Ecoregions

Comoros forests

August 7, 2012, 8:40 pm
Content Cover Image

Comoros Islands Photograph by William Trewhella

The Cormoros forests are situated on the four Comoros Islands, which are distinctive in size, shape, and topography, with a variety of habitat types. The two larger islands, Grande Comoro and Anjouan have significant topographic relief and support lowland and montane rainforests. Mangrove habitats are present along the coasts and areas of sparse herbaceous vegetation exist on Grande Comore where lava flows have left little soil. The flora and fauna has biogeographical affinities to Madagascar and to a lesser degree to the African continent. Like many Indo-Pacific islands, the Comoros host a diverse array of endemic species, including more than 500 species of plants, 21 species of birds, nine species of reptiles, and two species of fruit bats. However, forest cover is rapidly declining and less than 30 percent of the original area is left today; many of the endemic species are severely threatened from habitat loss and invasive species, and others have already gone extinct. Frequent cyclones and volcanic activity pose further risks to the surviving species. Conservation of the remaining forested areas, particularly on Mount Karthala on Grande Comore, Mount Ntringui on Anjouan, and Mount Koukoule on Moheli, is a priority for the conservation of endemic species.

Location and General Description


 

This ecoregion covers the forests and former forested habitats of the Comoros Islands in the western Indian Ocean. These islands are located in the northern part of the Mozambique Channel about 300 kilometers (km) from northern Madagascar and about 300 km from the mainland of East Africa. There are four islands in total - Grande Comore (1,146 km2), Moheli (211 km2), and Anjouan (424 km2) comprise the Independent Republic of the Comoros, and Mayotte (374 km2) is a French dependent territory.

The Comoros islands have a maritime tropical climate. The rainy season is from October to April when the predominant northerly winds of the Indian Ocean bring moist, warm air to the region. The average temperature during the wet season is 25 °C with temperatures reaching above 29 °C in March, the hottest month. From May to September southerly winds dominate the region bringing cooler (approximately 18 °C) and drier air. Rainfall and temperature vary from island to island throughout the year and even vary within islands due to the dramatic topography. The central, higher elevation areas of an island are often cooler and wetter than the coastal regions. This climatic variation results in distinct microhabitats/microecosystems on the islands with correspondingly distinct flora and fauna.

The Comoros Islands are purely volcanic in origin, ranging in age from the oldest, Mayotte, to the youngest island, Grande Comoro. Grande Comoro is dominated by the still active volcano Mount Karthala (2,355 meters (m)), which erupts every 10 to 20 years. The 1977 outpourings of basaltic lava from this mountain are already being colonized by vegetation. However, the forests as well as the soils developed over these volcanic materials are immature. Stuart et al. reported that 7 percent of the island’s surface is in pasture, 16 percent remains as native forest and woodlands, and only 43 percent of the island’s surface is cultivatable, although this figure may be low, since cultivation on Anjouan occurs on slopes greater than 60 degrees. The majority of the natural forest vegetation has been cleared, and this clearance is still proceeding. Because the soil on these islands consists of laterite, which is rich in minerals but very poor in humus material, it is subject to extreme erosion when forest cover is removed.

With some exceptions the vegetation in this ecoregion is similar to that on Madagascar. The lowland and mid-elevation evergreen moist forests are the largest and most threatened habitat, occurring from sea level to approximately 1800 m in elevation. Above 1800 m on Mount Karthala, stands of a giant heath (Phillipia comorensis) dominate the rugged landscape. Sparse herbaceous vegetation grows on lava flows and cinder fields at the base of this active volcano. Other lowland areas host a characteristic Indo-Pacific scrub formation. There are at least 935 plant species registered on these islands, of which over 40 percent or 416 are native. Major plant families include Sapotaceae, Ebenaceae, Rubiaceae, Myrtaceae, Clusiaceae, Lauraceae, Burseraceae, Euphorbiaceae, Sterculiaceae, Pittoscoraceae, and Celastracea.

Biodiversity Features

Of the approximately 2000 native plant species, including 175 ferns and 72 species of orchids, 33 percent are endemic to the Comoros. Most of the flora of these islands has affinities with those of Africa and Madagascar; however, a small percentage is more closely related to that of Asia.

The species richness of the fauna is relatively low on the Comoros, although it is higher than most other Indian Ocean Islands due to its proximity to both Madagascar and continental Africa. There are only 8 species of extant native terrestrial mammals include three species of fruit bats, 3 insectivorous bat species and two lemurs. There are 25 species of terrestrial reptiles and two species of sea turtle, including green turtle (Chelonia mydas) that nest on the beaches of these islands, and hawksbill turtles (Eretmochelys imbricata), which are seen in the waters around the islands. Species diversity in birds and amphibians is also rather low.

