Congo-Brazzaville - Regions
The tropical rain forest that covers almost two-thirds of the country contains mostly coarse-grained soils with a fairly high sand and gravel content. Lateritic soils are widespread in low-lying areas and usually have been seriously leached. The soils of the evergreen rain forest produce little else but forest products and certain tree crops such as palm oil. The constantly high tempera¬tures and moist conditions foster the destruction of organic matter before it can be converted into valuable humus, and heavy rains wash away the topsoil. Under these conditions most soils tend to become poorer rather than richer with the passage of time.
In many of the savanna areas not adequately covered by vegeta¬tion, winds and rains combined to remove the best soils. These rich soils are often deposited along watercourses, and patches of fertile cropland are built up by this regenerative process. Mixed coarse and fine-grained soils are also extensive and are predominant in the plateau and hill regions. These soils drain slowly, and pools of standing water often remain for several days after periods of heavy rain.
The rain forest vegetation is always green because there is no dry season, and the extreme and heavy precipitation produces dense and luxurious growth. The broadleaf evergreen trees are closely spaced and provide a thick green dome that effectively keeps the sun from reaching the forest floor. There are numerous varieties and sizes of trees; many are gnarled, twisted, and vine-covered and others smooth, straight, and several hundred feet tall. Under the dense canopy, undergrowth is scarce, but where the canopy is occasionally broken, herbs, vines, and leafy plants grow in profusion.
In the swampy forest areas and along the coastal lowlands, stilt-rooted trees, such as the mangrove, emerge from the many lagoons. Other species of trees with buttressed root systems are also found in poorly drained depressions in the northeast. Marsh vegetation ii usually composed of reeds and grasses, which reach heights of three to five feet. In the areas of plateaus and rolling hills, open areas and parklike savanna growth are most common. The forest growth is mixed, and sizable patches of cropland are found among die scattered rolling plains.
Coastal Plain
The coastal area, lying to the southwest between Gabon and the exclave of Cabinda, is an undulating plain fringed with sandy shores. It stretches for about 100 miles along the south Atlantic coast and reaches inland approximately forty miles to the Mayombe escarpment to the northwest and to the foothills of the Crystal Mountains, which extend southeastward into the Congo from Gabon. The area is bisected by the Kouilou River, which drains the area between these two mountain ranges from Makabana to the sea.
The effect of the Benguela (Antarctic) Current flowing from the south is to enhance the formation of sandspits along the coastal plain, which is virtually treeless except in scattered areas. In addition to the mangrove-fringed lagoons, the area is marked by lakes and rivers with accompanying marshland and heavy vegetation in low-lying areas. Extensive swampy areas exist both to the northwest and southeast of the mouth of the Kouilou River.
Inland from the seacoast the land rises somewhat abruptly to a series of eroded hills and plateaus, which run parallel to the coastline. From the lower reaches of the Crystal Mountains on the Gabon border, this area rises southeasterly in a succession of sharp ridges of . the Mayombe range that reach elevations of 1,600 to 2,000 feet. Deep gorges have been cut in these ridges by the swift Kouilou River or its tributaries.
Niari Valley
Lying between the Chaillu Mountains to the north and the May-ombe Mountains to the south, the Niari Valley extends in a generally east-west direction for almost 200 miles. It varies considerably in width and contains more than 600,000 acres of the most fertile soil in the country. Originally covered with tall grasses and savanna, it has been extensively cleared to permit a great variety of agricultural pursuits and diversified industrial activity. Topographical conditions and the cooling effect of the Benguela Current account for a particularly favorable climate, which permits the harvesting of two crops per year.
While the northern slope of the valley rises somewhat abruptly to the Chaillu Mountains, the southern and eastern slopes increase more gently in elevation toward the treeless plains that form the Plateau of the Cataracts south of Brazzaville. Small streams and rivers afford good drainage for the valley floor, except in the northwest, where the joining of the Niari River with the Kouilou and the Louesse rivers permanently inundates much of the low-lying land south of Makabana. The valley contains the route of both the Congo-Ocean Railway and one of the main roads that connects Brazzaville with the port of Pointe-Noire, thus facilitating the transport of its products.
Central Highlands
The Central Highlands encompass the area generally known as the Bateke Plateau and extend for approximately 50,000 square miles over the south-central portion of the country. This region is characterized predominantly by rounded, low hills of less than 1,000 feet elevation and scattered rolling plains. In the northern part of this sector, however, toward the lower Gabon border, the hills are more peaked, and crests rise as high as 2,700 feet above sea level. For the most part the lower hills are untimbered and the plateaus grass covered.
The Central Highlands are not heavily settled and contain few roads and little industrial activity. The climate is tropical and in: eludes distinct wet and dry seasons. A considerable portion of the area north of the Niari River and extending as far west as the vicinity of Zanaga is covered with dense tropical forest. Subsistence agriculture is practiced, and only a limited amount of fertile cropland is available.
To the northwest along the Gabon border and running almost to the equator, a region of hills and plateaus forms the western rim of the Congo Basin. The plateaus are separated from each other by deep valleys that carry the eastward-flowing tributaries of the Congo River. Savanna and tropical rain forest are interspersed throughout the entire area. Transportation was limited, and the bulk of travel was performed on the navigable portions of the streams and rivers.
Congo Basin
The northeast section of the country, covering an area of approximately 60,000 square miles, lies within the Congo Basin. It consists of flat, swampy valleys and low divides descending east and southeast from the western hills to the Congo River. The region is covered with dense equatorial rain forest, and large portions lying northeast and southwest of the Sangha River are permanently inundated. Flooding occurs seasonally almost everywhere, and in areas south of Mossaka, along the Congo River, extensive marshland covered with swamp vegetation exists.
The rivers of the basin had been the primary communication routes between the interior and the population centers to the south, and the Oubangui and Congo rivers formed the principal trade artery for the entire region, as well as for countries immediately to the north. Aside from the production of palm oil, the principal economic activities of the region were limited to wood and wood products. Considerable portions of the Congo Basin were virtually uninhabited, and the sparse settlements that existed engaged in hunting, fishing, trading, and subsistence agriculture.
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