Ascension scrub and grasslands
Encyclopedia
The Ascension scrub and grasslands ecoregion
Ecoregion
An ecoregion , sometimes called a bioregion, is an ecologically and geographically defined area that is smaller than an ecozone and larger than an ecosystem. Ecoregions cover relatively large areas of land or water, and contain characteristic, geographically distinct assemblages of natural...
covers the dormant volcano, Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
in the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
. As well as shrubs and grasses wildlife on the island includes a range of unique flora and fauna. In particular the surrounding islets are important havens for many seabirds, although the seabird populations on Ascension island itself have been severely affected by introduced species, particularly cats.
Location and description
Ascension Island lies in the Atlantic near the equator, 1700 km off the coast of AfricaAfrica
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. The island still bears relics of its volcanic history including lava fields and cinder. Ascension is 97km2, with a population of approximately 900. The residents are mainly employees and their families, often on short term contracts with the Ascension Island Government, the military (Royal Air Force and United States Air Force) and commercial operations. The majority of food and other goods are imported from the UK and South Africa. The Royal Mail Ship brings in supplies from St Helena on a regular basis. The USAF air service provides links with Florida and Antigua. The UK Ministry of Defence air service provides links with the Falkland Islands and the UK.
Flora
There were never many trees on the island, which is covered by either desert or grass and shrub including some endemic: Euphorbia origanoidesEuphorbia origanoides
Euphorbia origanoides is a species of plant in the Euphorbiaceae family. It is endemic to Ascension Island a dependency of the UK overseas territory of Saint Helena. Its natural habitats are introduced vegetation. It is threatened by habitat loss.-Source:* Gray, A. 2003. . Downloaded on 21...
, Marattia purpurascens
Marattia purpurascens
Ptisana purpurascens is a large fern belonging to the botanical family Marattiaceae. It has a globular rhizome with stipule-like fleshy outgrowths. The leaves are dark green, twice pinnate and up to 1 metre long. Every pinnule has up to six pairs of leaflets. The petioles are dark-purplish, hence...
, Asplenium ascensionis
Asplenium ascensionis
Asplenium ascensionis is a species of fern in the Aspleniaceae family. It is endemic to Ascension Island. Its natural habitats are introduced vegetation. It is threatened by habitat loss.-Source:* Gray, A. 2003. . Downloaded on 20 August 2007....
, Xiphopteris ascensionense
Xiphopteris ascensionense
Xiphopteris ascensionense is a species of fern in the Grammitidaceae family. It is endemic to Ascension Island. Its natural habitats are introduced vegetation. It is threatened by habitat loss.-Source:...
, Pteris adscensionis
Pteris adscensionis
Pteris adscensionis is a fern species in the Pteridaceae family. It is endemic to Ascension Island, and there are thought to be fewer than 500 individuals left in the wild. Its natural habitat has been severely reduced to the large number of species introduced to the island when it was first...
, Sporobolus caespitosus
Sporobolus caespitosus
Sporobolus caespitosus is a species of grass in the Poaceae family.It is endemic to Ascension Island, in the South Atlantic Ocean, where it is known only from the weather side of the Green Mountain area, where it occupies an area of less than 0.5 km²...
and Anogramma ascensionis
Anogramma ascensionis
Anogramma ascensionis is a species of fern in the Pteridaceae family that is endemic to Ascension Island, a volcanic island in the South Atlantic Ocean. It is one of eight putative species in the Anogramma genus. It was thought to have become extinct due to habitat loss, until four plants were...
.
