Ascension scrub and grasslands

Last updated
Ascension scrub and grasslands
ASCENSION ISLAND SOUTHEAST BAY.jpg
Southeast Bay on Ascension Island
Ascension Island Location2.jpg
location of Ascension Island
Ecology
Realm Afrotropical
Biome tropical and subtropical grasslands, savannas, and shrublands
Geography
Area93 km2 (36 sq mi)
Country United Kingdom
Overseas territory Saint Helena, Ascension and Tristan da Cunha
Conservation
Conservation status Critical/endangered [1]
Protected0 km2 (0%) [2]

The Ascension scrub and grasslands ecoregion covers the dormant volcano, Ascension Island in the Atlantic Ocean. 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. However the seabird populations on Ascension Island itself have been severely affected by introduced species, especially cats, which were the subject of an eradication campaign between 2002 and 2006. [3]

Contents

Geography

Map of Ascension Island Labelled map of Ascension Island.svg
Map of Ascension Island

Ascension is 97 km.2 The island lies in the South Atlantic Ocean near the equator, 1700 km off the coast of Africa. The island is about a million years old and is volcanic in origin. [1] Volcanic activity occurred as recently as 1000 years ago. Most of the island is covered with young volcanic soils, including lava fields and cinder deposits.

The highest peak is Green Mountain at 859 metres elevation.

Ascension has 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 Saint 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.

Climate

Ascension Island has a subtropical semi-arid climate. Temperatures range from 10 to 32 °C. Mean annual rainfall is 709 mm. Rain showers occur year-round, with slightly higher rainfall during the summer months (January to April). [1] Trade winds are generally from the southeast. As moisture-bearing winds ascend Green Mountain, they cool and create orographic precipitation as both mist and rain. [4]

Flora

The natural vegetation of the island was dry grassland and scrubland, with few if any trees. Prior to human settlement the island had 25 to 30 species of plants, ten of which were endemic. Endemic species include two shrubs ( Euphorbia origanoides and Oldenlandia adscensionis (possibly extinct)), two grasses ( Sporobolus durus (possibly extinct) and Sporobolus caespitosus ), and six ferns ( Asplenium ascensionis , Marattia purpurascens , Xiphopteris ascensionense , Pteris adscensionis , and Anogramma ascensionis ). [4] [1]

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. 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 it 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 (Gygis alba), Ascension frigatebirds, masked booby, brown booby, red-footed booby, red-billed tropicbird and white-tailed tropicbirds (known as boatswain birds), and petrels. The sooty tern, 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 and the Ascension night heron are extinct.

Ascension frigatebird (Fregata aquilana) Of the many seabird colonising Ascension's shores, the endemic frigatebird 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 frigatebird.

Green sea turtle (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 feral. 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 1960s. 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, preying 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.

See also

Related Research Articles

<span class="mw-page-title-main">Europa Island</span> French atoll in the Mozambique Channel

Europa Island, in Malagasy Nosy Ampela is a 28-square-kilometre (11 sq mi) low-lying tropical atoll in the Mozambique Channel, about a third of the way from southern Madagascar to southern Mozambique. The island had never been inhabited until 1820, when the French family Rosier moved to it. The island officially became a possession of France in 1897.

<span class="mw-page-title-main">Frigatebird</span> Family of seabirds (Fregatidae)

Frigatebirds are a family of seabirds called Fregatidae which are found across all tropical and subtropical oceans. The five extant species are classified in a single genus, Fregata. All have predominantly black plumage, long, deeply forked tails and long hooked bills. Females have white underbellies and males have a distinctive red gular pouch, which they inflate during the breeding season to attract females. Their wings are long and pointed and can span up to 2.3 metres (7.5 ft), the largest wing area to body weight ratio of any bird.

<span class="mw-page-title-main">Ascension frigatebird</span> Species of bird

The Ascension frigatebird is a seabird of the frigatebird family Fregatidae which breeds on Boatswain Bird Island and Ascension Island in the tropical Atlantic Ocean.

Cosmoledo Atoll is an atoll of the Aldabra Group and belongs to the Outer Islands of the Seychelles, and is located 1,029 km (639 mi) southwest of the capital, Victoria, on Mahé Island.

<span class="mw-page-title-main">Island restoration</span>

The ecological restoration of islands, or island restoration, is the application of the principles of ecological restoration to islands and island groups. Islands, due to their isolation, are home to many of the world's endemic species, as well as important breeding grounds for seabirds and some marine mammals. Their ecosystems are also very vulnerable to human disturbance and particularly to introduced species, due to their small size. Island groups, such as New Zealand and Hawaii, have undergone substantial extinctions and losses of habitat. Since the 1950s several organisations and government agencies around the world have worked to restore islands to their original states; New Zealand has used them to hold natural populations of species that would otherwise be unable to survive in the wild. The principal components of island restoration are the removal of introduced species and the reintroduction of native species.

