Rewilding (conservation biology)

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https://en.wikipedia.org/wiki/Rewilding_(conservation_biology)

 

A wildlife crossing structure on the Trans-Canada Highway in Banff National Park, Canada. Wildlife-friendly overpasses and underpasses have helped restore connectivity in the landscape for wolves, bears, elk, and other species.

Rewilding is large-scale conservation aimed at restoring and protecting natural processes and core wilderness areas, providing connectivity between such areas, and protecting or reintroducing apex predators and keystone species. Rewilding projects may require ecological restoration or wilderness engineering, particularly to restore connectivity between fragmented protected areas, and reintroduction of predators and keystone species where extirpated. The ultimate goal of rewilding efforts is to create ecosystems requiring passive management by limiting human control of ecosystems. Successful long term rewilding projects should be considered to have little to no human-based ecological management, as successful reintroduction of keystone species creates a self-regulatory and self-sustaining stable ecosystem, with near pre-human levels of biodiversity. 

Origin

The word rewilding was coined by conservationist and activist Dave Foreman, one of the founders of the group Earth First! who went on to help establish both the Wildlands Project (now the Wildlands Network) and the Rewilding Institute. The term first occurred in print in 1990 and was refined by conservation biologists Michael Soulé and Reed Noss in a paper published in 1998. According to Soulé and Noss, rewilding is a conservation method based on "cores, corridors, and carnivores." The concepts of cores, corridors, and carnivores were developed further in 1999. Dave Foreman subsequently wrote the first full-length exegesis of rewilding as a conservation strategy.

More recently, anthropologist Layla AbdelRahim offered a new definition of rewilding: "Wilderness is ... a cumulative topos of diversity, movement, and chaos, while wildness is a characteristic that refers to socio-environmental relationships". According to her, because civilization is a constantly growing enterprise, it has completely colonized the earth and imperiled life on the planet. Therefore, rewilding can start only with a revolution in the anthropology that constructs the human as predator.

History

Rewilding was developed as a method to preserve functional ecosystems and reduce biodiversity loss, incorporating research in island biogeography and the ecological role of large carnivores. In 1967, The Theory of Island Biogeography by Robert H. MacArthur and Edward O. Wilson established the importance of considering the size and isolation of wildlife conservation areas, stating that protected areas remained vulnerable to extinctions if small and isolated. In 1987, William D. Newmark's study of extinctions in national parks in North America added weight to the theory. The publications intensified debates on conservation approaches. With the creation of the Society for Conservation Biology in 1985, conservationists began to focus on reducing habitat loss and fragmentation.

Elements required for successful rewilding

Rewilding is important on land but perhaps more important is where land meets the water. Dam removal is the first of many steps in the process of rewilding in the riverine ecosystems. However, there are problems that should be addressed before, during, and after the dam removal. The problems are the sediments that have built up and wash out filling in spawning beds should be controlled and directed, then eliminating any and all clear cutting of trees near river banks as it raises the temperature of the water, and stopping industrial discharges for obvious reasons. At 90 different dam sites it has been confirmed that after a dam is built the ecosystem does rebound. However, the trend will eventually slow, stop and in some cases decline. This is often due to anthropogenic chemical, light, and noise pollution as the large bodies of water draw human activity and recreation. Nemecek writes that, "researchers found that the number of species within any given area dropped by 50%. Lastly, food sources for native animals and fish need to be introduced so as to improve the long-term sustainability of native species and curtail and/or eliminate the introduction of invasive species. 

Key species

The beaver is by far the most important element of a riverine ecosystem. Firstly, the dams they build create micro ecosystems that can be used as spawning beds for salmon and collect invertebrates for the salmon fry to feed on. The dams, again built by beavers, create wetlands for plant, insect, and bird life. Specific trees, alder, birch, cottonwood, and willow are important to beaver's diets and must be encouraged to grow in areas accessible by the animals. In terms of seeding the birds can do much of the rest. These animals have a trickle down effect as they create ecosystems that have the potential to grow exponentially. 

Major rewilding projects

Between 800 and 1150 wild koniks live in the Oostvaardersplassen, a 56 km² rewilding project in the Netherlands

Both grassroots groups and major international conservation organizations have incorporated rewilding into projects to protect and restore large-scale core wilderness areas, corridors (or connectivity) between them, and apex predators, carnivores, or keystone species (species which interact strongly with the environment, such as elephant and beaver). Projects include the Yellowstone to Yukon Conservation Initiative in North America (also known as Y2Y) and the European Green Belt, built along the former Iron Curtain; transboundary projects, including those in southern Africa funded by the Peace Parks Foundation; community-conservation projects, such as the wildlife conservancies of Namibia and Kenya; and projects organized around ecological restoration, including Gondwana Link, regrowing native bush in a hotspot of endemism in southwest Australia, and the Area de Conservacion Guanacaste, restoring dry tropical forest and rainforest in Costa Rica. European Wildlife, established in 2008, advocates the establishment of a European Centre of Biodiversity at the German–Austrian–Czech borders.

In North America, another major project aims to restore the prairie grasslands of the Great Plains. The American Prairie Foundation is reintroducing bison on private land in the Missouri Breaks region of north-central Montana, with the goal of creating a prairie preserve larger than Yellowstone National Park. Dam removal has led to the restoration of many river systems in the Pacific Northwest. This has been done in an effort to restore salmon populations specifically but with other species in mind. "These dam removals provide perhaps the best example of large-scale environmental remediation in the twenty-first century. This restoration, however, has occurred on a case-by-case basis, without a comprehensive plan. The result has been to put into motion ongoing rehabilitation efforts in four distinct river basins: the Elwha and White Salmon in Washington and the Sandy and Rogue in Oregon."

An organization called Rewilding Australia has formed which intends to restore various marsupials and other Australian animals which have been extirpated from the mainland, such as Eastern quolls and Tasmanian devils.

