Rainforest destruction by humans

Rainforest Destruction

Destruction of Rainforests by Man

The rainforest is one of several types of forest found throughout the tropics, and each type has different characteristics. The closed forests account for about half of the total area of tropical forest (around 62 per cent of the natural tropical forest) and comprise two types of continuous tree cover (Table 1.1). Eleven-twelfths of the closed forests, by area, are tropical moist forests and the rest are deciduous and semi-deciduous forests of various types. About two-thirds of the moist forests are tropical rainforests, composed of evergreen broadleaved trees which flourish in the high temperature and humidity of the low latitudes. The tropical moist deciduous forests (or monsoon forests) grow on the fringes of the tropical rainforests, and lose their leaves in the dry season (Ehrlich & Ehrlich, 2002).

Thesis Statement: Rainforests can never be replaced once we have lost them.

Table 1.1 Distribution of tropical forest types

Forest type

Total area (million km2)

(1)

Closed forests

12

(a)

Tropical moist forests

Tropical rainforests

7.3

Tropical moist deciduous forests

3.6

(b)

Deciduous and semi-deciduous forests

1

(2)

Open woodland

7.34

(3)

Fallow forests

4.10

(4)

Tropical forest plantations

0.115

(a)

Industrial plantations

0.071

(b)

Non-industrial plantations

0.044

TOTAL

23.55

Source: World Resources Institute (2008).

Most of the remaining tropical forests are open woodland, including shrublands and types of savanna, pasture and grassland which are partly wooded. Almost all (97 per cent) of the tropical forests which have been modified by human activity are fallow forests, areas which have recently been farmed and then abandoned or left to regenerate naturally. Only a very small area is covered by tropical forest plantations. The industrial plantations produce commercial timber, pulpwood or charcoal; the non-industrial plantations are mainly for fuel wood production or environmental protection.

Distribution

The tropical rainforests provide a discontinuous belt of green around the globe, between the tropic of Cancer (23.5° north) and the tropic of Capricorn (23.5° south). Dense rainforest is the natural climax vegetation of the hot, humid tropical zone and it flourishes particularly in the lower latitudes (between 10° north and south of the equator). Just under half of the tropical zone (49 per cent according to the World Resources Institute) is covered by forests.

Most of the tropical countries with surviving rainforests are developing countries, for which the forests provide a valuable capital asset. The total area presently covered by tropical rainforests is estimated at 12 million km2, which accounts for nearly a third of the world's forests (covering roughly 30 million km2). The distribution of forests within the tropics is uneven, reflecting the distribution of land and sea and the impacts of this on climatic boundaries. The latitudinal boundaries of the rainforest are determined mainly by precipitation, while altitudinal limits are determined more by temperature (Ellis, 2008). Some rainforests thrive beyond the 10° north and south latitudes, where high rainfall encourages forest growth. Such patches occur in Central America, the north-east coast of Australia and the great valleys of southern China.

The main rainforests today are found in three areas Latin America, Western Equatorial Africa and South-East Asia. Latin America houses the American Formation which is dominated by the Amazon and Orinoco Basins. It has over half (56 per cent) of the world total, much of it (3.31 million km2, 48 per cent of the area's total) in Brazil and the rest in Peru, Ecuador, Colombia, Venezuela and French Guiana. Amazonia is the world's largest and most important surviving rainforest. The remaining rainforests are scattered in sixteen countries in West and Central Africa (18 per cent of the world total) and South-East Asia (25 per cent of the world total). The African Formation includes the Cameroons and the Congo Basin in countries such as Gabon, Zaire and Madagascar. The Indo-Malaysian Formation in South-East Asia includes parts of western and southern India, the Far East (especially in Indonesia (Eden, 2006) particularly Borneo and Papua New Guinea -- which now has about 10 per cent of the world's remaining tropical rainforest) and north Australia.

Destruction of the Rainforest: Rates of Loss

The rainforests are under attack. These rich and complex ecosystems, which have survived millions of years of natural environmental change (indeed they have flourished through it), are now facing a fight for survival. The hands of people are inflicting more damage on the rainforests in a matter of years than the entire forces of nature have done over geological time-scales. Norman Myers, an international expert on rainforests, pointed out early in 1990 that 'at issue is the most exuberant expressions of nature that has ever graced the face of the planet during four billion years of evolution (Aiken & Leigh, 2006). Within just another 40 years at most, we may see the last remnants fall to the chainsaw and the matchbox.' The timetable is open to debate; that the fight for survival is on is not.

Shrinking Forests

We have already seen some evidence that today's rainforests are shrunken remnants of much larger forests from the ancient past. These survivors represent the outcome of long periods of climatic change; they are natural distributions, in equilibrium with today's climatic constraints in the tropics. But even that picture reflects a theoretical distribution rather than an actual pattern of vegetation on the ground. The maps of world vegetation distribution, for example, show climatic climax vegetation -- what should exist under prevailing climate, in the absence of damaging human activities, rather than what does exist. There is little doubt that many areas shown on the maps as rainforest no longer have natural forest cover, having been cleared for one reason or another. Disparities between theoretical and actual distributions of rainforest reflect human disturbance of the forest habitat. This comes in two forms. Degradation involves complete loss of the forest, which might be cut down and replaced by open woodland or agriculture. The loss is permanent. Depletion involves some change to the forest ecosystem, but not complete removal. Some plant and animal species are lost, but forest remains (albeit a much-modified forest). Natural regeneration can re-establish the forest ecosystem, given a long enough periods without further depletion. Both forms of disturbance of rainforests are widespread, but degradation poses the greatest threat.

