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South Atlantic Ocean

St. Helena, one of the most remote islands in the world, is of global importance for its unique biodiversity. Naturally colonized millions of years ago, the island became a refuge for its own unique species as well as for certain taxa that disappeared from the mainland. Human exploitation of the island’s natural resources for over 450 years lead to the degradation and erosion of large areas of land, which are now called the "Crown Wastes". This is considered to be one of the first documented environmental disasters instigated by humans. A small amount of progress has been made in recovering St. Helena’s lost habitat.

  • Scientific Code
    (AT0720)
  • Ecoregion Category
    Afrotropical
  • Size
    50 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Location and General Description
St. Helena Island (15.95º S, 5.72º W) is in the South Atlantic Ocean, 1,950 km west of the African Coast. About 14 million years old, St. Helena is the deeply eroded summit of a composite volcano. The resulting topography is quite dramatic. Plugs, domes, and dykes from the volcanoes create striking formations with names such as Lot, Lot's Wife, and the Gates of Chaos. The island covers 122 km2, with coastal cliffs of 300 m, cut by a few steep-sided valleys. Soils are heavy acidic clay, and mountain streams are present. The high point of the island, Diana’s Peak, reaches 823 m. The climate is dry subtropical, 15-32°C, with an annual mean rainfall of 152 mm. Rainfall is somewhat higher in the hills.

João da Nova discovered the island on May 21, 1502; now feast day for St. Helena in the Eastern Church. It was visited again in 1588 by Captain Thomas Cavendish aboard the HMS Desire and soon became a port of call for ships en route between the East Indies and Europe. St. Helena’s first inhabitants were employees of the trading companies and English settlers, who also brought slaves from South Asia, the East Indies, and Madagascar. By 1673 nearly half of the island’s inhabitants were slaves, until emancipation was achieved between 1826 and 1836. St. Helena became famous when Napoleon was exiled to the island in 1815; he died there in 1821. During the Zulu wars, the island was used again as a place of exile for Zulu warriors, and then for Boer prisoners during the Boer wars at the turn of the 20th century. St. Helena is a British colony, with its capital and port at Jamestown. The island of Ascension and the Tristan da Cunha Island group, both separate ecoregions, are dependencies of St. Helena.

It is believed that St. Helena once had substantial forests at elevations ranging between 400 and 600 m, primarily composed of gumwood (Commidendrum robustum) with smaller amounts of bastard gumwood (Commidendrum rotundifolium) (Cronk 1986). Introduced goats between the island’s discovery in 1502 and settlement in 1659 fragmented these forests, though large wooded areas still persisted. Remaining forest was then virtually eradicated during the 18th century through extensive cutting for firewood and the grazing of stock animals. A small gumwood stand survives at Peak Dale; the remainder of the island is covered by pasture, abandoned flax plantations, replanted woodland, dry rocky lowland, and some semi-natural shrubland vegetation (UNEP 1990). Colonists of the regenerating shrublands include prickly pear (Opuntia vulgaris), wild current (Lantana camara), wild mango (Schinus terebinthifolius), wild coffee (Chrysanthemoides monilifera), cedar (Juniperus bermudiana), aloe (Furcraea gigantica), pine (Pinus pinaster), spoor (Pittosporum viridiflorum), creeper (Carpobrotus edulis), yellow pops (Tecoma stans), and willow (Acacia longifolia) (Kendle and Rose Undated). In the early 1900’s, St. Helena’s economy became almost totally dependent on the production of New Zealand flax (Phormium sp.) , used to make rope and string. Flax had been planted over much of the island by the time the demand for the crop disappeared in 1966. Though there has been an intentional effort to clear the plant since then, flax still covers some interior areas of St. Helena.

Due to St. Helena’s isolation, the island was a refuge for many endemic species. It is believed that many of the island’s native plants are relicts of a primitive flora that was once widespread and that colonized the island as many as 10 million years ago (Cronk 1989). An example is seen in the tree fern (Dicksonia arborescens), which has been on St. Helena for at least 9 million years but no longer occurs in its likely source area of Africa. This type of relict endemic is frequent on islands, and is an important remnant of biodiversity that has disappeared elsewhere (Cronk 1997). The island’s native flora was composed of about 70 species of flowering plants and ferns, 60 of which are endemic in 10 endemic genera. These numbers place St. Helena in the top ranks of islands important for unique worldwide biodiversity. However, St. Helena has suffered severe degradation, and over half of the plants described in 1875 have since disappeared from the island. Currently, the remaining endemic plants are restricted to small remnants of their former habitat in protected spots such as steep cliffs or wastelands. Quite a few species once thought to be extinct have been rediscovered in recent times, including the local ebony (Trochetiopsis ebenus), St. Helena olive (Nesiota elliptica), false gumwood (Commidendrum spurium) and bastard gumwood (Commidendrum rotundifolium) (Spooner et al. 1993). While native vegetation declined many economically important plants were being introduced, and the total number of plant species present on St. Helena increased significantly. The flora now claims about 320 species, of which approximately 260 are naturalized aliens.