Projects in Europe

European bison (Bison bonasus); Europe's largest living land animal. The European bison was driven to extinction in the wild in 1927; in the mid-20th century and early 21st century, the bison has been re-introduced into the wild. The bison stands nearly 2 metres tall and weighs as much as 1,000 kg.

In the 1980s, the Dutch government began introducing proxy species in the Oostvaardersplassen nature reserve in order to recreate a grassland ecology. Though not explicitly referred to as rewilding, nevertheless many of the goals and intentions of the project were in line with those of rewilding. The reserve is considered somewhat controversial due to the lack of predators and other native megafauna such as wolves, bears, lynx, elk, boar, and wisent.

Since the 1980's, 8.5 million trees have been planted in the United Kingdom in an area of the midlands around the villages of Moira and Donisthorpe, close to Leicester. The area is called The National Forest. Another, larger, reforestation project, aiming to plant 50 million trees is beginning in South Yorkshire, called The Northern Forest. Despite this, the UK government has been criticised for not achieving its tree planting goals. The Knepp Estate and Roy Dennis Wildlife Foundation have overseen reintroductions of extinct bird species in the UK.

In 2011, the 'Rewilding Europe' initiative was established with the aim of rewilding 1 million hectares of land in ten areas including the western Iberian Peninsula, Velebit, the Carpathians and the Danube delta by 2020, mostly abandoned farmland among other identified candidate site. The present project considers only species that are still present in Europe, such as the Iberian lynx, Eurasian lynx, wolf, European jackal, Brown bear, chamois, Spanish ibex, European bison, red deer, griffon vulture, cinereous vulture, Egyptian vulture, Great white pelican and horned viper, along with a few primitive breeds of domestic horse and cattle as proxies for the extinct tarpan and aurochs. Since 2012, Rewilding Europe is heavily involved in the Tauros Programme, which seeks to recreate the phenotype of the aurochs, the wild ancestors of domestic cattle by selectively breeding existing breeds of cattle. Many projects also employ domestic water buffalo as a grazing proxy for the extinct European water buffalo.Reviving Europe.

Historic range of the European bison.

  Maximum Holocene range

  Range during the high middle ages

  Relict 20th century populations

In 2010 and 2011, an unrelated initiative in the village of San Cebrián de Mudá (190 inhabitants) in Palencia, northern Spain released 18 European bisons (a species extinct in Spain since the Middle Ages) in a natural area already inhabited by roe deer, wild boar, red fox and grey wolf, as part of the creation of a 240-hectare "Quaternary Park". Three Przewalski horses from a breeding center in Le Villaret, France were added to the park in October 2012. Onagers and "aurochs" were planned to follow.

On 11 April 2013, eight European bison (one male, five females and two calves) were released into the wild in the Bad Berleburg region of Germany, after 300 years of absence from the region.

In 2014 the German government built a 3 km road tunnel to remove an Autobahn from the Leutratal und Cospoth nature reserve.

In 2016 and 2018, the True Nature Foundation reintroduced in total 7 European bison of the Lowland-Caucasian breeding line in Anciles Wildlife Reserve in the Parque Regional de Picos de Europa in the Cantabrian mountains in northern Spain.

Pleistocene rewilding

Pleistocene rewilding was proposed by the Brazilian ecologist Mauro Galetti in 2004. He suggested the introduction of elephants (and other proxies of extinct megafauna) from circuses and zoos to private lands in the Brazilian cerrado. In 2005, stating that much of the original megafauna of North America—including mammoths, ground sloths, and sabre-toothed cats—became extinct after the arrival of humans, Paul S. Martin proposed restoring the ecological balance by replacing them with species which have similar ecological roles, such as Asian or African elephants.

A reserve now exists for formerly captive elephants on the Brazilian Cerrado.

A controversial 2005 editorial in Nature, signed by a number of conservation biologists, took up the argument, urging that elephants, lions, and cheetahs could be reintroduced in protected areas in the Great Plains. The Bolson tortoise, discovered in 1959 in Durango, Mexico, was the first species proposed for this restoration effort, and in 2006 the species was reintroduced to two ranches in New Mexico owned by media mogul Ted Turner. Other proposed species include various camelids, equids, and peccaries.

In 1988, researcher Sergey A. Zimov established the Pleistocene Park in northeastern Siberia to test the possibility of restoring a full range of grazers and predators, with the aim of recreating an ecosystem similar to the one in which mammoths lived. Yakutian horses, reindeer, snow sheep, elk, yak and moose were reintroduced, and reintroduction is also planned for bactrian camels, red deer, and Siberian tigers. The wood bison, a close relative of the ancient bison that died out in Siberia 1000 or 2000 years ago, is also an important species for the ecology of Siberia. In 2006, 30 bison calves were flown from Edmonton, Alberta to Yakutsk and placed in the government-run reserve of Ust'-Buotama. This project remains controversial — a letter published in Conservation Biology accused the Pleistocene camp of promoting "Frankenstein ecosystems," stating that "the biggest problem is not the possibility of failing to restore lost interactions, but rather the risk of getting new, unwanted interactions instead." The authors proposed that—rather than trying to restore a lost megafauna—conservationists should dedicate themselves to restoring existing species to their original habitats.

Tropical Africa

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Tropical_Africa

 

Tropical zones in Africa and surrounding areas.

 

Although tropical Africa is mostly familiar to the West for its rainforests, this ecozone of Africa is far more diverse. While the tropics are thought of as regions with warm to hot moist climates caused by latitude and the tropical rain belt, the geology of areas, particularly mountain chains, and geographical relation to continental and regional scale winds impact the overall parts of areas, also, making the tropics run from arid to humid in West Africa. The area has very serious overpopulation problems.

