Forests of the Congo Basin

Africa, the second largest continent after Eurasia, contains over 20 percent of the world's remaining rain forest, the largest and least disturbed section of which lies within the Congo River drainage.

As the giant granitic block that became the African continent slowly warped and its edges uplifted, its equatorial center formed a broad, shallow bowl some 1,600 kilometers (1,000 miles) in diameter. By the Tertiary period (65 to 1.6 million years ago) this depression was a vast lake that, as a result of the inexorable forces of erosion, slowly drained through a narrow outlet to the Atlantic, exposing what is now the forested Congo basin.

The Congo basin covers some 3.6 million square kilometers (1.4 million square miles), an area a little less than half the size of the United States, and contains over 50 percent of Africa's tropical rain forests. It extends in a contiguous zone from Gabon on the Atlantic seaboard through the People's Republic of the Congo, Cameroon, Central African Republic, and Zaire. other sections of rain forest still remain in Nigeria, in areas west of the Dahomey Gap in the Ivory Coast and Guinea, and on the eastern edge of Madagascar.

Although rain forests are thought to be one of the oldest of all forests, having remained unchanged for millennia, recent pollen studies clearly show that much of the area now covered by tropical rain forest in Africa is, in geological time, of very recent origin. When Europe and North America were under miles of glacial ice, tropical Africa's annual temperature and rainfall were less than they are today, and the Congo basin forests shrank in size until only three remnant patches of forest existed. These Pleistocene refugia sustained and preserved the plants and animals that depend on a constant hot (27 degrees Celsius or 80 degrees Fahrenheit), humid (80 percent), rain-drenched (1,800 millimeters or 72 inches per year) environment and are now unique to Africa's rain forests. As the last ice age gradually receded rainfall increased, and the boundaries of the refuge forests in Guinea, Gabon, and eastern Zaire expanded to fill the vast central basin. That the central region of the Congo forest was recently (in a geological sense) savanna scrubland is reflected by its much lower variety of plants and animals compared to the Pleistocene refuge areas such as the Ituri forest of northeastern Zaire.

The Ituri was the largest and most ecologically diverse of the three Pleistocene refuges and consequently now contains the greatest number of plant and animal species of any African forest, over 15 percent of them endemic to that area. The forests of the Congo basin now appear to be at equilibrium with the environment and are neither exhibiting a natural expansion nor contraction of their domain.