Chapter II. Biological and Ecological Context

A. Geographic overview

The scope of this review includes the countries of Burundi, Cameroon, the Central African Republic, Equatorial Guinea, Gabon, the Democratic Republic of Congo, Republic of Congo, and Rwanda. It also includes the border regions with Nigeria, Chad, Sudan, Uganda, Zambia, and Angola. The region under review straddles the equator, between approximately latitude 14 degrees north and south, extending between longitude 8 degrees and 32 degrees east. To simplify the compilation and presentation of background information, the report focuses on the eight nations wholly encompassed within this region (Map 1).

1. Climate

The countries of Central Africa constitute an almost exclusively humid or sub-humid enclave within a predominantly dry continent. This has not always been true. Central Africa has seen wide variations in rainfall in the past 100,000 years (Nicholson 1989), with some periods considerably wetter than today and others considerably drier. As Europe glaciated and deglaciated, air temperatures in Central Africa fluctuated. For much of the time between 20,000 and 70,000 years ago, temperatures in Central Africa were 4°C–6°C lower than at present; evaporation was consequently lower, and rainfall as much as 30 percent less than today (Bonnefille et al. 1990). The moist forest area was consequently diminished. Conversely, warmer periods associated with deglaciation in Europe resulted in increased rainfall and the recolonization of forest over Central Africa (Hamilton 1983).

Variations in climate have continued during the past 3,000 years, but they have not been of the same magnitude as observed over a more distant time scale. Africa was significantly more humid between the 10th and 13th centuries, when caravans traversed the desert along routes that are today impossible for lack of water. These conditions recurred during the 16th through 18th centuries, with the exception of several periods of severe drought in the 1680s, 1740s, and 1750s. At the end of the 18th century, marked desiccation commenced over much of Africa, and the decline in rainfall culminated in a period of severe drought in the 1820s and 1830s (all references Nicholson 1989). These historic droughts are analogous to those occurring today in the Sahel. Rains returned to produce a relatively humid period that persisted from the 1870s to the 1890s, and rainfall has continued to fluctuate to the present day. The unusually wet period between the 1950s and early 1970s may in fact have prompted the newly independent African nations to be overly optimistic in regard to agricultural production, resulting in the settlement and cultivation of areas that, while green at the time, had much lower long-term average rainfall prospects (Wilkie et al. 1999).

In Central Africa today, yearly mean temperatures vary little, averaging around 25°C. Annual rainfall in the region averages between 1,000 and 2,000 millimeters (Tchatat 1999). Most rain falls as convective showers in sporadic, localized rainstorms. Areas outside the tropical forest ecosystem, such as in northern Cameroon, northern Central African Republic, southern Democratic Republic of Congo, eastern Rwanda and Burundi, and the bordering zones in Chad, Sudan, Uganda, Zambia and Angola receive less rainfall, while the areas around Mount Cameroon and on the southern edge of insular Equatorial Guinea receive as much as 10,000 millimeters annually as a result of the combined effects of orography and the Benguela current. Throughout the region, rainfall is generally sufficient for there to be a positive water balance (i.e., precipitation exceeds evapotranspiration) during most of the year (Map 2; Figure 1).

The most striking aspect of rainfall within Central Africa is the source of the water vapor that leads to the convective precipitation characteristic of the region. Although the South Atlantic Ocean provides considerable water vapor to the hydrological system, 75–95 percent of the rainfall is from recycled water generated by evapotranspiration within the region (Balek 1977; Brinkman 1983). The importance of this so-called “small hydrological cycle” is much greater than it is in the Amazon Basin, for example, where it is estimated that about 50 percent of precipitation comes from terrestrial evapotranspiration (Salati 1987). In Southeast Asia, more than 80 percent of precipitation is not recycled but returns to the oceans as runoff (Brinkman 1983).

No data are available on the role of Central Africa’s moist forested regions and the extent to which they contribute to extra-regional precipitation. It is probable that the region is mostly a closed system in regard to rainfall, with some areas, such as the highlands of eastern Democratic Republic of Congo, receiving a somewhat larger proportion of the “small” hydrologic cycle rainfall as a result of orographic cloud formation.

