Agriculture and the environment

The huge increase in the amount of land under cultivation, the extension of pasture land into new areas and the intensification of agriculture have all led to increased environmental degradation. Natural ecosystems have been destroyed through deforestation, the ploughing up of grasslands, and the extension of the cultivated area on to marginal land and steep slopes with the consequent increase of soil erosion, degradation and desertification. The increasing use of irrigation has led to a huge increase in the demand for water and often the building of dams that have themselves further damaged ecosystems and many human communities.

Even in the long-established agricultural systems of the industrialized world where there has been no expansion in the amount of agricultural land (in Britain in the early 21^st century it covered the same amount of land as in 1860) there was considerable environmental destruction in the second half of the 20^th century. During that period in Britain almost all its lowland meadows, two-thirds of its lowland heaths, half its ancient lowland woods, bogs and wetlands and a quarter of its hedgerows (amounting to about 225,000 kilometres) were destroyed. Elsewhere the drainage of wetlands to provide agricultural land led to a steady loss in natural ecosystems – in the last century the United States lost half its wetlands. The biggest loss was in the Florida Everglades where drainage started in 1883, partly to provide land for urban development (the population of the area has risen from 11,000 to over 4 million) but mainly for sugar cane cultivation. Rivers were dredged, new canals dug and the natural drainage of the area was destroyed. The result was that sea water flowed in, the main lake was affected by eutrophication (lack of oxygen leading to the death of animal life), the peat dried out and the level of the land fell by a third of a metre a year. Most of the wildlife, including 90% of the two and a half million wading birds, died out.

Deforestation

The clearing of natural forest has been a continuous process throughout human history as the easiest way of obtaining new agricultural land. Before agriculture about 45% of the earth’s surface was covered by forest – about a third of all those forests have been destroyed in the last 10,000 years. In many places this has been a long, slow, steady process as for example in the Mediterranean. In China too natural forests originally covered about three quarters of the land – by the early 20^th century forests were restricted to the inaccessible and mountainous areas and by the end of the 20^th century covered no more than 5% of the land. In India what is now the Thar desert in Rajasthan and Punjab was still impenetrable jungle 2000 years ago. What is clear, however, is that the pace of destruction accelerated after 1700 and increased still further in the second half of the 20^th century.

European settlement of the new lands of the Americas and Australasia triggered off forest destruction on a vast scale.
In the eastern United States and Canada half of all the forests were cleared in the 300 years after European settlement.
Australia was only settled at the end of the 18^th century but half of the original forests no longer exist and three-quarters of the rain forest has been destroyed.
In the 20^th century a clear pattern of destruction emerged. In the 19^th century industry and the railways of the United States were fuelled by timber – it was cheaper and easier to use than coal.
Timber use per head peaked in 1907 and it was replaced by new forms of domestic heating and in industry and construction by iron, steel and plastics.
Forest clearance in the industrial world is now primarily for logging and not for agricultural land.
The increase in the forest area across the industrialized world (it grew by 36 million hectares in the 1990s alone) has been achieved through the importation of timber from the developing world – for furniture and as pulp for paper.

The impact of demands from the rich world, combined with the pressure for agricultural land from a rapidly rising population, have produced a swath of destruction in the tropical forests of the world since 1950. Overall the area covered by tropical forests has fallen by almost half – from 2.8 billion hectares to 1.5 billion in the last half century. Some of the earliest destruction took place in the Philippines and Indonesia (mainly to meet Japanese demands) so that in the former country only 3% of the original forest cover is now left. Overall in Asia about nine-tenths of the original forests have been destroyed. The scale of destruction in west Africa was even faster with clearance rates of around 15% a year in some countries. In Ivory Coast only a fortieth of the original forests still survive and in Nigeria only a seventh are left.

From the 1970s much of the destruction was concentrated in Amazonia, which contains about 40% of the remaining tropical forest in the world.
It was a way of defusing social tensions by giving land to landless labourers – it was ‘a land without men for men without land’.
Roads were built into the forests (the population along the Brasilia-Belem road rose from 200,000 when it was opened in 1960 to two million within a decade) so that logging could begin and land be cleared for settlement and plantations.
In tropical forests most of the nutrients are held not in the soil (which is poor) but in the trees and plants. The land is usually cleared by peasant farmers and the burning of the forest cover helps provide nutrients for a few years.
The soil is soon exhausted and the peasants sell out to large landowners and move on to new land.
The large landowners create large cattle ranches on the poor grassland which is all the soil will then support.
Nearly all the ranches established in the Amazon area before 1978 had been abandoned by the mid-1980s.
By the early 21^st century at least a fifth of the original forest had disappeared.
A satellite survey published in Nature in late 2005 suggested that because ‘selective logging’ (the removal of a few key trees such as mahogany) badly degraded the surrounding area the level of destruction each year could be twice that previously estimated.

Overall the rate of tropical forest destruction across the world in the early 21^st century was estimated to be on average 86,000 hectares a day (an area larger than New York City) or 31 million hectares a year (an area larger than Poland). At this rate the world’s tropical forests will be destroyed by the middle of the century at the latest. Tropical forest clearance involves the destruction of an entire ecosystem and these forests contain about half of all the plant and animal species on the planet (about 30 million different species). The actual rate of species loss is unknown but the best estimate would suggest about 50,000 a year, most of whom were unknown to science when they became extinct. Tropical forest destruction can also have a significant impact on the climate. When vegetation cover is removed, solar energy, instead of being partly absorbed by the trees, is reflected from the nearly bare ground, increasing temperatures, drying the soil, creating dust in the atmosphere and helping to stop rain clouds forming. Estimates suggest that about 260,000 square kilometers of forest needs to be cleared before these effects are noticeable on a significant scale. In the last century about four times this area has been cleared in west Africa and the consequences have become apparent. Rainfall in the Sahel and parts of sub-Saharan Africa is now a third less than it was a century ago, with over three-quarters of the years being highly arid. Similar effects are now being felt across Amazonia.

Since the 1980s there have been a number of attempts to control deforestation but they have been almost totally unsuccessful.
The fundamental problem is that for many countries timber exports are one of their few sources of export earnings in a world trade system that is already structured against them.
Effective monitoring of logging is difficult – about a third of Britain’s timber imports come from illegal logging.
Even when it is claimed that ‘sustainable’ logging takes place (where one tree is replanted for every tree cut down) the richness of a tropical forest is usually replaced by a monoculture of quick-growing trees such as eucalyptus.

A Green History of the World Part 13

Agriculture and the environment

Soil erosion

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