Aride Island is the northernmost granitic island in the Seychelles. A nature reserve, it is leased and managed by the Island Conservation Society of Seychelles.

<span class="mw-page-title-main">Great frigatebird</span> Species of bird (Fregata minor)

The great frigatebird is a large seabird in the frigatebird family. There are major nesting populations in the tropical Pacific Ocean, such as Hawaii and the Galápagos Islands; in the Indian Ocean, colonies can be found in the Seychelles and Mauritius, and there is a tiny population in the South Atlantic, mostly on and around St. Helena and Boatswain Bird Island.

<span class="mw-page-title-main">Campbell Islands</span> Island group in New Zealand

The Campbell Islands are a group of subantarctic islands, belonging to New Zealand. They lie about 600 km south of Stewart Island. The islands have a total area of 113 km2 (44 sq mi), consisting of one big island, Campbell Island, and several small islets, notably Dent Island, Isle de Jeanette Marie, Folly Island, Jacquemart Island, and Monowai Island. Ecologically, they are part of the Antipodes Subantarctic Islands tundra ecoregion. The islands are one of five subantarctic island groups collectively designated as a World Heritage Site by UNESCO.

<span class="mw-page-title-main">Lesser frigatebird</span> Species of bird

The lesser frigatebird is a seabird of the frigatebird family Fregatidae. At around 75 cm (30 in) in length, it is the smallest species of frigatebird. It occurs over tropical and subtropical waters across the Indian and Pacific Oceans as well as off the Atlantic coast of Brazil.

<span class="mw-page-title-main">Boatswain Bird Island</span> Island off the coast of Ascension Island

Boatswain Bird Island, also spelt Boatswainbird Island, is a small island some 270 metres (300 yd) off the east coast of Ascension Island in the South Atlantic Ocean with an area of approximately 5.3 ha. It is administered from Georgetown on Ascension, which is part of Saint Helena, Ascension and Tristan da Cunha, an overseas territory of the United Kingdom. Boatswain Bird Island should not be confused with the nearby, much smaller, Boatswain Bird Rock, only about 10 by 5 metres in size, located 570 metres (620 yd) south-east of the island and 360 metres (390 yd) north-east of the coast of Ascension. The southern coast of the island has an impressive natural arch.

<span class="mw-page-title-main">Fauna of the Cocos (Keeling) Islands</span>

The terrestrial fauna of the Cocos (Keeling) Islands is unsurprisingly depauperate, because of the small land area of the islands, their lack of diverse habitats, and their isolation from large land-masses. However, the fauna dependent on marine resources is much richer.

<span class="mw-page-title-main">Phillip Island (Norfolk Island)</span> Island near Norfolk Island

Phillip Island is an island located 6 km (3.7 mi) south of Norfolk Island in the Southwest Pacific, and is part of the Norfolk Island group. It was named in 1788 by Lieutenant Philip Gidley King after Arthur Phillip, the first Governor of New South Wales. Phillip Island is part of the Australian external territory of Norfolk Island, and is included in Norfolk Island National Park, as is neighbouring Nepean Island and about 10 percent of Norfolk Island proper.

Saint Helena, Ascension Island and Tristan da Cunha, as well the other uninhabited islands nearby, are a haven for wildlife in the middle of the Atlantic Ocean. The islands are or were home to much endemic flora and fauna, especially invertebrates, and many endemic fish species are found in the reef ecosystems off the islands. The islands have been identified by BirdLife International as Important Bird Areas for both their endemic landbirds and breeding seabirds.

<span class="mw-page-title-main">Wildlife of Cape Verde</span> Endemic species of the West African island nation

The wildlife of Cape Verde is found across its archipelago of ten islands and three islets, albeit in smaller numbers of species than mainland Africa. Each volcanic island within the archipelago is unique, and each of them have parks under their jurisdiction, by decree promulgated by the Cape Verde government. Located just off the west coast of Africa, the total land area of the island nation is 4,564 square kilometres (1,762 sq mi).
With the exception of bats, there are no truly endemic species of mammal on Cabo Verde; historically, the archipelago was only accessible to creatures with the ability to fly or swim, or to be brought by humans. The islands were first explored in 1456, but not actually settled until 1462; humans brought their livestock with them, including donkeys, pigs, cattle and goats—many of the latter are now so wild, they resemble mainland ibex, and are considered endemic “by default”.
In the centuries since settlement began, more mainland species would make their way with waves of settlers. There are no snakes present on the archipelago, which has allowed for the proliferation of many other species of other herpetiles, such as geckos, frogs and lizards. The main predators of these reptiles and amphibians would be the various birds of prey and raptors present, including the Egyptian vulture, Eurasian buzzard, kestrel, osprey, peregrine falcon, and the rare Cape Verde kite. This kite species is currently threatened by extinction but may yet be observed on Boa Vista and Maio.