2. Topography

Apart from Burundi, Rwanda, southwestern Cameroon, and eastern Democratic Republic of Congo, which are characterized by montane landscapes, the region is dominated by relatively flat terrain of between 300 meters and 600 meters above sea level (Map 3).

The highest peaks in the region include the following:

• The Ruwenzori mountains range (5,109 m), shared between the Democratic Republic of Congo and Uganda.
• The network of volcanoes in the east of the Congo Basin that are shared between the Democratic Republic of Congo, Rwanda, and Uganda. These include:

  • Kalisimbi (4,507 m), Muhabura (4,127 m), and Bisoke (3,711 m) in Rwanda;
  • Gahinga (3,473 m), shared between Rwanda and Uganda;
  • Sabyinyo (3,674 m), shared between the Democratic Republic of Congo, Rwanda, and Uganda; and
  • Nyamulagira (3,055 m), Mikeno (4,000 m), and Nyiragongo (3,470 m) in the Democratic Republic of Congo.

• Mount Cameroon (4,070 m) in southwestern Cameroon, within the coastal zone near the border with Nigeria.
• Peak Basile (3,008 m) in Equatorial Guinea, on the island of Bioko.
• The Nyungwe–Kibira mountain forest range, shared between Rwanda and Burundi. Some peaks in the range exceed 3,000 meters.

B. Ecoregions and land cover

The Central African region contains the largest remaining contiguous moist tropical forest in Africa, and the second-largest in the world after the Amazon. The region’s forests cover about 2.8 million square kilometers, approximately 70 percent of which is dense forest of more than 60 percent canopy closure (Map 4). The country with the highest forest cover rate, of about 85 percent, is Gabon. Burundi, with forest cover of less than 5 percent of country area, has the lowest rate of cover (Table 1).

Source: Adapted from Mayaux et al. (1997).

Central African ecosystems are biologically diverse and support a wide variety of vegetation types—notably evergreen rainforests, deciduous semi-moist forests and woodlands, montane forests and moorlands, inundated or swamp forests, forest clearings or “bais,” peat bogs, mangroves, rivers, and lakes (Map 5 and Figure 2).

Montane systems: A special case

Montane ecosystems tend to be biologically rich, because within relatively small areas, changes in rainfall, temperature, and insolation associated with an altitudinal gradient result in the formation of a great variety of habitats and ecological niches. The mountainous regions of Cameroon and the highlands bordering the Albertine Rift in the east of the Democratic Republic of Congo and in Burundi, Rwanda, and Uganda all reflect the high habitat richness typical of montane systems (Map 6). Though relatively low in taxonomic diversity compared to most lowland humid forests, these ecosystems harbor an important number of endemic species, such as Podocarpus usambarensis (Wilson and Catsis 1990).

Montane landscapes in Central Africa are typically volcanic in origin. Soils are highly fertile, although prone to erosion and mass slippage because of high rainfall and steep slopes. The high agricultural productivity of montane landscapes is reflected in the fact that they support the highest human population densities in Central Africa. Not surprisingly, given the level of demand for land and natural resources, montane habitats and species are under intense pressure; unspoilt montane landscapes are now rare outside of the national parks, and are being encroached upon even within the parks.

Of all landscapes in Central Africa, the montane areas are most at risk of habitat and species loss and are most in need of conservation investments.

C. Distribution and extent of shared water resources

1. Rivers

Central African hydrology is dominated by the Congo River Basin, the largest drainage system in Africa (Balek 1977) and the second-largest in the world. The Congo River drainage area covers 3.6 million square kilometers (Balek 1983) and includes almost all of the Democratic Republic of Congo, all but the southwest corner of the Republic of Congo, south and central Central African Republic, and southeastern Cameroon. The Songa, Ntem, Benito, and Ogooué Rivers form a basin that drains southern Cameroon, Equatorial Guinea, and Gabon. The northern Central African Republic is drained by the Chari River that flows into Lake Chad. Northern Cameroon is drained by the Bénoué that flows into the Niger and by the Logone that flows north to Lake Chad (Map 7; Boxes 2 and 3).

