Natural History of the Island of St HelenaExtinction and Survival in the South Atlantic

by Myrtle and Philip Ashmole

This sketch of the human history of St Helena ignores the transformation of the island - over the same period - from a pristine, uninhabited, tropical paradise to an ecologically battered but still fascinating ecosystem dominated by the influence of humans. Myrtle and Philip Ashmole, biologists whose studies on St Helena and Ascension Island span four decades, have written a book on the natural history of the two islands which will be published this year by Anthony Nelson.

St Helena is an ancient island. Formed near the Mid-Atlantic Ridge more than 14 million years ago, it was so remote from any other land that only a few kinds of vagrant plants and animals managed to reach it without the help of humans. The plant colonists were species whose seeds could withstand prolonged immersion in seawater or could be transported by migrant birds, in their guts or stuck on their plumage or feet. Probably fewer than 100 species of higher plants colonised the island naturally, and some of these became extinct millions of years ago, perhaps as a result of intensive volcanic eruptions that covered much of the island with scorching lava. The survivors underwent profound evolutionary changes, while in many cases their closest relatives in Africa became extinct, so that the island is now home to a series of remarkable plants found nowhere else in the world.

The first animal colonists were doubtless seabirds, but these were gradually joined by a number of long-distance aerial migrant species - birds, insects and arachnids - helped to the island by meteorological disturbances originating in Africa. A few animals swam to the island, or drifted on logs, or hitch-hiked on other species. The small number of founding stocks provided a stimulus for evolution, which then ran riot, generating impressively high biodiversity. Some 400 animal species are endemic to St Helena (found only on the island) including no fewer than 77 species of weevils that probably evolved from only four or five groups of colonists.

When humans discovered St Helena, this extraordinary natural laboratory of evolution came under immediate threat. The native vegetation was devastated by goats and pigs, and later by the settlers and their slaves gathering firewood, felling timber for buildings and stripping bark for tanning. Alien animals such as large centipedes, mice, rats and cats preyed on the native fauna. The seals, turtles and seabirds were lost or decimated, and all but one of the endemic landbirds became extinct before they were even described by naturalists. Deforestation initiated severe erosion, and the whole outer part of the island became a spectacular but barren desert. A horde of introduced, invasive plants spread over the middle levels, and native trees survived only in tiny groups, mainly on the highest peaks and cliffs.

St Helena is still beautiful, and a fascinating place to visit. We spent six months on the island in 1994/95 and every day brought us new delights from the naturalist's point of view. However, since it is only a pale shadow of what it once was, we provide here a flashback to the day it was discovered. Though imaginary, it is based on the records of observant early travellers, knowledge derived from fossil evidence, and scientific studies of the remaining plants and animals.

Joao da Nova and the excited crew of his tiny Portuguese vessel came in sight of St Helena on 21st May, 1502, anchoring in a sheltered bay on the northwest of the island. A boat full of sailors was soon pulling in to the beach in the valley later known as Chapel Valley. The volcanic landscape was strange and rugged and the plants unfamiliar - hardly any of them known to the sailors from their explorations along the west coast of Africa.

It was animals, however, that first caught the men's attention. On the beach they found ridiculously tame seals, several of which they quickly clubbed to death to provide welcome fresh meat. The rocky slopes close to the valley mouth were occupied by swarms of seabirds and covered by guano that was dazzlingly white in the sun. Tropicbirds - solidly built birds providing a good deal of meat - were nesting in crevices, while boobies and noddies roosted and bred on the slopes. The birds were tame and easy to catch by hand, or to kill with sticks or stones. In the evening turtles came up the beach, and these the seamen turned on their backs and took on board alive the next day, to provide food for the homeward journey.

Chapel Valley had a stream, where water barrels were soon being filled. Nearby were thickets of Dwarf Ebony, with rich green leaves and beautiful white tulip-like flowers. The rockier slopes had scattered patches of the slightly succulent Salad Plant, which was tart and refreshing to eat raw. On the more level patches close to the sea were bizarre clumps of Baby's Toes, with swollen yellow-green stems and surprising, delicate, white flowers almost concealed in the tips of the stems.

The exploring party struggled on inland, at first forcing their way through thickets in the valley, but soon deciding to make for the rocky ridges on which the shrubs were more scattered. These shrubs included the Scrubwood, which they had seen from the sea, with straggly branches profiled against the edges of sheer cliffs; now on closer view it had showy white daisy flowers. As they pushed through the bushes they scattered clouds of tiny (and harmless) jumping bugs that had been feeding on the leaves. They also found slopes covered by the Tea Plant, a wiry, spreading bush with minute leaves and equally small white flowers, and branches swaying in the wind. In clefts in the rock were clumps of Old Father Live Forever, a geranium with swollen, shiny-barked stems hugging the rocks, hairy leaves and flowers nodding on long, slender stalks. These flowers were also white, setting a pattern that was to become more striking as they went further inland.

