The invertebrates of Prosperous Bay Plain, St Helena a survey by Philip and Myrtle Ashmole September – December 2003 Commissioned by the St Helena Government and financed by the Foreign and Commonwealth Office

7.1.1. Background

Prosperous Bay Plain, in contrast, has been seen neither as an area to be proud of, nor as an area under threat. It has few endemic plants and the invertebrates are easily overlooked. The recent realisation that the plain is a biodiversity hotspot, deserving recognition at an international level, has come in parallel with the origin of an unprecedented threat, in the form of potential airport development. This is therefore an appropriate time to encourage within the local community a sense of ownership and pride – before the bulldozers arrive.

In considering issues of air access to St Helena, it is worth remembering that if the island is to develop special-interest tourism, the natural environment is one of the major assets. It need not matter that the endemic animals of Prosperous Bay Plain are mainly small and hard to see; international recognition of their importance and publicity relating to them in tourist brochures can help to make the island attractive to visitors.

One way to develop pride in the area is for the St Helena Government and private individuals to cooperate in cleaning up the area in advance of airport development, and to embark on a modest programme of ecological restoration.

The concrete foundations of old aerials are still present on the plain, refuse has been dumped in several places, and unauthorised stone removal has left scars and destroyed animal habitats in many places. Relatively recently, engineers cut a shallow exploratory trench across the Central Basin and made various minor excavations, but no attempt was made to repair this environmental damage.

In addition, vehicle tracks criss-cross Prosperous Bay Plain (Plate 6g). On the open expanses of plain (including the Central Basin) there is a temptation for drivers of 4 x 4 vehicles and motorbikes to wander anywhere. This produces scars (especially visible in the basin and on steep slopes) and damages animal populations. During our work, we became increasingly aware how important it was to drive only on established tracks. We hope that publicity and consultation with ‘motocross’ enthusiasts can ensure that in future, sport driving activities are concentrated in areas where they will do least damage. Removal of existing scars, especially in the Central Basin, would considerably enhance the scenic value of the area.

Degradation of natural environments as a result of invasion by introduced plant species is a worldwide problem that is often especially severe on islands. It involves loss of native (often endemic) plants and animals and substitution of vegetation that is inappropriate though often luxuriant. In severe cases, this can undermine the pride of local human communities in their natural heritage and confuse discussions on conservation. However, where some native species still survive, as on Prosperous Bay Plain, there are opportunities for exciting initiatives in conservation and ecological restoration.

Protection of native plants and control of invasive introduced plants on PBP present significant challenges. Some native plants have already been lost or severely depleted, and a number of invasive introduced plants are present. The mat-forming Creeper Carpobrotus edulis has already replaced natural vegetation on much of the higher ground in the west of PBP and is tending to invade the Central Basin. This species, however, has the beneficial effect of limiting erosion of the high plateau areas such as Horse Point Plain. Furthermore, although this plant is not native to St Helena, it now clearly plays a significant ecological role, providing refuges for invertebrates (including many endemic species) and in some sense replacing the carpet of dead and decaying leaves that would have formed a carpet in the original Gumwood forests.

This conclusion has implications for immediate management, suggesting that although the spread of Creeper into Samphire dominated areas should be resisted, large scale removal of Creeper from areas where native vegetation is already absent would be misguided. We can, however, envisage the gradual re-establishment of Gumwoods and Scrubwoods leading eventually to accumulation of litter and re-establishment of the original microhabitats. At that stage, removal of Creeper would be appropriate. In the meantime, it is important to prevent the spread of Creeper into areas where it will compete with native plants or cover open ground that is a key resource for endemic animals, especially in the Central Basin (Plate 6h).

The spread of alien shrubs such as Prickly Pear cactus, Lantana and Wild Tobacco Nicotiana glauca on PBP is a wholly negative factor. Left unchecked, these species will probably make considerable changes to the area, leading to severe degradation of its community of native invertebrates. The low-growing Saltbush Atriplex semibaccata is already so well established in precipitous places that we see no way in which it could be eliminated or effectively controlled, and complete removal of Wild Tobacco is probably also impracticable, but a programme to limit spread of the other species is feasible and need not be costly, though it requires a formal initiative.

We believe that there will be major advantages in designating the Central Basin of Prosperous Bay Plain (Plate 2b) as a protected area. A legal framework for such designation is already in place and Regulations can be used to designate specific areas. A formally designated site on Prosperous Bay Plain, like the Peaks, will gain international recognition if it is adequately protected and publicised. Even if there is little for the tourist to see, its existence will be an added attraction, if St Helena aims at the eco-tourism market. Designation will also make it easier to attract funding for necessary environmental work.

Another important consideration is that the Central Basin of Prosperous Bay Plain is a readily identified and discrete element within a complex and barren landscape. The designation of such a clear natural entity as a special protected area will make immediate sense to the ordinary person, in a way that a line drawn along non-visible boundaries on a map could never do. This immediate recognition and mental labelling of the site will bring substantial benefits in relation to its protection and enhancement over the long term. If designation is linked with eventual prohibition of vehicle use within the basin (see Section 7.2.2.d) it will increase the sense that people have no right to inflict casual damage on an ecologically valuable habitat.