ANTHROPOLOGISTS believe that species ancestral to ours lived amid the trees, later emerging to grassland savannas to explore and hunt.

Still cradles of life, forests also perform all kinds of practical services that benefit modern humans. They produce oxygen we breathe and suck up air pollution.

In the United States, 80 per cent of fresh water originates in forested areas. Forests purify water and refill underground aquifers; in addition, they absorb rain, and slow down floods and water runoff.

Forests and woodlands over the world have changes over the millenia due to changes in climate and geology. In the modern world, forests are classified into various groups, including temperate-zone and tropical forests. Not all rain forests are in the tropics — some are in cooler climates. And there are other kinds, such as riparian forests, that separate interior areas from coastlines.

Each part of the forest supports life. The soil is full of uncounted numbers of microbes, insects and fungi, essential to recycling organic matter, and thus to the survival of all life on earth.

Larger animals live on the forest floor, and the shrub and tree canopy layers are vital to birds. There are about 1.5 million known species in the world, and the true number of species may be 10 times more than that. Many of these spend their lives growing, burrowing, wriggling, or plodding along in forests — or flying through trees.

The extent of forested lands has made it possible for birds and animals to range freely in search of food and appropriate climate; the resulting horizontal and vertical complexity of the forest and its density of life creates biodiversity.

Tropical forests generate the richest biodiversity, as the energy generated by the equatorial sun encourages life to proliferate amid abundant nutrients.

Unfortunately, these forests are quite fragile, and over the past half-century have succumbed in large numbers to human clearing and logging. Global forests themselves, as well as diverse reserves of plants and animals, are threatened as never before.

It has been estimated that by the late 1980s three quarters of old-growth forests on the planet had been destroyed, including about half of tropical and temperate rain forests; and human population expansion continues to the clearing of new lands.

According to the US State Department, “one of every six known bird species, one of every 11 mammals, and one of every 15 reptiles” makes the Amazon rain forest its home. Unfortunately, as David B Sandalow, assistant secretary of state for oceans and international environmental and scientific affairs, recently noted:

“Tropical forests are disappearing at an alarming rate. Saws and bulldozers are levelling roughly 200 hectares per minute. A soccer field is close to two hectares, so we are losing about 120 soccer fields of tropical forest per minute, more than 7,000 soccer fields per hour, more than 170,000 soccer fields per day.’

Around the globe, forests that are not totally destroyed are being fragmented by roads and human development, a change that threatens the health and survival of indigenous plants and animals. Biologists believe that destroying 90 per cent of a wooded habitat reduces local species by about a half.

It is estimated that 500 million people around the world, depend on forests for their livelihood — an incentive to preserve the health of forests and to protect them as a sustainable resource for future generations.

— Excerpts taken from “Biodiversity On a Changing Planet”, published by the Office of International Information Programs, US Department of State.