Biological diversity in the coastal forests of Eastern Africa

Published: August 26, 2008, 6:37 pm

Topics:

Biodiversity (main) Ecology (main)

Overview The lattice of roots of mangrove forests serve to stabilize coastal areas and act as nursery areas for fish; however, demand for building poles and fuel wood has degraded many areas of mangroves. (© John Watkin) The Coastal Forests of Eastern Africa is a biodiversity hotspot (Biological diversity in the coastal forests of Eastern Africa) identified by Conservation International, and stretches along the eastern edge of Africa, from small patches of coastal (riverine) forest along the Jubba and Shabelle Rivers in southern Somalia, south through Kenya, where it occurs in a relatively narrow coastal strip of about 40 kilometers in width, except along the Tana River where it extends about 120 km inland. The hotspot stretches farther south into Tanzania (where some outlying forest patches occur about 300 km inland), and along nearly the entire coast of Mozambique, ending at the Limpopo River (south of which is the Maputaland-Pondoland-Albany Hotspot). The hotspot also includes the offshore islands, including Pemba, Zanzibar, Mafia and the Bazarruto Archipelago off Mozambique. The hotspot's vegetation is a complex mix of moist forests and dry forests, with coastal thicket, fire-climax savanna woodlands, seasonal and permanent swamps, and littoral habitats that include mangrove vegetation along some parts of the coast. Trees dominate the coastal flora, but lianas are also common as are shrubs, herbs, grasses, sedges, ferns, and epiphytes. Coastal forests are found up to 500 meters above sea level, although in Tanzania they occur up to 1,030 meters on Handeni Hill, though this is unusual.

The climate is largely tropical, though some of the southern areas are almost subtropical. The hotspot has high temperatures and high humidity. There are two rainy seasons (long, April-June; short, November-December) in the north, becoming one rainy season (November-April) in the south. Rainfall ranges from about 2,000 millimeters/year on Pemba and Mafia down to about 500 millimeters/year in northern Kenya, although average rainfall in most of the coastal forests is between 900 and 1,400 millimeters/year.

Unique and Threatened Biodiversity

Kirk's red colobus monkey (Procolobus kirkii, EN) is endemic to the island of Zanzibar, off the coast of Tanzania. The total population of this species ranges between 1,000 and 1,500 individuals. (© Patricio Robles Gil/Sierra Madre)

Although the remaining forests scattered throughout the hotspot's 291,250 km² are typically tiny and fragmented, they contain remarkable levels of biodiversity. These forests also vary greatly in their species composition, particularly among less mobile species; for example, forests that are only 100 kilometers apart may differ in 80 percent of their plant species.

Within the hotspot, the region of highest endemism stretches from northern Kenya to southern Tanzania, possibly also including northernmost Mozambique. Two important subcenters of endemism are also recognized: the Kwale-Usambara subcenter of endemism on the Kenya-Tanzania border, and the Lindi subcenter of endemism in southern Tanzania.

Plants

There are about 4,050 vascular plant species in the Coastal Forests of Eastern Africa Hotspot and approximately 1,750 (43 percent) of the plant species are endemic. The hotspot holds at least 28 endemic plant genera, most of which are monotypic. About 70 percent of endemic species and 90 percent of endemic genera are found in forest habitats. Furthermore, about 40 percent of the endemic plant species are found in only a single forest; for example, the Rondo Forest in southern Tanzania has about 60 endemic species and two endemic genera.

Among the best-known plants in the hotspot are the species of African violets (Saintpaulia spp.). The 40,000 cultivated varieties of the African violet, which form the basis of a US$100 million/year house plant trade globally, are all derived from just three species found in coastal Tanzanian and Kenyan forests. The hotspot also contains 11 species of wild coffee, eight of which are endemic; none of these species has been exploited commercially.

Vertebrates

Birds

More than 633 bird species occur in the hotspot; eleven of these are endemic. Pemba Island, which is one of BirdLife International's Endemic Bird Areas, has four endemic species: the Pemba white-eye (Zosterops vaughani), Pemba green-pigeon (Treron pembaensis), Pemba sunbird (Nectarinia pembae), and Pemba scops-owl (Otus pembaensis). The Tana River cisticola (Cisticola restrictus) is endemic to the Lower Tana River, and the Malindi pipit (Anthus melindae) is endemic to the coastal grasslands of Kenya. Most of the other endemics are found in the mainland coastal forest of Kenya and Tanzania, including the yellow flycatcher (Erythrocercus holochlorus), Sokoke pipit (Anthus sokokensis, EN), Clarke's weaver (Ploceus golandi, EN), and Mombasa woodpecker (Campethera mombassica).