Overview

Tropical rainforests are tropical moist forests of semi-deciduous varieties distributed across nine West African countries. Institute for Sea Research conducted a temperature record dating back to 700,000 years ago. Several conservation and development demographic settings are such that the most loss of rain forests has occurred in countries of higher population growth. Lack of dependable data and survey information in some countries has made the account of areas of unbroken forest and/or under land use change and their relation to economic indicators difficult to ascertain. Hence, the amount and rate of deforestation in Africa are less known than other regions of tropics.

The term deforestation refers to the complete obstruction of forest canopy cover for means of agriculture, plantations, cattle-ranching, and other non-forest fields. Other forest use changes for example are forest disintegration (changing the spatial continuity and creating a mosaic of forest blocks and other land cover types), and dreadful conditions (selective logging of woody species for profitable purposes that affects the forest subfloor and the biodiversity). The general meaning to the term deforestation is linked not only to the value system but the type of measurement designed to assess it. Thus, the same interpretations of deforestation cause noticeable changes in the estimate of forests cleared.

One reason for forest depletion is to grow cash crops. Nine West African countries depend on cash crop exports. Products like gum, copal, rubber, cola nuts, and palm oil provide rather steady income revenue for the West African countries. Land use change spoils entire habitats with the forests. Converting forests into timber is another cause of deforestation. Over decades, the primary forest product was commercial timber. Urbanized countries account for a great percentage of the world's wood consumption, that increased greatly between 1950 and 1980. Simultaneously, preservation measures were reinforced to protect European and American forests. Economic growth and growing environmental protection in industrialized European countries made request for tropical hardwood become strong in West Africa. In the first half of the 1980s, an annual forest loss of 7,200 km² (2,800 sq mi) was note down along the Gulf of Guinea, a figure equivalent to 4-5 per cent of the total remaining rain forest area. By 1985, 72% of West Africa's rainforests had been transformed into fallow lands and an additional 9% had been opened up by timber exploitation.

Tropical timber became a viable choice to European wood following World War II, as trade with East European countries stop and timber noticeably became sparse in western and southern Europe. Despite efforts to promote lesser known timber species use, the market continued to focus on part of the usable timber obtainable. West Africa was prone to selective harvesting practices; while conservationists blamed the timber industry and the farmers for felling trees, others believe rain forest destruction is connected to the problem of fuel wood. The contribution of fuel wood consumption to tree stock decline in Africa is believed to be significant. It is generally believed that firewood provides 75% of the energy used in sub-Sahara Africa. With the high demand, the consumption of wood for fuel exceeds the renewal of forest cover. 

African Pygmies living in the Dzanga-Sangha Special Reserve

 

The rain forests which remain in West Africa now merely are how they were hardly 30 years ago. In Guinea, Liberia and the Ivory Coast, there is almost no primary forest cover left unscathed; in Ghana the situation is much worse, and nearly all the rain forest are cut down. Guinea-Bissau loses 200 to 350 km² (77 to 135 sq mi) of forest yearly, Senegal 500 km² (190 sq mi) of wooded savanna, and Nigeria 6,000,050,000 of both. Liberia exploits 800 km² (310 sq mi) of forests each year.

 Extrapolating from present rates of loss, botanist Peter Raven pictures that the majority of the world's moderate and smaller rain forests (such as in Africa) could be ruined in forty years. Tropical Africa is about 18% of the world total covering 20 million km² (7.7 million sq mi) of land in West and Central Africa. The region has been facing deforestation in various degrees of intensity throughout the recent decades. The actual rate of deforestation varies from one country to another and accurate data does not exist yet. Recent estimates show that the annual pace of deforestation in the region can vary from 150 km² (58 sq mi) in Gabon to 2,900 km² (1,100 sq mi) in Cote d'Ivoire. Remaining tropical forest still cover major areas in Central Africa but are abridged by patches in West Africa.

The African Timber Organization member countries (ATO) eventually recognized the cooperation between rural people and their forest environment. Customary law gives residents the right to use trees for firewood, fell trees for construction, and collect of forest products and rights for hunting or fishing and grazing or clearing of forests for maintenance agriculture. Other areas are called "protected forests", which means that uncontrolled clearings and unauthorized logging are forbidden. After World War II, commercial exploitation increased until no West African forestry department was able of making the law. By comparison with rain forests in other places of the world in 1973, Africa showed the greatest infringement though in total volume means, African timber production accounted just one third compared to that of Asia. The difference was due to the variety of trees in Africa forests and the demand for specific wood types in Europe.

Forestry regulations in east Africa were first applied by colonial governments, but they were not strict enough to fill forest exploitation. It wasn't until the 1970s that the inadequate performance of forest regulations was recognized. The Tropical Forestry Action Plan was conceived in 1987 by the World Resources Institute in cooperation with the Food and Agriculture Organization, the United Nations Development Program (UNDP) and the World Bank with hopes of halting tropical forest destruction. In its bid to stress forest conservation and development, the World Bank provided $111,103 million in building countries, especially in Africa, to help in developing long range forest conservation and management programs meant for ending deforestation. 

Region protection

Many African countries are in economic and political change, overwhelmed by conflict, making various movements of forest exploitation to maintained forest management and production more and more complicated. 

Forest legislation of ATO member countries aim to promote the balanced utilization of the forest domain and of wildlife and fishery in order to increase the input of the forest sector to the economic, social, cultural and scientific development of the country.

Habitats

The tropical environment is rich in terms of biodiversity. Tropical African forest is 18 percent of the world total and covers over 3.6 million square kilometers of land in West, East and Central Africa. This total area can be subdivided to 2.69 million square kilometers (74%) in Central Africa, 680,000 square kilometers (19%) in West Africa, and 250,000 square kilometers (7%) in East Africa.^[2] In West Africa, a chain of rain forests up to 350 km long extends from the eastern border of Sierra Leone all the way to Ghana. In Ghana the forest zone gradually dispels near the Volta river, following a 300 km stretch of Dahomey savanna gap. The rain forest of West Africa continues from east of Benin through southern Nigeria and officially ends at the border of Cameroon along the Sanaga river.

