“Tropical Africa”的意思、由来-开放百科全书

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 {{Citation needed|date=March 2011}}, also, making the tropics run from arid to humid in West Africa. The area has very serious overpopulation problems.^[1]

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.^[2] 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).^[2] 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.^[2] 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 square kilometers was note down along the Gulf of Guinea, a figure equivalent to 4-5 per cent of the total remaining rain forest area.^[2] By 1985, 72 per cent of West Africa's rainforests had been transformed into fallow lands and an additional 9 per cent had been opened up by timber exploitation.^[2]

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.^[2] 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 per cent of the energy used in sub-Sahara Africa.^[2] With the high demand, the consumption of wood for fuel exceeds the renewal of forest cover.

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 of forest yearly, Senegal 500 km² of wooded savanna, and Nigeria 6,000,050,000 of both. Liberia exploits 800 km² 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 of land in West and Central Africa.^[2] 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 in Gabon to 2900 km² 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.^[2] 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.^[2] 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.^[2]

Habitats

The tropical environment is rich in terms of bio-diversity. Tropical African forest is 18 per cent 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.

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 green house 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.^[2]

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 ceropiodes, the most abundant and characteristic secondary forest in Africa. Such trees are found in upper layers of secondary regrowth 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

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 Nedian 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.^[2]:by aniketh

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 chevortain 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.^[2] 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.^[2]

Africa’s rainforest, like many others emergent in the world, has a special significance to the indigenous cultures who have occupied them for millennia.^[2]

Overview

Region protection

Habitats

Secondary forests

Non-forest

Swamp and flooded forests

Conservation

Fauna

Recent news: history of tropical Africa

Resources

See also

References

Further reading

External links