Most of the vegetation on Ascension Island today has been introduced by humans. Some of these species have spread dramatically and now occur throughout the Island. Approximately 25 species of plant are native and ten of these are considered to be endemic (unique) to Ascension. None of the remaining endemic species are common and their ranges have been reduced due to their inability to compete with the introduced species. The Ascension Island Conservation Department are working in collaboration with the Royal Botanic Garden, Kew on an OTEP (Overseas Territories Environmental Programme) funded Endemic Plants project. Experts from the UK Overseas Territories Team at Kew advise on propagation techniques, ex-situ cultivation and the re-introduction of endangered species. Horticultural protocols for each species are to be outlined, these will be used to improve local collections and further develop ex-situ plant collections. The protocols require a lot of trial and error work to identify the most successful propagation methods for the endemic plants. Stedson Stroud has already successfully cultivated in large numbers three of the endemic species, Pteris adscensionis, Euphorbia origanoides and Sporobolus caespitosus. The clearing of invasive species on Green Mountain has created a restoration site for the reintroduction of endemic species on the mountain. The project work focuses on increasing the number of endemic species growing in cultivation and introducing these into the restoration areas.
Spurge (Euphorbia origanoides)
This is the only endemic lowland plant in Ascension. It suffers from encroaching invasive vegetation as well as feeding by introduced animals. Rats seek for moisture in its stems and roots, and insect pests also cause concern. The species is now limited to the most remote desert areas of the Island.
Fauna
Ascension Island is one of the most important warm-water seabird breeding sites in the tropical Atlantic. It supports over 400,000 seabirds of 11 species. The present size of the seabird populations are only a fraction of those found before the colonisation by man in 1815 and the subsequent introduction of feral cats to the Island. The Ascension Island Conservation Department, in partnership with the RSPB began a Seabird Restoration Project in 2001. The project was implemented by the Ascension Island Government, and assisted by the RSPB with funding from the Foreign and Commonwealth Office. Feral cats were eradicated from the Island, allowing the seabirds to return to nest on the mainland. The last known feral cat was found in February 2004, since then a feral cat monitoring programme has been taking place. Since the eradication of the feral cats the nesting success rate has improved and there are more birds in an increasing number of locations.Today the main breeding site is on nearby rat-free Boatswain Bird Island. Over 10,000 birds breed on this tiny island, which is home to Fairy Tern
Fairy Tern
The Fairy Tern is a small tern which occurs in the southwestern Pacific.There are three subspecies:* Australian Fairy Tern, Sterna nereis nereis - breeds in Australia...
(Gygis alba), Ascension Frigatebird
Ascension Frigatebird
The Ascension Frigatebird breeds only on the tiny Boatswain Bird Island just off Ascension Island in the tropical Atlantic Ocean. It formerly bred on the larger island, but was exterminated by introduced cats, Brown Rats, and human persecution.It breeds on the rocky slopes of Boatswainbird...
s, Masked Booby
Masked Booby
The Masked Booby, Sula dactylatra, is a large seabird of the booby family, Sulidae. This species breeds on islands in tropical oceans, except in the eastern Atlantic; in the eastern Pacific it is replaced by the Nazca Booby, Sula granti, which was formerly regarded as a subspecies of Masked Booby...
, Brown Booby
Brown Booby
The Brown Booby is a large seabird of the booby family, Sulidae. The adult brown booby reaches about in length. Its head and upper body are covered in dark brown, with the remainder being a contrasting white. The juvenile form is gray-brown with darkening on the head, wings and tail...
, Red-footed Booby
Red-footed Booby
The Red-footed Booby, Sula sula, is a large seabird of the booby family, Sulidae. As suggested by the name, adults always have red feet, but the colour of the plumage varies. They are powerful and agile fliers, but they are clumsy in takeoffs and landings...
, Red-billed Tropicbird
Red-billed Tropicbird
The Red-billed Tropicbird, Phaethon aethereus, also known as the Boatswain Bird is a tropicbird, one of three closely related seabirds of tropical oceans.-Distribution and habitat:...
and White-tailed Tropicbird
White-tailed Tropicbird
The White-tailed Tropicbird Phaethon lepturus, is a tropicbird, smallest of three closely related seabirds of the tropical oceans and smallest member of the order Phaethontiformes. It occurs in the tropical Atlantic, western Pacific and Indian Oceans...
s (known as Boatswain Birds), and petrels. The Sooty Tern
Sooty Tern
The Sooty Tern, Onychoprion fuscatus , is a seabird of the tern family . It is a bird of the tropical oceans, breeding on islands throughout the equatorial zone. Colloquially, it is known as the Wideawake Tern or just wideawake...