<span class="mw-page-title-main">Southern Indian Ocean Islands tundra</span> Ecoregion of several subantarctic islands in the southern Indian Ocean

The Southern Indian Ocean Islands tundra is a tundra ecoregion that includes several subantarctic islands in the southern Indian Ocean.

<span class="mw-page-title-main">Ascension Island</span> British Overseas Territory in the South Atlantic Ocean

Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about 1,000 miles (1,600 km) from the coast of Africa and 1,400 miles (2,300 km) from the coast of South America. It is governed as part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha, of which the main island, Saint Helena, is around 800 miles (1,300 km) to the southeast. The territory also includes the sparsely populated Tristan da Cunha archipelago, 2,300 miles (3,700 km) to the south, about halfway to the Antarctic Circle.

The Desecheo National Wildlife Refuge is a National Wildlife Refuge in Puerto Rico. It is part of the Caribbean Islands National Wildlife Refuge Complex.

<span class="mw-page-title-main">Introduced mammals on seabird breeding islands</span>

Seabirds include some of the most threatened taxa anywhere in the world. For example, of extant albatross species, 82% are listed as threatened, endangered, or critically endangered by the International Union for Conservation of Nature. The two leading threats to seabirds are accidental bycatch by commercial fishing operations and introduced mammals on their breeding islands. Mammals are typically brought to remote islands by humans either accidentally as stowaways on ships, or deliberately for hunting, ranching, or biological control of previously introduced species. Introduced mammals have a multitude of negative effects on seabirds including direct and indirect effects. Direct effects include predation and disruption of breeding activities, and indirect effects include habitat transformation due to overgrazing and major shifts in nutrient cycling due to a halting of nutrient subsidies from seabird excrement. There are other invasive species on islands that wreak havoc on native bird populations, but mammals are by far the most commonly introduced species to islands and the most detrimental to breeding seabirds. Despite efforts to remove introduced mammals from these remote islands, invasive mammals are still present on roughly 80% of islands worldwide.

<span class="mw-page-title-main">Society Islands tropical moist forests</span>

The Society Islands tropical moist forests is a tropical and subtropical moist broadleaf forests ecoregion in the Society Islands of French Polynesia.

<span class="mw-page-title-main">Guadalupe Island Biosphere Reserve</span> Natural reserve in Mexico

The Guadalupe Island Biosphere Reserve,, is located in the Pacific Ocean and is part of Baja California state of Mexico. The Reserve consists of Guadalupe Island and several small islands nearby plus a large expanse of surrounding ocean. The Reserve was created by the government of Mexico on 25 April 2005 and is located 250 kilometres (160 mi) from the mainland. The Reserve is 4,770 square kilometres (1,840 sq mi) in size of which 263 square kilometres (102 sq mi) is land and the remainder is water.

References

  1. 1 2 3 4 "Ascension scrub and grasslands". Terrestrial Ecoregions. World Wildlife Fund.
  2. Dinerstein, Eric; Olson, David; et al. (June 2017). "An Ecoregion-Based Approach to Protecting Half the Terrestrial Realm". BioScience. 67 (6): 534–545. doi: 10.1093/biosci/bix014 . PMC   5451287 . PMID   28608869.{{cite journal}}: CS1 maint: date and year (link) Supplemental material 2 table S1b.
  3. Ratcliffe, N.; Bell, M.; Pelembe, T.; et al. "The eradication of feral cats from Ascension Island and its subsequent recolonization by seabirds". Oryx. 44 (1): 20–29. doi: 10.1017/S003060530999069X .
  4. 1 2 Catling DC, Stroud S (2012). "The Greening of Green Mountain, Ascension Island". In: Joachim M, Silver M (eds) Post-Sustainable: Blueprints for a Green Planet. Metropolis Books, New York. http://faculty.washington.edu/dcatling/Catling2012_GreenMountainSubmitted.pdf. Accessed 4 November 2020.