Forests: the earth's lungs

Posted: September 2009

The forest is a peculiar organism of unlimited kindness and benevolence that makes no demands for its sustenance and extends generously the products of its live activity; it offers protection to all beings offering shade even to those who destroy it."

Over the past half century the earth's vast green mantle of forests has been reduced to tattered remnants. As the world's population has grown from 2.3 billion in 1950 to over 7 billion today, some 3 billion hectares (ha) of the world's original forest cover - nearly half - has been lost. The destruction continues: in each of the last dozen years, about 14.6 million hectares of forest - an area the size of Nepal - has been cut, bulldozed, or burned.

According to the FAO Global Forest Resources Assesment 2005, the net loss in forest area at the global level during the 1990s was an estimated 94 million ha - an area larger than Venezuela and equivalent to 2.4 per cent of the world's total forests. This was a combination of an annual loss of 12.5 million ha of natural forests and an annual gain of 3.1 million ha in the form of forest plantations (see map below for details).

The 2005 FAO Assessment said that between 2000-2005, the world suffered a net loss of a further 37 million hectares (91 million acres) of forest.

Nearly 4 billion hectares of forest cover the earth's surface, roughly 30 per cent of its total land area. Though extensive, the world's forests have shrunk by some 40 per cent since agriculture began 11,000 years ago. Three-quarters of this loss occurred in the last two centuries as land was cleared to make way for farms and to meet demand for wood.

Global forest hotspots
Map of forest hotspots, showing areas undergoing high rates of change in forest cover in the past few decades. Source: Global Biodiversity Outlook 2 (2006). Click for full-size image.


However, global statistics tend to obscure significant differences in forest cover change among regions and countries. Net deforestation rates were highest in West Africa and South America. This was followed by Asia, particularly in South-East Asia, though it was significantly offset by forest plantation establishment in other parts of the continent.

In contrast, the forest cover in the other regions, largely in industrialized temperate countries, increased slightly primarily as a result of natural forest succession on abandoned agricultural land. The countries with the highest loss of forest area between 1990 and 2000 include Brazil, Indonesia, Sudan, Zambia, Mexico and the Democratic Republic of Congo. Those with the highest net gain of forest area during this period were China, USA, Belarus, Kazakhstan and the Russian Federation.

Along with the physical coverage or quantity of forests, it is equally important to consider the quality of forests. Quantity of forests (i.e. forest area) alone is an inadequate indicator of the health of a forest ecosystem since much of the world's forests are highly fragmented and face considerable human pressure.

Although deforestation is widely recognised as a major conservation challenge, the related issue of habitat fragmentation receives comparatively less attention. As human pressures increase in both temperate and tropical forests, areas that were once continuously forested have become more fragmented. In the Brazilian Amazon alone, the area of forest that are fragmented or prone to edge effects is 150 per cent greater than the area that has actually been deforested (FAO, 2003).

Small fragments have very different ecosystem characteristics from larger areas of forest, containing more light-loving species, more trees with wind- or water-dispersed seeds or fruits, and relatively few under-storey species. The smaller fragments also have more fallen trees, a more irregular canopy, more weedy species and unusually abundant vines, lianas and bamboos. Thus, they preserve only a highly biased subset of the original flora and fauna, which is adapted to these conditions.

In a 1997 study, the World Resources Institute coined the term "frontier forests" to describe forested areas that are relatively undisturbed by human activity and are large enough to maintain their original biodiversity, including viable populations of wide-ranging species.

According to this study, frontier forests constitute about 40 per cent of total global forest area, but are heavily concentrated in only three large blocks - two areas of northern (boreal) forest (in Canada, Alaska, and Russia), and one relatively contiguous area of tropical forest spanning the northwestern Amazon Basin and Guyana Shield (in Brazil, Peru, Venezuela, and Colombia). Additional important outliers can still be found in Central Africa (Congo), and Papua New Guinea. However, nearly 40 per cent of these remaining frontier forests face a moderate to high threat of degradation or clearance.

MadagascarForest burnt for farming, Madagascar © John Newby/Still Pictures

The demise of frontier forests is a major reason for an alarming loss of biodiversity around the world. The term 'biodiversity,' short for 'biological diversity,' refers to the total variety of all living things on earth, including individual species and whole ecosystems (see "Saving species").

According to UNEP's Global Biodiversity Outlook 1 Report (2001), about 60 per cent, and possibly closer to 90 per cent, of all species are found in tropical moist forests. The IUCN Red List of Threatened Species indicates that the number of critically endangered species is increasing with habitat degradation being one of the biggest causes for loss of biodiversity.

The value of forests

Vast forests are essential to life itself. They absorb carbon dioxide (the main climate-altering gas in the atmosphere) and produce oxygen, anchor soils and prevent erosion, regulate water flow and protect watersheds, modify climate and cool the air, and provide a habitat for millions of species of plants and animals.

Medicinal plantsCollecting medicinal plants in Sarawak © Nigel Dickenson/Still Pictures

By providing water cycle regulation, soil conservation, and biodiversity, forests are vital to maintaining healthy ecosystems - on which humanity depends.

Water and soil.

Forests are important agents of evapotranspiration, the exchange of water vapour among trees, soils and the atmosphere.