Ituri Rainforest

 

Semi-deciduous rainforests in West Africa began at the fringed coastline of Guinea Bissau (via Guinea) and run all the way through the coasts of Sierra Leone, Liberia, Ivory Coast, Ghana, continuing through Togo, Benin, Nigeria and Cameroon, and ending at the Congo Basin. Rain forests such as these are the richest, oldest, most prolific, and most complex systems on earth, are dying, and in turn are upsetting the delicate ecological balance. This may disturb global hydrological cycles, release vast amounts of greenhouse gases into the atmosphere, and lessen the planet's ability to store excess carbon. 

The rain forest vegetation of the Guinea-Congolian transition area, extending from Senegal to western Uganda are constituted of two main types: The semi-deciduous rain forest characterized by a large number of trees whose leaves are left during dry season. It appears in areas where the dry period (rainfall below about 100 mm) reach three months. Then, the evergreen or the semi-evergreen rain forest, climatically adapted to somewhat more humid conditions than the semi-deciduous type and is usually there in areas where the dry period is shorter than two months. This forest is usually richer in legumes and variety of species and its maximum development is around the Bight of Biafra, from Eastern Nigeria to Gabon, and with some large patches leaning to the west from Ghana to Liberia and to the east of Zaïre-Congo basin. 

Judging against rain forest areas in other continents, most of the African rainforest is rather dry and receives between 1600 and 2000 mm of rainfall per year. Areas receiving more rain than this mainly are in coastal areas. The circulation of rainfall throughout the year remains less than other rain forest regions in the world. The average monthly rainfall in nearly the whole region remains under 100 mm throughout the year. The variety of the African rain forest flora is also less than the other rain forests. This lack of flora has been credited to several reasons such as the gradual infertility since the Miocene, severe dry periods during Quaternary, or the refuge theory of the cool and dry climate of tropical Africa during the last severe ice age of about 18000 years ago.

A recent vegetation map of Africa published by UNESCO and the main vegetation features of Central African rain forest divides the area into the following categories: . This type of forest shows no substantial seasonal behavior. At the border of the central basin is the mesophilous semi-deciduous forest that is mixed with deciduous and evergreen trees in the upper-stratum, unusual age distribution, continuous shrub stratum at the lower canopy, and a more marked seasonality. 

Secondary forests

Beyond the forest reserves, a great deal of the remaining part of Central African rain forest on well drained soils are old secondary forests. There also exist younger secondary forests dominated by parasol trees, Musanga cecropioides, the most abundant and characteristic secondary forest in Africa. Such trees are found in upper layers of secondary growth along the old road networks in Zaïre . The dispersal of secondary forests are important in regional study as they show different floristic and faunistic characteristics than primary forests, and represent centers of human activity and history of land-use changes.

Non-forest

The nart comprises degraded lands, irregular agriculture and plantations., and deforested lands and fragmented forests. Plantations have a geometrical lay-out with uniform canopy-cover and follow a different vegetation cycle as their adjacent features. The areas are located near the transportation networks and are subjugated by economic tree crops such as cacao, rubber, oil palms and Kola. 

Swamp and flooded forests

Swamp forest, inundated forests in flood plains, and riparian forests are found here. Swamp forests are found widely in the Zaïre basin and throughout the Congo basin where conditions are appropriate. In most areas, swamp forests is like in appearance to rain forest and the tallest trees attain a height of 45 m. The main canopy is often irregular and open, sometimes resembling the secondary forests caused by disturbance The forest has a variety in endemic flora but it is inadequate in species. Recently, large areas of swamp forests have been cleared for rice farming. Swamp forests in Zaïre, Congo and other lowland forests have seasonal variations that to the level of forest inundation. 

Conservation

In colonial rule, governments planned only one way to promote conservation. In Nigeria for example, the government introduced forest protection regulatory measures by classification of some forest areas, licensing requirements, and the apprehension and prosecution of offenders. Ghana issued classification permits to firms and executed log export restrictions. The Ivory Coast and Cameroon introduced log supply quotas, as Liberia did.

This trade product is "raw" lumber. Trees native to the West African rainforest from which timber is exported include limba, emeri, obeche and opepe as well as the exotic species gmelina, teak, and pinus. 

Fauna

African forest elephant

 

The Tropical African rainforest has rich fauna, commonly smaller mammal species rarely seen by humans. New species continually are being found. For instance, in late 1988 an unknown shrub species was discovered on the shores of the Median River in Western Cameroon. Since then many species have become extinct. However, undisturbed rainforests are some of the richest habitats of animal species. Today, undisturbed rainforests are remnant, but rare. Timber extraction not only changes the edifice of the forest, it affects the tree species spectrum by removing economically important species and terminates other species in the process. The species that compose African rainforests are of different evolutionary ages because of the contraction and expansion of the rainforest in response to global climatic fluctuations. In Tropical Africa about 8,500 plant species have been noted and 403 species of orchids note down. The pygmy hippopotamus, the giant forest hog, the water chevrotain and a number of insectivores, rodents and bats, tree frogs, bird species inhabit the area. These species, along with a diversity of fruits and insects, make a special habitat. Top canopy monkey species, the red colobus, and others, already have disappeared from much of Tropical Africa's forest. 

Species unfamiliar to the changes in forest structure for industrial use might not survive. If timber use continues and an increasing amount of farming occurs, it could lead to the mass killing of animal species. The home of nearly half of the world's animals and plant species are tropical rainforests. The rain forests provide possible economic resource for over-populated developing countries. Despite the stated need to save the West African forests, there are divergence in how to work. In April 1992, countries with some of the largest surviving tropical rain forests banned a rainforest protection plan proposed by the British government. It aimed at finding endangered species of tropical trees in order to control trade in them. Experts estimate that the rainforest of West Africa, at the present trend of deforestation, may disappear by the year 2020.

Africa's rainforest, like many others emergent in the world, has a special significance to the indigenous cultures who have occupied them for millennia.