Mammals

The golden-rumped elephant shrew or sengi (Rhynchocyon chrysopygus, EN) is endemic to the coastal forests Kenya north of Mombasa. (© G. Rathburn)

Nearly 200 mammals are found in the Coastal Forests of Eastern Africa hotspot, and 11 of these are endemic, including the Ader's duiker (Cephalophus adersi, EN) from Zanzibar, Arabuko-Sokoke Forest and Boni-Dodori Forest, the Pemba flying fox (Pteropus voeltzkowi, VU) restricted to Pemba Island, the Kenyan wattled bat (Glauconycteris kenyacola), the Dar es Salaam pipistrelle (Pipistrellus permixtus), the golden-rumped elephant shrew (Rhynchocyon chrysopygus, EN), occurring in a narrow coastal strip in southeastern Kenya, and a recently described species of horseshoe bat (Rhinolophus maendeleo) in the Amboni Caves in Tanga District in Tanzania.

The stark contrast between the area within the Mwaluganje Elephant Sanctuary and the surrounding landscape reflects the difference in land use practices, which need to be resolved to reduce human/wildlife conflict. (© John Watkin)

The primates are important flagship species for this hotspot. This relatively tiny hotspot boasts three endemic monkey species. Found only in small patches of gallery forest along the lower Tana River in Kenya, the Tana River red colobus (Procolobus rufomitratus, CR) is represented by only about 1,100-1,300 individuals, while the Tana River mangabey (Cercocebus galeritus, CR) has been reduced to only about 1,000-1,200 individuals. The Zanzibar red colobus (Procolobus kirkii, EN) has an estimated population of about 1,000-1,500 individuals, mainly in Zanzibar's Jozani Forest, but also in a number of village forests. The Zanzibar red colobus is a significant tourist attraction that, historically, was not hunted by the Muslim inhabitants of the Island; however, there have been recent reports that suggest it is being hunted by immigrants from the mainland. There are also two endemic species of galagos (out of a total of four occurring in the hotspot): the Rondo dwarf galago (Galagoides rondoensis) in the southern Tanzanian forests, the Kenya coast galago (G. cocos) from northern Tanzania and into Kenya.

The hotspot also still supports considerable populations of threatened large African herbivores, including black rhinoceros (Diceros bicornis, CR) and savannah elephants (Loxodonta africana, VU), especially in the larger protected areas and wilderness regions of southern Tanzania and northern Mozambique. There are also populations of African wild dog (Lycaon pictus, EN).

Reptiles

There are about 250 reptile species in the Coastal Forests of Eastern Africa Hotspot, and more than 50 of these are endemic. The hotspot has one endemic reptile genus, Scolecoseps, which is represented by three species.

Amphibians

The hotspot also has over 85 amphibian species, six of which are found nowhere else. These endemics include the Mafia Island toad (Stephopaedes howelli, EN), Shimba Hills banana frog (Afrixalus sylvaticus, EN), Shimba Hills reed frog (Hyperolius rubrovermiculatus, EN), and Phrynobatrachus pakenhami (EN), known only from northern Pemba, particularly Ngezi Forest Reserve. One species largely confined to the hotspot is Loveridge's snouted toad (Mertensophryne micranotis), the only member of its genus; this species is remarkable in that it is one of the few amphibians to breed by internal fertilization, although it still lays eggs, rather than giving birth to live young. In addition, a new genus of frog, similar to members of the genus Kassina, has recently been found in the Jozani Forest on Zanzibar and awaits description.

Freshwater Fishes

Nearly 220 fish species live in the fresh waterways of the Coastal Forests of Eastern Africa, and more than 30 of these are endemic. Of the 34 families represented in the hotspot, minnows (family Cyprinidae) are dominant, followed by killifishes (Nothobranchius spp.). Some species of fish have remarkable adaptations to survive in the hotspot's temporary coastal swamps and floodplains. For example, the air-breathing lungfishes Protopterus amphibious and P. annectens can survive in a dormant state for over a year in cocoons underneath dried mud.