The Amazon River Basin, for instance, derives half its annual precipitation from the process of evapotranspiration. The world's rainforests themselves help to produce anywhere from 50 to 95 per cent of the moisture they need to maintain ecosystem functions. Take away the trees and the intricately-linked system unravels into dust.

Forest root systems hold soils in place, preventing erosion. And forest litter from leaves, twigs and bark, decays into rich humus that nourishes plants and sub-soil life, binds soil particles, and acts as a natural sponge to store water.

Trees also hold agricultural terraces in place on steep slopes, provide windbreaks for crops and maintain sand dunes. A World Bank study found that the rate of soil loss was 10 times higher on forest lands where slash-and-burn shifting cultivation was practiced than in undisturbed forests.

Saving species.

Saving tropical forests from destruction is vital to preserving biodiversity. Tropical forests, both wet and dry, cover only 7 per cent of the earth's land surface but contain over half of all known species of plants and land animals in the world. For example, one hectare of Peruvian rainforest contains nearly 300 tree species compared with just 50 tree species in the whole of northern Europe.

Costa Rica, with just 52,000 square kilometres of land, contains 8,000 species of plants, while Britain, with nearly five times the land area, has fewer than 1,500 species. Peninsular Malaysia has 8,500 species of plants - over 3 per cent of the earth's total on less than 1 per cent of the earth's land surface. As tropical forests are destroyed, thousands of species are obliterated as well.

Pest control.

The benefits of forests go far beyond their boundaries. Close to one-third of the world's 9,000 species of birds spend at least part of their lives in tropical forests. Painted weevil used to pollinate oil palms © Ron Petocz/WWFIn the North America farmers and foresters depend on migratory birds, along with bats and insects, to pollinate crops, disperse seeds, and prey on pests. Mexican brown bats dine on a variety of insects that plague corn, cotton, and potato crops in the United States, saving farmers millions of dollars in damages, while reducing use of pesticides.

Carbon reservoirs.

The world's forests act as great reservoirs that store about 830 billion tons of carbon. Trees are an important component of the global carbon cycle, a geochemical process that helps to regulate the atmospheric concentration of carbon dioxide. Living trees soak up carbon dioxide, but when the trees are cut down they become a source of carbon. In the last decade, tropical deforestation has released large amounts of stored carbon - accounting for roughly one-quarter of the carbon dioxide emissions to the atmosphere from human activity.

Economic value.

Forests also provide more direct benefits to the world's economies, including wood-based commodities such as timber, fuelwood, and pulp for paper and packaging. They provide foods, medicines, spices, gums, resins, and oils. Forest products are used for everything from lumber for housing and furniture to books and myriad other paper products. Even in the Internet age the flow of information still depends on paper.


Many spices come from the forest © Sophie Boussahba/Still Pictures



Forest products, mainly timber, pulp and paper, and fuelwood, are worth about $400 billion to the global economy. Non-wood forest products, such as fruits, vegetables and medicines, provide up to $20 billion a year and are growing rapidly in importance.

Calculations of the total worth of forests suggest far higher values. For example, a 1997 estimate by Robert Costanza of the University of Maryland is that the annual value of forest ecosystem services is $4.7 trillion - close to 15 per cent of the world's total GNP. But now these riches are under threat.

Population growth.

The relationship between population growth and deforestation has been a controversial issue. There are examples in both developed and developing countries where population increase has been accompanied by increasing tree cover.

There are also many examples, particularly where fuelwood and agricultural land is in much demand, of population growth and density resulting in increased pressure on forests.

More generally, it has been argued that it is no coincidence that 75 per cent of the loss of global forest cover took place in the 20th century, a century that saw 75 per cent of the historical growth in world population.

"The correlation makes sense," reasons Earth Policy Institute president Lester Brown, "given the additional need for farmland, pastureland, and forest products as human numbers expand".

Throughout the 1990s many countries with high rates of deforestation also had rapid population growth. In 1995 close to 1.7 billion people lived in 40 forest-scarce countries - those with less than one-tenth of a hectare of forest cover per capita. By 2025 4.6 billion people will live in forest-scarce countries. By then watersheds in China, Nepal, Thailand, and Vietnam are projected to be critically degraded as a result of the loss of forest cover.

Impact of consumption

At the same time, rapid growth in per capita consumption of forest products shares responsibility for destroying much of the world's frontier forests. Since 1960, for example, the use of paper and paperboard per person has nearly tripled.

The developed world accounts for most of the demand for forest products. Just 16 per cent of the world's population, based in North America, Europe and Japan consumes two-thirds of the world's paper and paperboard and half its industrial wood. Collecting fuelwood

Collecting fuelwood, Nepal © Jorgen Schytte/Still Pictures

But demand for fuelwood in developing countries also is expected to continue increasing along with demand for industrial wood.

Better management

FSC logoWith both population and per capita consumption increasing, it is becoming crucial for countries to manage their forest resources on a sustainable basis. Already, the current demand for forest products may exceed the limits of sustainable consumption by 25 per cent. A number of developments offer some encouragement, however, including the certifiction of forest products which are produced in sustainable ways.

These are gaining momentum.

People & the Planet would like to thank the IUCN Forest Conservation Programme and Population Action International's Population and Environment Programme for their contribution to this Overview.

See also Shrinking Forests: the many costs by Lester R.Brown