Average river runoff in Africa amounts to 2.1 million million cubic meters (2.1 x 10¹²) per year, of which 50 percent is generated within the Congo Basin. A mere 3 percent of annual stream flow is drawn off for human use. Water balance (the ratio of precipitation to evapotranspiration) is positive throughout most of the year within the region. Water stress nonetheless occurs in all but a few locations in Central Africa at some time during the year, with its length and severity increasing with latitude, and is a fundamental reason why the total flora of Central Africa is less than that of other tropical forest ecosystems. The region’s floristic diversity is nonetheless comparable to that of other regions (Richards 1952).

2. Lakes

There are eight freshwater lakes that border two or more countries in Central Africa. Of these, only Lake Chad lies outside the eastern rift valley region (Table 2). Lakes Albert, Edward, Kivu, and Tanganyika all support large numbers of fish species and are particularly diverse in Cichlids.

In addition to the lakes above, there are four more transboundary lakes in Central Africa: Mweru (shared by the Democratic Republic of Congo and Zambia), Cyohoha and Rweru (both shared by Burundi and Rwanda), and Chad (Shared by Cameroon, Chad, Niger, and Nigeria).

D. Biodiversity richness

1. Terrestrial biodiversity

The Central African region accounts for more than 60 percent of Africa’s biodiversity and ranks first in Africa for many taxonomic groups in terms of species richness. The numbers of plant, mammal, and bird species found in a sampling of Central African countries are presented in Table 3.

Source: WCMC database on global biodiversity (2000).

Many national parks and reserves lie along borders within the Central African region. Some are refuges of plant and animal species and are critical centers of endemism. These include:

• Korup National Park in Cameroon, contiguous with the Cross River National Park in Nigeria;
• Mount Cameroon National Park in Cameroon, bordering Nigeria;
• Campo and Ma’an reserves in Cameroon, bordering the Estuario de Rio Ntem Reserve in Equatorial Guinea;
• Altos de Nsok Reserve in Equatorial Guinea, bordering unprotected forests in Gabon;
• Conkouati National Park in the Republic of Congo, bordering unprotected forests and coastal landscapes in Gabon;
• Minkebe National Park in Gabon, bordering unprotected forests in Cameroon and the Republic of Congo;
• Nki forest reserve in Cameroon, bordering unprotected forests in the Republic of Congo; and
• Lobéké and Mongokele forest reserves in Cameroon, bordering the Dzanga–Sangha special reserve in the Central African Republic and the Nouabale–Ndoki National Park in the Republic of Congo.

2. Marine, coastal, and freshwater biodiversity

The Central African region is bounded in the west by a long Atlantic coast, extending from Cameroon to the Democratic Republic of the Congo, and passing through Gabon, Equatorial Guinea, the Republic of Congo, and Angola (Cabinda). This coastal area is a key breeding zone for marine turtles: more than 100 kilometers of beach, stretching from Mayumba in Gabon to the River Noumbi in the Republic of Congo, has been identified as the second most important site for marine turtle nesting in the world (Fretey 1998). The coast also is seasonally important for whales.

Mangroves additionally cover approximately 400,000 hectares in Gabon and 270,000 hectares in Cameroon. Mangroves harbor endemic flora and fauna, and are important breeding grounds for both marine and freshwater species of crustaceans, mollusks, fish, and birds (Mbog 1999; Makaya 1999).

E. Transboundary wildlife movement in Central Africa

In the absence of physical barriers to wildlife movement and plant dispersion, all species have the potential to cross political and land-tenure borders. In Central Africa, cross-border movement is most important for animals such as elephant, hornbills, mandrills, parrots, turtles, and cetaceans, which roam widely in search of scarce resources. Most other species are either highly territorial or do not require a large area to secure sufficient food, shelter, and mates to survive and reproduce.

1. Elephant

Central Africa constitutes the largest expanse of forest elephant range on the continent, and may harbor as many or more elephant as any other region in Africa (Table 4). Cross-border movements of elephant are common between the Central African Republic and Cameroon, the Republic of Congo, the Democratic Republic of Congo, and Chad. Between 300 and 400 elephants additionally migrate between the Lake Chad region in Chad and Cameroon, spending most of their time in Cameroon (Tchamba et al. 1997).

