Prosperous Bay Plain
Prosperous Bay Plain is an area on the north-eastern coast of St Helena, and the site of St Helena Airport, opened in 2016. It falls within the district of Longwood.
Though St Helena is the main island of the British overseas territory of St Helena, Ascension and Tristan da Cunha, it was until 2016 without any airfield to join it to the modern world, relying instead on transport by sea. Prosperous Bay Plain was chosen for the airport as the only part of the island with sufficient level, land which even so required major work to provided a flat runway.
The plain is notable for its high invertebrate biodiversity.
Contents
Geography
Prosperous Bay Plain forms part of the eastern arid area of St Helena, and covers about 556 acres, comprising one of the largest areas of relatively level ground on the island. It was formed 8.5 million years ago by lava flows from St Helena’s Southwest Volcano. The surface of the plain is covered by rocks, grit and dust, with what little soil there is containing high concentrations of mineral salts.[1]
Until the construction of the airport, the plain contained a miniature, contained ecosystem: a 148-acre depression known as the Central Basin. With its shelter and its a level dusty base, this formed a miniature mature desert ecosystem.[1]
Vegetation
The climate of the plain is arid and plants are few, scattered and low-growing. Dusty areas and gullies are dominated by the native samphire Suaeda fruticosa. In rocky areas the more dominant plant is the introduced Hottentot fig (Carpobrotus edulis). On dry slopes, including those of the Central Basin, there are various chenopods, including the introduced saltbush Atriplex semibaccata. The plain holds a number of important populations of the island's endemic flora. The slopes of Dry Gut host the largest remaining group of barn fern (Ceterach haughtonii). Dry Gut is also home to the most abundant remaining population of the endemic boneseed, (Osteospermum sancta-helenae). Annual flushes of endemic babies'-toes (Hydrodea cryptantha), goosefoot (Chenopodium helenense) and neglected sedge (Bulbostylis neglecta) occur across the plain. There are a few scattered scrubwoods (Commidendrum rugosum), teaplants (Frankenia portulacifolia) and salad plant (Hypertelis acida), threatened endemics which may have grown more plentifully in the area in the past, before the introduction of exotic herbivores.[1][2]
Fauna
Birds
Before the discovery of St Helena in 1502, the plain was home to seabird breeding colonies. These disappeared after settlement of the island from predation by humans and feral cats. The only endemic land-bird still present is the critically endangered St Helena plover (the wirebird), of which the plain makes up 10% of its remaining habitat.[1]
Invertebrates
Prosperous Bay Plain is a biodiversity hotspot, home to an extraordinary concentration of endemic invertebrates, the area being the main evolutionary centre on the island for animals adapted to arid habitats. Some 35–40 species and six genera recorded in this limited area occur nowhere else in the world. The St Helena giant earwig used to inhabit the plain, and may still, although there have been no live records of it since 1967. The St Helena giant beetle may also be extinct.[1] The mollusc Nesopupa turtoni in the whorl snail family Vertiginidae, previously known only as a fossil and long presumed to be extinct, was discovered alive in a 2003 survey[3]
Conservation
Invertebrate habitats on the plain have been affected by many factors, including the systematic removal of loose and portable rocks for construction purposes, the formation of vehicle tracks, and the building of structures such as forts.
Nevertheless, the needs of man exceed those of the earwig, and the new St Helena Airport has proceeded, along with its access roads, terminal building, support structures and the panoly of modernity, requiring the destruction of part of the plain, including part of the Central Basin.[4]
Outside links
- Location map: 15°57’40"S, 5°39’18"W
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Ashmole, Philip; & Ashmole, Myrtle: The invertebrates of Prosperous Bay Plain, St Helena (2004), for the St Helena Government
- ↑ Lambdon, Phil. (2012). Flowering plants and ferns of St Helena. Pisces Publications, Newbury
- ↑ Ashmole, Philip; & Ashmole, Myrtle. (2004). Guide to Invertebrates of Prosperous Bay Plain, St Helena. Illustrated account of species found on the Eastern Arid Area (EAA), including Prosperous Bay Plain, Holdfast Tom and Horse Point Plain. Kidston Mill, Peebles
- ↑ St Helena Island news
- The battle for St Helena by Robin Stummer and Daniel Howden, 20 October 2005
