D

Deforestation

Over most of human history, the majority of thepopulationhas populated forested

portions of the planet. The forest vegetated realms evolved in several climate types

(seeClimate) and they range from the tropical rainforests to the taiga (seeBiomes).

Deforestation is usually defined to mean the reduction of a forest’s canopy cover to

below 10 percent of an area.

Over the extreme arcs ofEarth’s history, areas have deforested because

continental drift has moved regions into climate types not supportive of forests.

So, too, ancient deforestations can be recognized as being caused by volcanic

eruptions and explosions and, more extensively, by basalt flows covering hundreds

of thousands of square kilometers. It is manifest that natural climate change causes

some deforestation. The cold of the Pleistocene Epoch caused equatorward shifts in

climate types, and forests died in places far from the actual continental ice sheets. In

Sumatra and Borneo, the Pleistocene lowering of sea level by many tens of meters

caused shallow seas to disappear to create a large peninsula connected to the Asian

mainland and this peninsula became heavily forested. The rise of sea level after the

Pleistocene flooded and deforested the area and it became sea bottom again. Thus,

deforestation was ongoing far before the times dominated by humans.

Humans have become inexorably intertwined with deforestation. With today’s

rapid increase in world population, deforestation is of increasing concern. Earth

is losing forest at the estimated rate of 24 hectares (60 acres)per minute.Geo-

graphically, there are significant differences in deforestation. South America has

the greatest amount of deforestation per year while Africa has the greatest rate.

Brazil and Indonesia have the greatest total loss of forest while the central African

country of Burundi has had recent deforestation estimated at about 9 percent per

year. In some developed places such as the United States and the European Union

there have been increases in forest cover. However, this does little to staunch the

world trend. The largest remaining forested tracts are those associated with low

densities of human habitation and inaccessibility. They include the boreal

(northern) forests of Alaska, Canada, and Russia, and the remote tropical forests

of the northwestern Amazon basin and the eastern Congo basin.

Trees are large and obvious with their species and diversity emblematic of related

landscapeconditions. For humans, trees are useful. Humans use wood for fuel,

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