Although the animal species richness is relatively low on the Comoros, there is a high proportion of endemic species. Among the avifauna, 21 species are considered strict endemics to this ecoregion. Twelve species are confined to just one island and the others occur on several of the islands. Examples include the Anjouan sunbird (Nectarinia comorensis) and the Anjouan brush-warbler (Nesillas longicaudata) that are strictly confined to Anjouan Island, and the Comoro olive-pigeon (Columba pollenii) and Comoro blue-pigeon (Alectroenas sganzini) which occur on all the islands. Most of these species are found in the diminishing lowland forest areas, and one, the Mount Karthala white-eye (Zosterops mouroniensis VU), is found only in the higher elevation heath vegetation zone (above 1,700 meters) of Mount Karthala, on Grande Comore. This mountain has four species of birds strictly confined to it, including the critically endangered Karthala scops owl (Otus pauliani), Grand Comoro flycatcher (Humblotia flavirostris, EN), and the Grand Comoro drongo (Dicrurus fuscipennis, EN), so all these species are extremely vulnerable to habitat loss. Several of the bird species have populations less than 100 individuals and are thus critically endangered. An additional two species of birds are regarded as threatened with extinction: the Mayotte drongo (Dicrurus waldenii, EN) and the Anjouan scops owl (Otus capnodes, CR).

Of the 8 native mammals present on these islands, two species of fruit bats are endemic (Pteropus livingstonii and Rousettus obliviosus). Other native mammals include the mongoose lemur (Eulemur mongoz, VU) and a near-endemic sub-species of fruit bat (Pteropus seychellensis comorensis). Of the 34 reptiles present, 9 are strict endemics. Endemics include two species of day geckos (Phelsuma spp.), four species of shinning-skink (Cryptoblepharus spp.), and two species of chameleon (Furcifer spp.). These are no species of endemic amphibian. Among the dozens of endemic Lepidopterans are two species of swallowtail butterflies, Papilio aristophontes and Graphium levassori.

Cyclones and volcanic activity are major ecological processes that affect biodiversity. Cyclones bring heavy winds, which can affect fruit bat populations, topple trees, and cause landslides. These effects are exacerbated by recent logging activities that open forest areas increasing their exposure to wind. Volcanic activity affects biodiversity by covering intact habitat. Recent lava fields host a number of unique plant species that are adapted to these dry and sun-exposed conditions.

Current Status

The conservation status of forests in this ecoregion is poor. The human population of the islands is high, with over 700,000 residents on the four islands combined (with a population density greater than 330 people/km2). Population growth hovers around 3 percent per year and is putting increasing pressure on the forests. Little good agricultural land remains because of the rugged topography on the three islands of the RFI Comores. The majority of the human population of Grande Comoro and Mayotte is concentrated in the coastal lowland areas. However, on Anjouan, and to a lesser extent Moheli, there are significant populations in mountain villages. Introduced exotic species are problematic on these and other islands, and several management programs have been enlisted to control and even eliminate some of them.

The native vegetation of all Indian Ocean islands is seriously endangered due to the extensive conversion of land to agricultural use. Lowland forests have been almost completely destroyed up to 300 or 400 meters on all four of these islands, making it likely that some endemic plant species are already extinct. Little intact forest remains on Anjouan and Mayotte, while much of the remaining forests that exist on Moheli and Grande Comore are badly degraded except at higher elevations where terrain is rugged or otherwise unproductive. It is thus likely that several plant species are at risk in these areas as well.

The natural forest habitats are highly fragmented due to human activities. Only some forest patches, mostly in the higher elevations, survive, and these are currently under heavy pressure. The largest remaining block of forest is on the slopes of Mount Karthala on Grande Comore. On Anjouan there are two remaining forest tracts of approximately 10 km2 in extent. This provides the only remaining habitat for the surviving population of the Anjouan scops owl (Otus capnodes) as well as the majority of habitat for the Livingstone’s fruit bat (Pteropus livingstonii). On Mayotte forests still remain on Mounts Sapéré, Bénara, and Choungi. A captive breeding program for Livingstone’s fruit bat is well established with over 2 dozen individuals being studied in captivity in Bristol Zoo and the Durrell Wildlife Conservation Trust.