Source: Said et al. (1995)

Barnes et al. (1999) confirmed the movements of elephant between the Democratic Republic of Congo, Rwanda, and Uganda, tracking their movement from the Democratic Republic of Congo into the Queen Elizabeth National Park in Uganda and into the Toro/Semliki range in Uganda. Many of the animals may have used Queen Elizabeth National Park in Uganda as a refuge during the recent war. From the air, groups of elephant have also been seen moving from Toro/Semliki into the Democratic Republic of Congo. It is furthermore possible that elephant from Virunga National Park in Rwanda cross into the Democratic Republic of Congo.

High densities of elephant have been recorded in the forests that straddle the borders of southeast Cameroon, southwest Central African Republic, northern Republic of Congo (Turkalo and Fay 1995), and along the borders between Gabon and Cameroon and Cameroon and Equatorial Guinea. Elephant are known to cross the Sangha River between Cameroon and the Central African Republic and the Ngoko river between Cameroon and the Republic of Congo, and cross-border movements have been observed in the trinational zone between Congo, the Central African Republic, and the Republic of Congo. Elephant have been observed crossing the Sangha from Congo to the Republic of Congo, and cross-border movements are common between Equatorial Guinea and Gabon and between Equatorial Guinea and Cameroon, at the Ntem river. Elephant are also known to move between Cameroon and Gabon border across the Ayina river.¹

2. Marine fish

The coastal countries from Nigeria to Angola are characterized by the fact that they must share fish stocks, as most stocks extend beyond the exclusive exploitation zones of individual countries—individual stocks of species such as the horse mackerel may in fact be shared by all coastal nations in this region. Almost all stocks of marine fish are considered by the Food and Agriculture Organization (FAO) to be fully exploited or overexploited (FAO 2000).

3. Turtles

Five species of marine turtles are known to occur in the Atlantic Ocean near the coasts of Cameroon, Gabon, the Republic of Congo, the Democratic Republic of Congo, and Equatorial Guinea. These are the Loggerhead (Caretta caretta), Atlantic Green (Chelonias mydas), Leatherback (Dermochelys coriacea), Hawksbill (Eretmochelys imbricata), and the Olive Ridley (Lepidochelys olivacea) (Castroviejo et al. 1994). The Green and Hawksbill turtles are listed species by the International Union for Conservation of Nature and Natural Resources (IUCN). All five species of turtle are protected under Cameroonian legislation.

Three of the five species—the Olive Ridley, Leatherback, and Green turtles—have been known to nest in Cameroon, along the sandy shoreline between Equatorial Guinea and the Wouri Estuary. Local residents disagree as to the peak breeding season, but it is generally thought to be November to January. Four species—the Atlantic Green, Leatherback, Hawksbill, and Olive Ridley—come ashore to lay their eggs on the southern coast of Bioko Island in Equatorial Guinea during the dry season, November to February.

Between Equatorial Guinea and Gabon lies the Bay of Corisco, an area of approximately 1,570 square kilometers that has been identified as a year-round foraging ground for the Atlantic Green turtle and the occasional Hawksbill, Leatherback, and Olive Ridley. All species suffer heavy exploitation from local fishermen who use special nets, harpoons, and underwater guns to capture them. Hundreds of turtles are sold every year in the markets of cities such as Libreville and Bata (Bellini et al. 2000).

While Hawksbill nesting has not been confirmed at the beaches around the Bay of Corisco, more extensive surveys are still needed. Confirmed Hawksbill nesting sites in the region include Pointe Pongara, Gabon; São Tomé and Príncipe (Castroviejo et al., 1994); southern Bioko Island, Equatorial Guinea (Butynski 1996); and the region of Gamba, Gabon (Bellini et al. 2000).

All marine turtles feed in quiet, low-energy areas—i.e., areas with gentler surf—but nest on high-energy beaches. Most follow long migratory routes between their feeding and breeding areas. It is thought that many Leatherback turtles follow a cyclical migratory route that goes north along the east coast of North America, east past Greenland and Iceland, and south past Britain, Ireland, and the Iberian peninsula to nesting sites in West and Central Africa, before turning west at the equator to head back to North America. A Hawksbill turtle tagged in Brazil within its feeding grounds in Fernando de Noronha was captured in Gabon (Bellini et al. 2000), having traveled 4,669 kilometers. Little is known about the feeding grounds and migratory routes for turtles that nest on the beaches of Equatorial Guinea, Cameroon and Gabon.

