance.
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