Early Clearance

What is more certain is that clearance of the rainforest has been going on for a long time. There is evidence of clearance for agriculture at least 3,000 years ago in Africa, 7,000 years ago in South and Central America and possibly 9,000 years ago in India and New Guinea (Flenley, 2005). Traditional forms of forest clearance by burning were small-scale and localized and they had relatively little impact on the overall extent, distribution and character of the rainforests. Indeed they may even have contributed to development of the diversity of species.

More recent exploration of the rainforests, prompted by the search for commercially useful resources as well as by land hunger, started the irreversible tide of forest destruction and clearance. Early episodes were small-scale and isolated. During the fifteenth century, for example, groups of English and Dutch migrants lured by a gold rush looked to the Brazilian Amazon to meet their need for food and charcoal. Forest species were exploited for food; trees were felled and burned for charcoal. In the eighteenth century parcels of rainforest were cleared from the hills of central Minas, in eastern Brazil, to create land for cattle ranching. Soil depletion and erosion quickly followed. More widespread exploitation of the rainforests began during the eighteenth and nineteenth centuries as demand started to grow in the western world for tropical plantation crops.

Losses and Losers

Some of what is lost when rainforests are cut down or burned reflects their intrinsic value. Most of us are never likely to be able to set foot in a real rainforest, but that is not the issue. What matters is that the rainforest is important quite simply because it is there. Whether or not it has some inalienable right to survive is a debating point in moral philosophy; the fact that we would miss it if it disappeared completely is a matter of human nature and sensitivity. The extrinsic values of rainforest are easier to quantify and thus they form the basis of any evaluation of the impacts of deforestation. Whatever utilitarian interest we might have in nature's richest ecological storehouse (including many interests we were probably totally unaware of, such as using drugs and medications derived directly from rainforest products), we are all losers as the remaining forest reserves dwindle and disappear (Bunker, 2000).

Inevitably the most direct losers are the people for whom the rainforest is a home. Traditionally an estimated 50 million people live in the world's rainforests. These are mainly tribal peoples whose lifestyles and cultures are tightly interwoven with the natural cycles and processes of the forest, and who have adapted over many generations to life in the forest. Here we concentrate on the main impacts of deforestation, which include the loss of biodiversity and natural resources, loss of environmental services and possible changes to climate on the local, regional and global scales.

Species Extinction

The biggest problem associated with clearance of the world's rainforests is species extinction. Whilst the pace of extinction has doubtless speeded up in recent years, the problem itself is not new. The danger of mass extinction of rainforest species if intensive use and clearance continue was pointed out over two decades ago. Yet clearance continues, and at an ever-increasing rate. Extinction occurs when the last surviving individuals within a species die. Before that terminal point is reached, however, population levels decline as progressively more individuals die and rates of reproduction fall. Detailed biological monitoring can sometimes detect these early warning signs. Information-is available on declining populations among the 1,590 migrating bird species which fly from North America to Central America to winter each year, for example (Gomez-Pompa, et al. 1972). It suggests that bird species are disappearing at a rate of between 1 and 4 per cent a year.

Causes of Extinction

There are a number of reasons why species decline and can become extinct because of deforestation. An important underlying factor is related to the great diversity of species within the rainforest, which means that each species usually has few individuals and is thus very sensitive to change and stress. Stress comes directly through the removal of habitat and associated removal of ecological niches when a patch of rainforest is burned or felled. Fragmentation of the forest ecosystem, without complete removal -- as occurs in selective logging, for example, or when shifting cultivation encroaches on a rainforest remnant (Gray, 2000) also creates stress for the individuals which are removed or displaced. Habitat loss means a declining geographical range for each species, as well as increased competition for food and resources in the remaining areas suitable for habitation.

Species which remain are affected, too. A dwindling number of habitats means that the remaining species are forced to survive in a smaller area, facing greater competition from each other as well as from other species. Forest clearance might well remove all or part of the food chain for a species, which will create problems for those with specialist feeding requirements. Deforestation affects the whole ecosystem. Each species plays a crucial role in maintaining the delicate ecological balance of the forest system, and it is an interesting case of 'one out…all out' when clearance starts to make forest species extinct.

Something of the nature of the biological loss is captured in the statement that these irreplaceable forests are the richest source of life on earth. They are home to perhaps half the world's wild creatures. Tigers, mountain gorillas, birds of paradise, rare orchids and multicolored butterflies are some of the unique species found only in the rainforest. The world would be a poorer place without them.

Scale of Losses

Before we can establish how many species are being lost as a result of rainforest clearance, we need to know how many species the rainforests contained originally. This is not without problems, because there are many different estimates to choose from (Burley, 1985). There is a general consensus among biologists that the earth must contain something like at least 5 million species. There is also agreement that tropical rainforests contain at least half of all known species on earth, and probably a great many more. Rainforests are believed to contain about 70 per cent of all the plant species presently known on earth (Hurst, 1989). It is argued that Amazonia alone is home to an estimated 1 million species of plant and animal, including 1,600 species of birds (more than anywhere else on earth), hundreds of different tree species and as many as 40,000 species of insects.

But only about 1.5 million species are properly recorded by science today so there are a great many unknowns, particularly in rainforests. It is inevitable that most species will disappear unseen and unrecorded. United Nations Environment Programme figures for 2006 suggest that tropical species have already been reduced by 41 per cent, with most of the losses accounted for by insects. Estimation of present rates of extinction is nearly as hard as estimating original species numbers, and the estimates also vary a great deal from one study to another. Some think it probable that one species becomes extinct every half-hour as a result of the destruction of tropical rainforest, 11 making an annual total of 8,760 species. Other estimates vary between 1 and 50 species a day world-wide (between 365 and 18,250 species extinctions per year) (Jackson, 2005).