As they gained height and reached relatively level places, the sailors came to groves of real trees, but of quite an unfamiliar kind. Like the "cabbage-tree" that they encountered later, these Gumwoods and Bastard Gumwoods were "composite": relatives of dandelions and thistles, but here in abnormally large versions, forming trees with arching branches and clusters of flowers on long stalks. These were sticky plants, like their relatives the low-growing Scrubwoods, and the sailors' clothes and hands became covered with gum. When they needed a fire, the resinous Gumwood branches proved ideal, but the men were startled - when moving rocks to build the fireplace - by giant earwigs as much as three inches long and a black beetle also larger than any they had ever seen.

Climbing up through the woods, they blessed the fact that none of the plants were prickly, but were annoyed by the tough webs of an enormous, striped, black and white spider strung between the trees. They found no mammals or reptiles, but did see birds. In the open areas, and also in the drier woodlands, they came across a large, boldly patterned hoopoe which seemed reluctant to fly. In the woods there was a green cuckoo in the treetops, and they glimpsed small flightless rails - streaked brown birds with strong legs - as they scuttled away through the undergrowth; once they disturbed a larger rail - the size of a small chicken - but were unable to catch it although it too seemed unable to fly. When they reached a more level area they found plovers - later named Wirebirds - running on the ground under the Gumwoods and sometimes taking off in mild alarm.

In the moister uplands the Gumwood trees became mixed with the Redwood, a real timber tree that the sailors recognized as a relative of the Dwarf Ebony which they had seen lower down, but with pale green leaves and larger, drooping flowers that were white when fresh, changing to purplish when dying.

Only after a serious climb did the sailors reach the most striking vegetation on the island: the cabbage-tree woodland of the central highlands. The She-Cabbage and He-Cabbage Trees were both tall and slender, with large, fleshy leaves; conspicuous on these were hoary beetles with blunt snouts and slender, elbowed antennae held out in front as the insects moved slowly around. Other tree species forming the canopy were the False Gumwood, similar to the Gumwood that they had already seen, and the Whitewood, a small upright tree with a bushy crown.

Also present here, but more dominant on the mist-shrouded summit ridge that was reached by only a few energetic seamen, were Tree-ferns, recognizable as ferns but growing as high as a house, with enormous fronds spreading in the canopy. Their shaggy trunks - thicker than a man's leg and exuding red gum - acted as seedbeds for many of the other plants of this damp forest. The trees that thrived here were the Black Cabbage Tree, with spreading crown and glossy leaves, and the St Helena Olive and Dogwood; these last two species were quite different from the cabbage-trees and indeed unlike any trees that the sailors had ever seen.

Crawling on the Tree-ferns were many small yellow woodlice, thickly covered with sharp spikes, and when the sailors trod on rotting fern trunks they saw one of the large predatory ground beetles that lived in the galleries eaten away by their prey, the larvae of other beetles. At this level on the island, almost every animal that the sailors saw would have belonged to species found nowhere else in the world.

In gulleys on the mountainside, where trickles of water cut channels through the deep humus, were patches of Jellico, a spectacular giant relative of celery that towered over the sailors' heads; being starved for vegetables some of them took a cautious nibble, and finding it succulent and refreshing, were soon eating eagerly (though first removing the small, pinkish snails that were crawling on the stems). Before moving on they made up bundles of stems to carry back to their shipmates.

Suddenly the clouds blew off the ridge and the sailors found themselves at the top of a sheer cliff, with a spectacular view to the southeast. Below them was an enormous valley, cradling a tiny sandy bay that offered a possible landing place though no safe anchorage. To their right was a longer vista, dominated by towering grey rocks with circling clouds of seabirds. There was no time to explore the valley, even if they could have found a way down, and they started the long trek back to the bay where they had landed, where seal meat and a variety of fish caught from the rocks was cooking over fires in a makeshift camp close to the shore.

Although the Portuguese explorers made little initial impact on the island, they left a long-lasting legacy in the form of goats and pigs. During the ensuing decades the browsing goats multiplied into vast herds and ate their way through the endemic vegetation, which had no physical or chemical defences against such an onslaught. The omnivorous pigs also devastated the seabird colonies, eating eggs, young and even adult birds. Rats arrived before the end of the sixteenth century, and may have been responsible for the extinction of the endemic landbirds whose bones have been found in the subfossil deposits.