Recent news: History of Tropical Africa

In early 2007, scientists created an entirely new proxy to determine annual mean air temperature on land—based on molecules from the cell membrane of soil inhabiting bacteria. Recently, Scientists from the NIOZ, Royal Netherlands Institute for Sea Research conducted a temperature record dating back to 25,000 years ago. In concord with the German colleague of the University of Bremen, this detailed record shows the history of land temperatures based on the molecular fossils of soil bacteria. When applying this to the outflow core of the Congo River, the core contained eroded land material and microfossils from marine algae. That concluded that the land environment of tropical Africa was cooled more than the bordering Atlantic Ocean during the last ice-age. Since the Congo River drains a large part of tropical central Africa, the land derived material gives an integrated signal for a very large area. These findings further enlighten in natural disparities in climate and the possible costs of a warming earth on precipitation in central Africa.

Scientists discovered a way to measure sea temperature—based on organic molecules from algae growing off the surface layer of the Ocean. These organisms acclimatize the molecular composition of their cell membranes to ambient temperature to sustain regular physiological properties. If such molecules sink to the sea floor and are buried in sediments where oxygen does not go through, they can be preserved for thousands of years. The ratios between the different molecules from the algal cell membrane can approximate the past temperature of the sea surface. The new “proxy” used in this sediment core obtained both a continental and a sea surface temperature record. In comparison, both records shows that ocean surface and land temperatures behaved differently during the past 25,000 years. During the last ice age, African temperatures were 21 °C, about 4 °C lower than today, while the tropical Atlantic Ocean was only about 2.5 °C cooler. Lead author Johan Weijers and his colleagues arrived that the land-sea temperature difference has by far the largest influence on continental rainfall. The relation of air pressure to temperature strongly determines this factor. During the last ice age, the land climate in tropical Africa was drier than it is now, whereas it favors the growth of a lush rainforest.

Tropical rainforest

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Tropical_rainforest 

 

An area of the Amazon rainforest in Brazil. The tropical rainforests of South America contain the largest diversity of species on Earth.

 

Tropical rainforest climate zones (Af).

 

Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as lowland equatorial evergreen rainforest. True rainforests are typically found between 10 degrees north and south of the equator (see map); they are a sub-set of the tropical forest biome that occurs roughly within the 28-degree latitudes (in the equatorial zone between the Tropic of Cancer and Tropic of Capricorn). Within the World Wildlife Fund's biome classification, tropical rainforests are a type of tropical moist broadleaf forest (or tropical wet forest) that also includes the more extensive seasonal tropical forests.

Overview

Amazon River rain forest in Peru

 

Tropical rainforests can be characterized in two words: hot and wet. Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year. Average annual rainfall is no less than 1,680 mm (66 in) and can exceed 10 m (390 in) although it typically lies between 1,750 mm (69 in) and 3,000 mm (120 in). This high level of precipitation often results in poor soils due to leaching of soluble nutrients in the ground. 

Tropical rainforests exhibit high levels of biodiversity. Around 40% to 75% of all biotic species are indigenous to the rainforests. Rainforests are home to half of all the living animal and plant species on the planet. Two-thirds of all flowering plants can be found in rainforests. A single hectare of rainforest may contain 42,000 different species of insect, up to 807 trees of 313 species and 1,500 species of higher plants. Tropical rainforests have been called the "world's largest pharmacy", because over one quarter of natural medicines have been discovered within them. It is likely that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests.

Tropical rainforests are among the most threatened ecosystems globally due to large-scale fragmentation as a result of human activity. Habitat fragmentation caused by geological processes such as volcanism and climate change occurred in the past, and have been identified as important drivers of speciation. However, fast human driven habitat destruction is suspected to be one of the major causes of species extinction. Tropical rain forests have been subjected to heavy logging and agricultural clearance throughout the 20th century, and the area covered by rainforests around the world is rapidly shrinking.

History

Tropical rainforests have existed on earth for hundreds of millions of years. Most tropical rainforests today are on fragments of the Mesozoic era supercontinent of Gondwana. The separation of the landmass resulted in a great loss of amphibian diversity while at the same time the drier climate spurred the diversification of reptiles. The division left tropical rainforests located in five major regions of the world: tropical America, Africa, Southeast Asia, Madagascar, and New Guinea, with smaller outliers in Australia. However, the specifics of the origin of rainforests remain uncertain due to an incomplete fossil record. 

Other types of tropical forest

Several biomes may appear similar-to, or merge via ecotones with, tropical rainforest:

Moist seasonal tropical forest

Daintree "rainforest" in Queensland is actually a seasonal tropical forest.

 

Moist seasonal tropical forests receive high overall rainfall with a warm summer wet season and a cooler winter dry season. Some trees in these forests drop some or all of their leaves during the winter dry season, thus they are sometimes called "tropical mixed forest". They are found in parts of South America, in Central America and around the Caribbean, in coastal West Africa, parts of the Indian subcontinent, and across much of Indochina.

Montane rainforests

These are found in cooler-climate mountainous areas, becoming known as cloud forests at higher elevations. Depending on latitude, the lower limit of montane rainforests on large mountains is generally between 1500 and 2500 m while the upper limit is usually from 2400 to 3300 m.

Flooded rainforests

Tropical freshwater swamp forests, or "flooded forests", are found in Amazon basin (the Várzea) and elsewhere. 

Forest structure

Rainforests are divided into different strata, or layers, with vegetation organized into a vertical pattern from the top of the soil to the canopy. Each layer is a unique biotic community containing different plants and animals adapted for life in that particular strata. Only the emergent layer is unique to tropical rainforests, while the others are also found in temperate rainforests.