Invertebrates

Levels of endemism within some invertebrate groups are significantly higher than among vertebrates. About 80 percent of millipedes and 68 percent of mollusks are found nowhere else. The hotspot is also home to a Gondwana relict dragonfly species (Coryphagrion grandis) that has its nearest relatives in Central and Southern America.

Human Impacts

Much of the hotspot's original forests have been lost to agricultural conversion and urbanization, and only about 10 percent of the original vegetation – 29,125 km² – remains in pristine condition. The remaining habitat is limited to more than 400 patches of lowland forest, covering about 6,259 km². The remaining forest covers about 2 km² along the Jubba River of Somalia, 787 km² in Kenya, 692 km² in Tanzania, and at least 4,778 km² in Mozambique.

Pictured is a gray morph of the Sokoke scops owl (Otus ireneae, EN) in the Arabuke-Sokoke Forest of Kenya. The owl is threatened due to habitat loss and fragmentation. (© John Watkin)

The most significant current threat to the Coastal Forests of Eastern Africa Hotspot is the expansion of agriculture. Because the soil is poor and can only support subsistence agriculture, most agricultural development involves short-term shifting cultivation concentrating on food crops such as cassava, maize, banana, pawpaw and coconut. The human population is increasing 2.5 - 3.5 percent annually, and the demand for additional farmland increases every year. Commercial agricultural development, in the form of coconut, sisal, clove, cardamom and cashew nut plantations, has also led to the loss of lowland coastal forests and other natural habitats.

Burning of woody plants for charcoal production causes major habitat loss near coastal towns and alongside main roads in Tanzania, while the collection of firewood poses a threat in areas away from towns and roads. Forests close to tourist areas, such as Arabuko-Sokoke Forest near Malindi and Watamu in Kenya, suffer from the high demand for carving wood (Brachylaena huillensis) and timber for the construction of hotels, private residences and tourist attractions. The carving wood industry is much bigger in Kenya than in Tanzania and poaching of carving wood trees is most common in Tanzania near the Kenya/Tanzania border. Uncontrolled burning to clear farmland, to drive animals for hunting, to collect honey, and to reduce tsetse flies also threatens lowland coastal forests and thicket patches, often replacing rare, endemic coastal forest species with more common wide-ranging fire-adapted species. Illegal logging using pit-sawing techniques is also a problem in almost all coastal forests where timber trees still remain, particularly in northern Mozambique and southern Tanzania.

In addition to important biological resources, the countries of eastern Africa are also endowed with a wealth of mineral resources; in coastal areas these include gas, gemstones, iron, titanium, limestone and kaolin. Destructive mining practices can destroy large areas of natural habitat. The coastal sands contain titanium and the mining of this ore destroys the natural vegetation. The Kenyan Government has recently given approval to a Canadian-based multinational mining company, Tiomin, Inc., to start mining titanium in the Kwale area. High-grade silica sands for glass manufacture are also mined from deposits in Msambweni, while iron and manganese are mined on a small scale in the Kwale Kaya forests of coastal Kenya. There are also extensive areas of limestone along the coast, and rubies and other precious stones in some of the coastal forests of Tanzania.

Conservation Action and Protected Areas

About 50,889 km² of the Coastal Forests of Eastern Africa Hotspot, 17 percent of the hotspot's land area, are under some form of protection. However, only 11,343 km² (4 percent) of the land area is conserved in protected areas in IUCN categories I to IV.

Pictured is a gray morph of the Sokoke scops owl (Otus ireneae, EN) in the Arabuke-Sokoke Forest of Kenya. The owl is threatened due to habitat loss and fragmentation. (© John Watkin)

The two largest protected coastal forests in Kenya are Arabuko-Sokoke Forest Reserve (417 km²) and the Shimba Hills National Reserve (63 km²). In Tanzania, there are no protected coastal forests larger than 40 km². Mozambique is home to some of the largest patches of remaining coastal forest, and the new Quirimbas National Park may contain larger areas of coastal forest than Arabuko-Sokoke.

The management effectiveness of the protected areas varies widely across the hotspot. In Kenyan portion of the hotspot there is a single National Park, a six square kilometer area northwest of Arabuko-Sokoke, but it contains no closed forest and exists on paper only. While four National Reserves fall under the jurisdiction of the Kenyan Wildlife Service, most of the other Kenyan forests are within Forest Reserves, which are managed for a variety of forest products. Nearly 40 percent of Kenyan coastal forests are either poorly protected Local Government or County Council Forests, or otherwise wholly unprotected.