Sea turtles are subject to a wide variety of human influence, including the destruction of nesting beaches due to development; removal of eggs; the killing of juveniles and adults by incidental catch in shrimp trawls, in other nets, and on long lines; and death from pollution and collision with boats. Several potentially serious threats specifically affect the sea turtles in the Central African coastal area. Nest predation has not been well quantified but appears to be severe (Castroviejo et al. 1994). Humans, monitor lizards (Varanus sp.), and ghost crabs (Ocypode sp.) are all frequent predators of eggs. Some adult females are also taken by locals while nesting on the beaches. Another important, as yet unquantified threat is represented by demersal fisheries for shrimp, fish, and squid. It is unknown whether the trawler fleets use marine turtle excluder devices in their nets.

In Gabon and Equatorial Guinea, efforts are being made to increase awareness among fishermen of the importance of tag recoveries and to encourage them to turn tags over to researchers (Bellini et al. 2000). In addition, several small local projects, coordinated by PROTOMAC (Protection de Tortues Marines d’Afrique Centrale), have begun to implement sea turtle protection programs throughout the Gulf of Guinea. It is nonetheless recognized that conservation efforts in one region could be rendered useless by exploitation in another part of the range, and that only through the concerted efforts of all nations within the range of the turtle population can protection be fully effective (Bellini et al. 2000).

4. Migratory birds

European and Arctic migrants, particularly wading birds, visit the coasts, rivers, wetlands, and forests of Central Africa during the northern winter. Little information on numbers, spatial distribution, or threats is available.

About 177 bird species migrate to Africa during the European winter (Langrand 2000). Between 445 and 655 individuals of the species Sterna sandvicensis (Sandwich tern) are believed to reside in Gabon (Langrand 2000). European swallows (genus Hirundo) visit the Central Africa Republic during the European winter, and are often trapped and eaten by children using alate termites as bate (J. Marot, pers. comm.). At least one study of the long-range movements of hornbills has been undertaken, but to date (T. Smith, pers. comm.) no published information is available on the intraregional movements of birds such as hornbills and parrots.

5. Cetaceans

A range of whales, including humpback, right, sperm, fin, sei, orca, and dolphins, visits the waters off the coast of the Republic of Congo, Equatorial Guinea, Gabon, and Cameroon, but little is known about their spatial distribution, movement patterns, or behavior.

F. Parks and reserves in border areas

Established in 1925 as the Albert National Park (809,000 hectares), the Virunga National Park was the first protected area in Central Africa. More than 300,000 square kilometers of national lands are now formally gazetted as parks or reserves, of which more than 50 percent abut international borders (Table 5; Map 8).

Though established ad hoc, the protected area network is surprisingly representative of the range of distinctive ecoregions (as defined by WWF–US) within Central Africa (Table 6).

Impact of armed conflicts on the management of border protected areas

Armed conflicts are increasingly degrading border protected areas and have often led to the suspension of management activities and a consequent decline in wildlife numbers. The lion (Panthera leo) has disappeared from the Akagera National Park in Rwanda as a result of the recent war, for example (Habiyambere 1999). The Virunga National Park in the Democratic Republic of Congo, the Volcanoes National Park in Rwanda, and the Kibira National Park in Burundi have all been degraded by refugee settlements and by the subsistence activities of refugees, such as firewood collection, hunting, and the collection of building material.

Mountain gorillas living in the contiguous landscape of the Volcanoes National Park, Virunga, and the Bwindi and Mgahinga National Park (Uganda) have all been affected by poaching, facilitated by the collapse of law enforcement and the emergence of armed militias during the civil wars there. Given this situation, it is remarkable that between 1992 and 1997 only 17 of the 620 extant mountain gorillas were killed (Table 7).

Source: Digit news (1998).

1. The author wishes to acknowledge Usongo, Nicanor, Mouncharou, De Watcher, Ndongo Allogho, and Huijbregts for the observations cited in this paragraph.