Forest floor

Western lowland gorilla

 

The forest floor, the bottom-most layer, receives only 2% of the sunlight. Only plants adapted to low light can grow in this region. Away from riverbanks, swamps and clearings, where dense undergrowth is found, the forest floor is relatively clear of vegetation because of the low sunlight penetration. This more open quality permits the easy movement of larger animals such as: ungulates like the okapi (Okapia johnstoni), tapir (Tapirus sp.), Sumatran rhinoceros (Dicerorhinus sumatrensis), and apes like the western lowland gorilla (Gorilla gorilla), as well as many species of reptiles, amphibians, and insects. The forest floor also contains decaying plant and animal matter, which disappears quickly, because the warm, humid conditions promote rapid decay. Many forms of fungi growing here help decay the animal and plant waste. 

Understory layer

The understory layer lies between the canopy and the forest floor. The understory is home to a number of birds, small mammals, insects, reptiles, and predators. Examples include leopard (Panthera pardus), poison dart frogs (Dendrobates sp.), ring-tailed coati (Nasua nasua), boa constrictor (Boa constrictor), and many species of Coleoptera. The vegetation at this layer generally consists of shade-tolerant shrubs, herbs, small trees, and large woody vines which climb into the trees to capture sunlight. Only about 5% of sunlight breaches the canopy to arrive at the understory causing true understory plants to seldom grow to 3 m (10 feet). As an adaptation to these low light levels, understory plants have often evolved much larger leaves. Many seedlings that will grow to the canopy level are in the understory. 

The canopy at the Forest Research Institute Malaysia

 

Canopy layer

The canopy is the primary layer of the forest forming a roof over the two remaining layers. It contains the majority of the largest trees, typically 30–45 m in height. Tall, broad-leaved evergreen trees are the dominant plants. The densest areas of biodiversity are found in the forest canopy, as it often supports a rich flora of epiphytes, including orchids, bromeliads, mosses and lichens. These epiphytic plants attach to trunks and branches and obtain water and minerals from rain and debris that collects on the supporting plants. The fauna is similar to that found in the emergent layer, but more diverse. It is suggested that the total arthropod species richness of the tropical canopy might be as high as 20 million. Other species habituating this layer include many avian species such as the yellow-casqued wattled hornbill (Ceratogymna elata), collared sunbird (Anthreptes collaris), grey parrot (Psitacus erithacus), keel-billed toucan (Ramphastos sulfuratus), scarlet macaw (Ara macao) as well as other animals like the spider monkey (Ateles sp.), African giant swallowtail (Papilio antimachus), three-toed sloth (Bradypus tridactylus), kinkajou (Potos flavus), and tamandua (Tamandua tetradactyla).

Emergent layer

The emergent layer contains a small number of very large trees, called emergents, which grow above the general canopy, reaching heights of 45–55 m, although on occasion a few species will grow to 70–80 m tall. Some examples of emergents include: Balizia elegans, Dipteryx panamensis, Hieronyma alchorneoides, Hymenolobium mesoamericanum, Lecythis ampla and Terminalia oblonga. These trees need to be able to withstand the hot temperatures and strong winds that occur above the canopy in some areas. Several unique faunal species inhabit this layer such as the crowned eagle (Stephanoaetus coronatus), the king colobus (Colobus polykomos), and the large flying fox (Pteropus vampyrus).

However, stratification is not always clear. Rainforests are dynamic and many changes affect the structure of the forest. Emergent or canopy trees collapse, for example, causing gaps to form. Openings in the forest canopy are widely recognized as important for the establishment and growth of rainforest trees. It is estimated that perhaps 75% of the tree species at La Selva Biological Station, Costa Rica are dependent on canopy opening for seed germination or for growth beyond sapling size, for example.

Ecology

Climates

Artificial tropical rainforest in Barcelona

 

Tropical rainforests are located around and near the equator, therefore having what is called an equatorial climate characterized by three major climatic parameters: temperature, rainfall, and dry season intensity. Other parameters that affect tropical rainforests are carbon dioxide concentrations, solar radiation, and nitrogen availability. In general, climatic patterns consist of warm temperatures and high annual rainfall. However, the abundance of rainfall changes throughout the year creating distinct moist and dry seasons. Tropical forests are classified by the amount of rainfall received each year, which has allowed ecologists to define differences in these forests that look so similar in structure. According to Holdridge's classification of tropical ecosystems, true tropical rainforests have an annual rainfall greater than 2 m and annual temperature greater than 24 degrees Celsius, with a potential evapotranspiration ratio (PET) value of <0 .25.="" a="" however="" href="https://en.wikipedia.org/wiki/Tropical_forest" lowland="" most="" title="Tropical forest">tropical forests

can be classified as tropical moist or wet forests, which differ in regards to rainfall. Tropical forest ecology- dynamics, composition, and function- are sensitive to changes in climate especially changes in rainfall.

Soils

Soil types

Soil types are highly variable in the tropics and are the result of a combination of several variables such as climate, vegetation, topographic position, parent material, and soil age. Most tropical soils are characterized by significant leaching and poor nutrients, however there are some areas that contain fertile soils. Soils throughout the tropical rainforests fall into two classifications which include the ultisols and oxisols. Ultisols are known as well weathered, acidic red clay soils, deficient in major nutrients such as calcium and potassium. Similarly, oxisols are acidic, old, typically reddish, highly weathered and leached, however are well drained compared to ultisols. The clay content of ultisols is high, making it difficult for water to penetrate and flow through. The reddish color of both soils is the result of heavy heat and moisture forming oxides of iron and aluminium, which are insoluble in water and not taken up readily by plants.

Soil chemical and physical characteristics are strongly related to above ground productivity and forest structure and dynamics. The physical properties of soil control the tree turnover rates whereas chemical properties such as available nitrogen and phosphorus control forest growth rates. The soils of the eastern and central Amazon as well as the Southeast Asian Rainforest are old and mineral poor whereas the soils of the western Amazon (Ecuador and Peru) and volcanic areas of Costa Rica are young and mineral rich. Primary productivity or wood production is highest in western Amazon and lowest in eastern Amazon which contains heavily weathered soils classified as oxisols. Additionally, Amazonian soils are greatly weathered, making them devoid of minerals like phosphorus, potassium, calcium, and magnesium, which come from rock sources. However, not all tropical rainforests occur on nutrient poor soils, but on nutrient rich floodplains and volcanic soils located in the Andean foothills, and volcanic areas of Southeast Asia, Africa, and Central America.