, known locally as the Wideawake Tern because of its distinctive call, is the most common breeding seabird on the main island, and the airport is named after it. The Ascension Rail is extinct.
Ascension frigate bird (Fregata aquilana)
Of the many seabird colonising Ascension’s shores, the endemic frigate bird is the most impressive. Due to predation by cats these birds are now found on Boatswainbird Island, but as feral cats have been eradicated from Ascension, it is hoped they will soon follow the other seabirds back to the main Island.
Giant pseudoscorpion (Garypus giganteus)
Ascension is home to a remarkable pseudoscorpion fauna. The most impressive of these tailless scorpion-like creatures is the giant pseudoscorpion, largest of its kind. Predation by rodents and invertebrates on the mainland has limited its distribution to the very isolated Boatswainbird Island, where it lives alongside the endemic frigate bird.
Green turtles (Chelonia mydas)
Ascension holds the second largest breeding site for the green turtle in the Atlantic. This species is dependent on sandy beaches to lay their eggs, and the beaches require regular clearing of invasive plants. Apart from the native landcrabs and endemic frigates, the hatchlings are now taken by mynas.
Threats
Since its discovery in 1501 a number of plants and animals have been introduced by settlers on the island, there are no native mammals to the islands and several of the introduced species have gone feralFeral
A feral organism is one that has changed from being domesticated to being wild or untamed. In the case of plants it is a movement from cultivated to uncultivated or controlled to volunteer. The introduction of feral animals or plants to their non-native regions, like any introduced species, may...
. Cats in particular have been a threat to the seabird populations and steps are now being taken to reduce the populations of both cats and rats in order to encourage the return of breeding seabirds. Meanwhile the Mexican thorn bush (Prosopis juliflora), another introduced species, has become a serious impediment to the breeding turtles, who lay their eggs on the beaches, and housing development on the island threatens many habitats.
Invasive species
Mexican Thorn (Prosopis juliflora)
This shrub was introduced to stabilise land near new buildings in Two Boats village during the 1960’s. It now forms a thick shrubland in drier parts of the Island. It has completely replaced the native vegetation in these areas and threatens bird grounds as well as turtle laying beaches.
Guava (Psidium guajava)
Guava is best known as a refreshing fruit, however, unfortunately on Ascension the fruit it not harvested due to its acidity. Guava causes significant problems in fragile environments such as Ascension Island. This species is one of the first shrubs to cover over sparsely vegetated areas. It can tolerate both hot desert areas as well as cool moist mountain air, and forms thickets that compete with native plants for water and light.
Koster’s Curse (Clidemia hirta)
This is one of the species that now occurs where a carpet of native and endemic ferns used to grow on Green Mountain. Along with many other introduced species it is capable of growing even in the last rocks which have so far acted as fern sanctuaries.
Common myna (Acridotheres tristis)
Myna birds were introduced as a way of tackling parasites on cattle, now absent from Ascension. They are opportunistic feeders and now feed on sooty tern eggs, turtle eggs and fruits of invasive species, acting as a dispersal agent. They are also noisy and clever pests in gardens, eating fruit and vegetables.
Black rat (Rattus rattus)
The black rat arrived to Ascension early in the Island’s history and they are still the only species of rat here. They abound in all parts of the Island, feeding on endemic as well as introduced plants, predating on small animals and competing with land crabs.
Threatened habitat - Mountain vegetation
The Green Mountain summit was once covered in a carpet of ferns with many endemic plants. Hardly any of this carpet now exists due to intensive efforts to increase vegetation in the mountain. Few small rocks still hold a number of endemic species, but even these areas are quickly being overwhelmed by invasive plants. Grazing animals also contribute to loss of native plants.