Biodiversity Features
St. Helena had several million years following colonization from the mainland to develop a rich and unique indigenous fauna. It only took a few hundred years of human interference to seriously diminish that diversity. Native birds have fared particularly poorly. The fossil record indicates that St. Helena most likely supported at least four endemic landbird species (two flightless rails, a cuckoo, and a hoopoe) when the first human settlers arrived (Stattersfield et al. 1998). At present, the only endemic bird remaining is the St. Helena plover or wirebird (Charadrius sanctaehelenae), which is restricted to northern flatter portions of the island’s interior (Stattersfield et al. 1998). Charadrius sanctaehelenae is closely related to Kittlitz's sand plover (C. pecarius) of Africa, though it is larger and has different markings. It is currently thought to be steadily declining. Birdlife International classifies St. Helena as a Secondary Area of conservation importance. The invertebrate fauna of St. Helena has undergone some repetitive speciation and adaptive radiation, resulting in many endemic species (Ashmole and Ashmole 1997). There are 157 endemic beetles recorded, including a ground beetle (Aplothorax burchelli), which is endangered; the endemic St. Helena earwig (Labidura herculeana), which was rediscovered in 1965-67, has not been found live since and is also considered to be endangered (UNEP 1990). No mammals or reptiles occurred on St. Helena before introduction by humans.

Current Status
Fragmentation and loss of St. Helena’s natural vegetation began before the island was settled. Goats were released in 1533 to provide meat for passing ships. A lack of any management allowed these herds to grow dramatically, and flocks "near a mile long" were noted in 1588. Sheep and pigs were released as well, trees were cut for timber, and fruits and vegetables were planted. St. Helena’s unusual and remarkable flora and fauna followed the course of ecological destruction common to many oceanic islands. The majority of the original vegetation has been destroyed, and over half of the island is covered by wastelands of bare soil and sparse, mostly exotic scrub (Kendle and Rose Undated). Less then one percent of the island retains native semi-natural forest in isolated remnants (Kendle and Rose Undated). Some progress has been made in restoration of habitat in the last decades, and the island government has established an "Endemic Section" and a few conservation areas, emphasizing environmental awareness (Smith 1997). Diana's Peak is a National Park, and wardens work to preserve endemic species such as tree ferns and dogwoods that have been inundated by introduced plants such as the New Zealand flax.

Types and Severity of Threats
St. Helena continues to be threatened by exotic species and exploitation by humans. A severe drought occurred in 1984 (UNEP 1990). Water is a scarce resource on St. Helena for humans and nature alike, and drought poses a significant threat to the fragile and isolated ecosystem. The island is far from being economically self-sufficient and depends largely on funding from the UK. There has been a push to promote tourism as a source of revenue, though the island has never been accessible by airplane due to its mountainous terrain. Currently, A British company, the St. Helena Leisure Corporation (SHELCO) has made proposals "to develop communications and tourist amenities on the island by constructing a privately-funded airport, a world-class international quality resort hotel, and a superior 18-hole championship-standard golf course." It appears that the project has strong support from the local community. The proposed airstrip would be levelled near a spot called Prosperous Bay Plain, a 150ha area of semi-desert supporting the native shrub, Suaedia fruticosa, and an endemic annual, Hydrodea cryptantha as well as many endemic invertebrates, some of which are known exclusively from this plain (Cairns-Wicks 1999). While Prosperous Bay Plain is also thought to be closer to the endemic wirebird’s original habitat than any other now existing on the island, the bird occurs here in much lower numbers than it does in non-native pasturelands. While not yet accepted, the construction of an airstrip would have many impacts beyond the rock-blasting and cut-and-fill alteration of the Prosperous Bay Plain area.

Justification of Ecoregion Delineation
St. Helena, in the South Atlantic Ocean, is one of the most remote islands in the world. Naturally colonized as long as 10 million years ago, the island became a refuge for endemic species as well as for certain taxa that disappeared from the mainland. It is believed that many of the island’s native plants are relicts of a primitive flora that was once widespread in Africa. It is designated as a Birdlife International Secondary Area due to the presence of one endemic plover; the island also supports endemic invertebrates and plants.

References
Ashmole, N. P. and Ashmole, M. J. 1997. The land fauna of Ascension Island: New data from caves and lava flows, and a reconstruction of the prehistoric ecosystem. Journal of Biogeography 24:549-589.

Cairns-Wicks, R. 1999. Environmental Screening Note: Air Access to St Helena (Abridged). Retrieved (2001) from: <http://www.shelco.sh/studies/environmental.asp>.

Cronk, Q. C. B. 1986. The decline of the St. Helena gumwood Commidendrum robustum. Biological Conservation 35:173-186.

Cronk, Q. C. B. 1989. The past and present vegetation of St Helena. Journal of Biogeography 16:47-64.

Cronk, Q. C. B. 1997. Islands: Stability, diversity, conservation. Biodiversity and Conservation 6:477-493.

Kendle, A. D. and J. E. Rose. Undated. The Role of Native and Alien Species in the Recovery from Desertification of St. Helena Island. Retrieved (2001) from: <http://www.desertification.it/doc/AlgheroWEB/Rose%20J.%20E.htm>.

Smith, D. 1997. The progress and problems of the 'Endemic Section' of St. Helena Island. Oryx 31:218-224.

Spooner, B., T. Upson, A. D. Kendle, and G. Drucker. 1993. Environmental Profile of St. Helena.M. Mander, B. Dala-Clayton, and A. Bass, editors. Sustainable Environment and Development Strategy and Action Plan for St Helena. Vol 2. RBG Kew and the International Institute for Environment and Development, Government of St Helena, St Helena Island.

Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. 1. Wege. 1998. Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. BirdLife Conservation Series No.7., Cambridge, U.K.

UKOTCF. 1999. Annual Report 1998/99 - UK Overseas Territories Conservation Forum. Retrieved (2001) from: <http://www.ukotcf.org/report99.htm>.

UNEP. 1990. Island Directory - Islands of St. Helena (United Kingdom), (UNEP) United Nations Environment Programme, Geneva, Switzerland. Retrieved (2001) from: <http://www.unep.ch/islands/INN.htm#917>.

Prepared by: Leann Trowbridge
Reviewed by: In process

 

 

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