In Tanzania, most of the closed forests are within Forest Reserves under central government control, with a few local-authority Forest Reserves under district control. Most of the other forests are unprotected and found on Village or General Land. The new Sadaani National Park incorporates two coastal forests sites, Zaraninge and the former Mkwaja ranch. The Selous Game Reserve includes some forest and thicket patches, as do the terrestrial portions of Mafia Island and Dar es Salaam Marine Parks. The coastal forests close to Dar es Salaam face the biggest conservation challenges, from incursion for charcoal burning, fuelwood harvesting, agriculture and logging.

In Mozambique, conservation has become a higher priority since the cessation of civil war in 1992 and a period of reconstruction. Quirimbas National Park, declared in 2002, includes coastal forest habitat, as well as marine areas and extensive miombo woodlands. In 2003, a large Ramsar site was declared within the Zambezi Delta.

A number of NGOs have been working in this region. In Kenya, BirdLife International and Nature Kenya have worked toward the conservation of Arabuko-Sokoke for more than 10 years, and WWF has provided assistance to the conservation of the Kaya Forests. In Tanzania, WWF, the Wildlife Conservation Society of Tanzania, the Tanzania Forest Conservation Group, CARE-Tanzania, and the IUCN forest program are working to conserve important coastal forests. In both Kenya and Tanzania, there has been a movement toward Participatory Forest Management, engaging the rural population in the conservation process in the hope that an exchange of forest user rights for community management responsibilities and sometimes ownership will lead to better protection.

Over the past couple of years, a program coordinated by WWF has brought together representatives from Kenya, Tanzania and Mozambique to develop a common vision for the way forward for conservation of the coastal forests. National coastal forest task forces have also helped develop an ecoregion-wide approach to conserving these forests. In addition, recent data gathering, funded by the Critical Ecosystem Partnership Fund, has further refined conservation priorities in the hotspot allowing the identification of 112 Key Biodiversity Areas along the Kenyan and Tanzanian coastal forests, to build from the Important Bird Areas already identified by Nature Kenya and the Wildlife Conservation Society of Tanzania as site-scale conservation targets for the hotspot.

Notes This article is based on contributions from Neil Burgess, Ian Gordon, John Salehe, Peter Sumbi, Nike Doggart, Alan Rodgers, and G. Philip Clark.For a complete list of all contributors to the Biodiversity Hotspot program, see Biodiversity Hotspot Site Credits (Biological diversity in the coastal forests of Eastern Africa) .

Further Reading

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• Bearder, S. K. 1999. Physical and social diversity among nocturnal primates: A new view based on long term research. Primates 40: 267-282.
• Bearder, S.K., Ambrose, L., Harcourt, C., Honess, P.,Perkin, A., Pimley, E., Pullen, S. & Svoboda, N. 2003. Species-typical patterns of infant contact, sleeping site use and social cohesion among noctural primates in Africa. Folia Primatol 74: 337-354.
• Broadley, D. Undated. The Reptiles of the East African Coastal Mosaic. BFA Seminar Series no. 19. Bulawayo, Zimbabwe: Biodiversity Foundation for Africa.
• Burgess, N.D. & Muir, C. (Eds.). 1994. Coastal Forests of Eastern Africa: Biodiversity and Conservation. Proceedings of a workshop held at the University of Dar es Salaam, August 9-11, 1993. Society for Environmental Exploration/ Royal Society for the Protection of Birds, UK.
• Burgess, N.D., Clarke, G.P. & Rodgers, W.A. 1998. Coastal forests of eastern Africa: Status, species endemism and its possible causes. Biological Journal of the Linnean Society 64: 337â??367.
• Burgess, N.D., Kock, D., Cockle, A., FitzGibbon, C., Jenkins, P. & Honess, P. 2000. Mammals. In N.D. Burgess & G.P.Clarke. The Coastal Forests of Eastern Africa. pp. 173-190. Cambridge: IUCN Forest Conservation Programme.
• Burgess, N.D. & Hipkiss, A. 2002. Pande Game Reserve: Observations on forest loss between July 1989 and November 2001. The Arc Journal 14: 1-3.
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Citation

International, C. (2008). Biological diversity in the coastal forests of Eastern Africa. Retrieved from http://editors.eol.org/eoearth/wiki/Biological_diversity_in_the_coastal_forests_of_Eastern_Africa