Oxisols, infertile, deeply weathered and severely leached, have developed on the ancient Gondwanan shields. Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminium oxides by the laterization process gives the oxisols a bright red color and sometimes produces minable deposits (e.g., bauxite). On younger substrates, especially of volcanic origin, tropical soils may be quite fertile. 

Nutrient recycling

This high rate of decomposition is the result of phosphorus levels in the soils, precipitation, high temperatures and the extensive microorganism communities. In addition to the bacteria and other microorganisms, there are an abundance of other decomposers such as fungi and termites that aid in the process as well. Nutrient recycling is important because below ground resource availability controls the above ground biomass and community structure of tropical rainforests. These soils are typically phosphorus limited, which inhibits net primary productivity or the uptake of carbon. The soil contains microbial organisms such as bacteria, which break down leaf litter and other organic matter into inorganic forms of carbon usable by plants through a process called decomposition. During the decomposition process the microbial community is respiring, taking up oxygen and releasing carbon dioxide. The decomposition rate can be evaluated by measuring the uptake of oxygen. High temperatures and precipitation increase decomposition rate, which allows plant litter to rapidly decay in tropical regions, releasing nutrients that are immediately taken up by plants through surface or ground waters. The seasonal patterns in respiration are controlled by leaf litter fall and precipitation, the driving force moving the decomposable carbon from the litter to the soil. Respiration rates are highest early in the wet season because the recent dry season results in a large percentage of leaf litter and thus a higher percentage of organic matter being leached into the soil.

Buttress roots

A common feature of many tropical rainforests is the distinct buttress roots of trees. Instead of penetrating to deeper soil layers, buttress roots create a widespread root network at the surface for more efficient uptake of nutrients in a very nutrient poor and competitive environment. Most of the nutrients within the soil of a tropical rainforest occur near the surface because of the rapid turnover time and decomposition of organisms and leaves. Because of this, the buttress roots occur at the surface so the trees can maximize uptake and actively compete with the rapid uptake of other trees. These roots also aid in water uptake and storage, increase surface area for gas exchange, and collect leaf litter for added nutrition. Additionally, these roots reduce soil erosion and maximize nutrient acquisition during heavy rains by diverting nutrient rich water flowing down the trunk into several smaller flows while also acting as a barrier to ground flow. Also, the large surface areas these roots create provide support and stability to rainforests trees, which commonly grow to significant heights. This added stability allows these trees to withstand the impacts of severe storms, thus reducing the occurrence of fallen trees.

Forest succession

Succession is an ecological process that changes the biotic community structure over time towards a more stable, diverse community structure after an initial disturbance to the community. The initial disturbance is often a natural phenomenon or human caused event. Natural disturbances include hurricanes, volcanic eruptions, river movements or an event as small as a fallen tree that creates gaps in the forest. In tropical rainforests, these same natural disturbances have been well documented in the fossil record, and are credited with encouraging speciation and endemism. Human land use practices have lead to large scale deforestation. In many tropical countries such as Costa Rica these deforested lands have been abandoned and forests have been allowed to regenerate through ecological succession. These regenerating young successional forests are called secondary forests or second-growth forests. 

Biodiversity and speciation

Young orangutan at Bukit Lawang, Sumatra

 

Tropical rainforests exhibit a vast diversity in plant and animal species. The root for this remarkable speciation has been a query of scientists and ecologists for years. A number of theories have been developed for why and how the tropics can be so diverse.

Interspecific competition

Interspecific competition results from a high density of species with similar niches in the tropics and limited resources available. Species which "lose" the competition may either become extinct or find a new niche. Direct competition will often lead to one species dominating another by some advantage, ultimately driving it to extinction. Niche partitioning is the other option for a species. This is the separation and rationing of necessary resources by utilizing different habitats, food sources, cover or general behavioral differences. A species with similar food items but different feeding times is an example of niche partitioning.

Pliestocene refugia

The theory of Pleistocene refugia was developed by Jürgen Haffer in 1969 with his article Speciation of Amazonian Forest Birds. Haffer proposed the explanation for speciation was the product of rainforest patches being separated by stretches of non-forest vegetation during the last glacial period. He called these patches of rainforest areas refuges and within these patches allopatric speciation occurred. With the end of the glacial period and increase in atmospheric humidity, rainforest began to expand and the refuges reconnected. This theory has been the subject of debate. Scientists are still skeptical of whether or not this theory is legitimate. Genetic evidence suggests speciation had occurred in certain taxa 1–2 million years ago, preceding the Pleistocene.

Human dimensions

Habitation

Tropical rainforests have harboured human life for many millennia, with many Indian tribes in South- and Central America, who belong to the Indigenous peoples of the Americas, the Congo Pygmies in Central Africa, and several tribes in South-East Asia, like the Dayak people and the Penan people in Borneo. Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on a seasonal basis but dwelt primarily in adjacent savanna and open forest environments where food is much more abundant. Other people described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest.

Indigenous peoples

Members of an uncontacted tribe encountered in the Brazilian state of Acre in 2009

 

A variety of indigenous people live within the rainforest as hunter-gatherers, or subsist as part-time small scale farmers supplemented in large part by trading high-value forest products such as hides, feathers, and honey with agricultural people living outside the forest. Peoples have inhabited the rainforests for tens of thousands of years and have remained so elusive that only recently have some tribes been discovered. These indigenous peoples are greatly threatened by loggers in search for old-growth tropical hardwoods like Ipe, Cumaru and Wenge, and by farmers who are looking to expand their land, for cattle(meat), and soybeans, which are used to feed cattle in Europe and China. On 18 January 2007, FUNAI reported also that it had confirmed the presence of 67 different uncontacted tribes in Brazil, up from 40 in 2005. With this addition, Brazil has now overtaken the island of New Guinea as the country having the largest number of uncontacted tribes. The province of Irian Jaya or West Papua in the island of New Guinea is home to an estimated 44 uncontacted tribal groups.