None of the remaining forest areas are protected. Reserves have been proposed for several areas (including Mount Karthala), but this has not yet been established. There are just three protected areas in this ecoregion, the Saziley National Park on Mayotte, Lake Dziani Boudouni, a Ramsar wetlands site, and the Moheli Marine park including the Moheli islets, both on Moheli. Creation of a Coelacanth Marine Park is currently in process on the southern end of Grande Comore.

Types and Severity of Threats

All mature forest habitats on the Comoros Islands are highly threatened by agricultural expansion. Deforestation or conversion of land along rivers further changes the microclimatic conditions in the forest ecosystem and may severely affect temperature-sensitive species including bats and reptiles. The regenerating forests on the recent lava flows of Mount Karthala are not being farmed, as these lands are marginal for agriculture. Populations of other endemic species are in some cases critically small and extremely endangered, for example in several species of birds.

Current forest conservation measures are inadequate, and there is a high risk of large-scale extinction if appropriate protective measures are not implemented. Remaining forest patches are highly fragmented and represent predominantly montane habitats. Wildlife exploitation includes poaching of green sea turtles for local consumption. Collection of day geckoes for the pet trade is a potential threat to these species. Currently, hunting of fruit bats is not a problem, however as food resources become scarcer due to growing population, the local taboos against eating bats may disappear. Exotic species present a large problem - they are responsible for denuding smaller islands (Round Island) and have adverse effects on native vegetation on all islands. Introduced carnivores such as the Javan mongoose (Herpestes javanicus) have severe effects on ground-nesting bird populations, and some introduced exotic plants out-compete or severely impact native plant species.

Justification of Ecoregion Delineation

The Comoros Islands were included with the African mainland in White’s ‘coastal mosaic’ vegetation unit. However, it is considered a distinct ecoregion because the island group is separated from both Madagascar and the African mainland, and posses a high level of endemism in various taxa, particularly birds.

Additional Information on this Ecoregion

Further Reading

  • Adjanahoun, E. J., L. Aké Assi, A. Ahmed, J. Eymé, S. Guinko, A. Kayonga, A. Keita, and M. Lebras. 1982. Contributions aux études ethnobotaniques et floristiques aux Comores. ACCT, Paris.
  • Adler, G. H. 1994. Avifaunal diversity and Endemism on Tropical Indian Ocean Islands. Journal of Biogeography, 21:85-95.
  • Desegaulx de Nolet, A. 1984. Lépidoptères de l’Océan Indien: Comores, Mascareignes, Seychelles. ACCT, Paris.
  • Henkel, F. M., and W. Schmidt. 2000. Amphibians and Reptiles of Madagascar and the Mascarene, Seychelles, and Comoro Islands. Krieger Publishing Co., Florida. ISBN: 1575240149
  • Hilton-Taylor, C. 2000. The 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom. ISBN: 2831705657
  • Louette M. 1988. Les oiseaux des Comores. Mus. Roy. Afr. Centrale. Annales, Série IN-8 n 255. Tervuren.
  • Moulaert, N. 1998. Etude et conservation de la forêt de Mohéli (RFI Comores), massif menacé par la pression anthropique. Communauté française de Belgique: Faculté Universitaire des Sciences Agronomiques de Gembloux, Belgique.
  • Sinclair, I., and O. Langrand. 1998. Birds of the Indian Ocean Islands. Struik Publishers, Cape Town. ISBN: 1868720357
  • Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wege. 1998. Endemic Bird Area of the World: Priorities for biodiversity conservation. BirdLife Conservation Series No. 7, BirdLife International, Cambridge. ISBN: 0946888337
  • Stuart, S. N., R. J. Adams, and M. D. Jenkins. 1990. Biodiversity in Sub-Saharan Africa and its Islands: Conservation, Management, and Sustainable Use. Occasional Papers No. 6. IUCN Species Survival Commission. ISBN: 2831700213
  • Thibault, J. C., and I. Guyot, editors. 1988. Livre Rouge des Oiseaux Menaces des Regions Francaises D’outre-mer. International Council for Bird Preservation, France.
  • White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris. ISBN: 9231019554
  • World Conservation Monitoring Center. 1993. Ecologically Sensitive Sites in Africa. Volume III: South-Central Africa and Indian Ocean. The World Bank, Washington D.C.
  • WWF and IUCN. 1994. Centers of plant diversity. A guide and strategy for their conservation. Volume 1. Europe, Africa, South West Asia and the Middle East. IUCN Publications Unit, Cambridge, United Kingdom

Disclaimer: This article contains information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

 

Glossary

Citation

Fund, W. (2012). Comoros forests. Retrieved from http://www.eoearth.org/view/article/151399

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