Pygmy hunter-gatherers in the Congo Basin in 2014

 

The pygmy peoples are hunter-gatherer groups living in equatorial rainforests characterized by their short height (below one and a half meters, or 59 inches, on average). Amongst this group are the Efe, Aka, Twa, Baka, and Mbuti people of Central Africa. However, the term pygmy is considered pejorative so many tribes prefer not to be labeled as such.

Some notable indigenous peoples of the Americas, or Amerindians, include the Huaorani, Ya̧nomamö, and Kayapo people of the Amazon. The traditional agricultural system practiced by tribes in the Amazon is based on swidden cultivation (also known as slash-and-burn or shifting cultivation) and is considered a relatively benign disturbance. In fact, when looking at the level of individual swidden plots a number of traditional farming practices are considered beneficial. For example, the use of shade trees and fallowing all help preserve soil organic matter, which is a critical factor in the maintenance of soil fertility in the deeply weathered and leached soils common in the Amazon.

There is a diversity of forest people in Asia, including the Lumad peoples of the Philippines and the Penan and Dayak people of Borneo. The Dayaks are a particularly interesting group as they are noted for their traditional headhunting culture. Fresh human heads were required to perform certain rituals such as the Iban "kenyalang" and the Kenyah "mamat". Pygmies who live in Southeast Asia are, amongst others, referred to as "Negrito". 

Resources

Cultivated foods and spices

Yam, coffee, chocolate, banana, mango, papaya, macadamia, avocado, and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 1990s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mango. Central American coffee exports were worth US$3 billion in 1970. Much of the genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit, compared to only 20 for temperate forests. Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985.

Ecosystem services

In addition to extractive human uses, rain forests also have non-extractive uses that are frequently summarized as ecosystem services. Rain forests play an important role in maintaining biological diversity, sequestering and storing carbon, global climate regulation, disease control, and pollination. Half of the rainfall in the Amazon area is produced by the forests. The moisture from the forests is important to the rainfall in Brazil, Paraguay, Argentina Deforestation in the Amazon rainforest region was one of the main reason that cause the severe Drought of 2014-2015 in Brazil.

 

Tourism

Canopy walkway for seeing the diverse tropical forest in Costa Rica

 

Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects.

• In recent years ecotourism in the tropics has increased. While rainforests are becoming increasingly rare, people are travelling to nations that still have this diverse habitat. Locals are benefiting from the additional income brought in by visitors, as well areas deemed interesting for visitors are often conserved. Ecotourism can be an incentive for conservation, especially when it triggers positive economic change. Ecotourism can include a variety of activities including animal viewing, scenic jungle tours and even viewing cultural sights and native villages. If these practices are performed appropriately this can be beneficial for both locals and the present flora and fauna.
• An increase in tourism has increased economic support, allowing more revenue to go into the protection of the habitat. Tourism can contribute directly to the conservation of sensitive areas and habitat. Revenue from park-entrance fees and similar sources can be utilised specifically to pay for the protection and management of environmentally sensitive areas. Revenue from taxation and tourism provides an additional incentive for governments to contribute revenue to the protection of the forest.
• Tourism also has the potential to increase public appreciation of the environment and to spread awareness of environmental problems when it brings people into closer contact with the environment. Such increased awareness can induce more environmentally conscious behavior. Tourism has had a positive effect on wildlife preservation and protection efforts, notably in Africa but also in South America, Asia, Australia, and the South Pacific.
  

Conservation

Threats

Deforestation

Mining and drilling

The Ok Tedi Mine in southwestern Papua New Guinea

 

Deposits of precious metals (gold, silver, coltan) and fossil fuels (oil and natural gas) occur underneath rainforests globally. These resources are important to developing nations and their extraction is often given priority to encourage economic growth. Mining and drilling can require large amounts of land development, directly causing deforestation. In Ghana, a West African nation, deforestation from decades of mining activity left about 12% of the country's original rainforest intact.

Conversion to agricultural land

With the invention of agriculture, humans were able to clear sections of rainforest to produce crops, converting it to open farmland. Such people, however, obtain their food primarily from farm plots cleared from the forest and hunt and forage within the forest to supplement this. The issue arising is between the independent farmer providing for his family and the needs and wants of the globe as a whole. This issue has seen little improvement because no plan has been established for all parties to be aided.

Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and the heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon, utilize slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland that make forays into the rainforest. Up to 90% of the typical Yanamomo diet comes from farmed plants.

Some action has been taken by suggesting fallow periods of the land allowing secondary forest to grow and replenish the soil. Beneficial practices like soil restoration and conservation can benefit the small farmer and allow better production on smaller parcels of land. 

Climate change

The tropics take a major role in reducing atmospheric carbon dioxide. The tropics (most notably the Amazon rainforest) are called carbon sinks. As major carbon reducers and carbon and soil methane storages, their destruction contributes to increasing global energy trapping, atmospheric gases. Climate change has been significantly contributed to by the destruction of the rainforests. A simulation was performed in which all rainforest in Africa were removed. The simulation showed an increase in atmospheric temperature by 2.5 to 5 degrees Celsius.

Protection

Efforts to protect and conserve tropical rainforest habitats are diverse and widespread. Tropical rainforest conservation ranges from strict preservation of habitat to finding sustainable management techniques for people living in tropical rainforests. International policy has also introduced a market incentive program called Reducing Emissions from Deforestation and Forest Degradation (REDD) for companies and governments to outset their carbon emissions through financial investments into rainforest conservation.