By the time that the first settlers arrived in 1659, the island was already dramatically altered. The ecological decline continued through the subsequent centuries, in spite of sporadic efforts by the better Governors to control goats and so protect some of the native trees. What was left of the seabird colonies were destroyed by the feral dogs and especially cats that now roamed the island. We shall never know how many endemic invertebrates have been lost due to predation by introduced rodents and centipedes, agricultural pesticides and habitat destruction. Even many species which are known to have survived until the middle of the twentieth century apparently have not been able to sustain their populations in recent decades.

So, if we briefly retrace Joao da Nova's exploratory visit we shall find vast changes. The sand on the beach in Chapel Valley bay has been removed and used for building. There are no seals on the beaches and turtles have not been found breeding on the island for many years. Almost no seabirds nest on St Helena, except on offshore islets and a few cliffs where they cannot be reached by people, cats and rats. The flightless rails, cuckoo and hoopoe are all extinct, although the Wirebird has survived and flourishes in several parts of the island. The Dwarf Ebony no longer adorns the slopes of Chapel Valley, although the larger species of Ebony has been brought back from the brink of extinction and one can still find Baby's Toes, Salad Plant, St Helena Tea and Old Father Live Forever in remote places.

Large areas in the outer parts of the island have become eroded deserts, since they no longer have plant cover to protect the soil. Scrubwood is now restricted to remote rocky areas and endemic giant earwigs and giant beetles have not been seen for several decades. At higher elevations the forests of gumwoods, cabbage-trees and ferns are reduced to tiny fragments; many of the endemic beetles, snails and other invertebrates characteristic of these forests have not been seen in recent years.

However, as we said at the start, St Helena remains a beautiful and fascinating island to visit. The extraordinary geological features make visits to the coast and to other barren areas such as Prosperous Bay Plain especially rewarding, and the quiet pastoral interior is a delight to travel through. The Peaks are still home to some of the rarest plants and invertebrates in the world, and the views from the ridge and down into Sandy Bay encompass truly spectacular scenery.

St Helena's plants and animals have attracted many visiting naturalists, the most notable in this century being the zoologist Arthur Loveridge (who retired to the island), the American palaeontologist Storrs Olson, a group of entomologists from the Musée Royal de l'Afrique Centrale in Tervuren, Belgium (generally just referred to as the Belgians) and the botanist Quentin Cronk.

Our own involvement with the island began in 1959, when Philip and a colleague, who had been studying seabirds on Ascension Island, made a brief visit to St Helena and discovered bones of many of the extinct birds. During our visit in 1994-95 we were investigating the underground fauna of the island. We had previously found a number of endemic invertebrates in caves on Ascension and wanted to know whether there were comparable ones on St Helena (the quick answer is that there are very few, probably because subterranean cavities have mostly been filled up with silt during flooding).

There is now good knowledge of the remarkable native flora and fauna of St Helena, and recent years have seen the development of serious attempts at conservation of the endemic animals and plants that remain. The plight of the invertebrate endemics has been brought to public attention by initiatives of Paul Pearce-Kelly and his colleagues from London Zoo, and the recently formed St Helena Nature Conservation Group is actively promoting conservation issues among ordinary people on the island.

Government initiatives include the removal of the goats and almost all the feral donkeys that once roamed freely over the Crown Wastes. Laws have been passed to protect seabirds and dolphins, and a Sustainable Environment and Development Strategy and Action Plan for St Helena has been produced; the report of this work, coordinated by the Royal Botanic Gardens at Kew, was published in 1993.

A more recent and exciting development is the establishment in 1996 of Diana's Peak National Park. This has done much to focus attention on the remains of the unique high altitude forest. The park has an area of 64 hectares, including 15.7 hectares of tree-fern thicket. The encroachment of New Zealand Flax (cultivated earlier in the 20th century but now abandoned) is being tackled and trials are being carried out to see which is the best way of recreating tree-fern thicket on areas that have previously been flax plantation; other invasive alien plants are also being weeded out.

Practical work on conservation of the native trees has been carried out by the Endemic Section of the Department of Agriculture & Forestry, led until 1995 by George Benjamin, a St Helenian who has devoted much of his life to the survival of the endemic flora. Native trees have been propagated and planted out in the wild in several areas, and seed nurseries for over a dozen endangered endemic plants have recently been established. Furthermore, a serious threat to the survival of the Gumwood seems to have been averted. Early in the 1990s the main natural stand of Gumwoods, at Peak Dale, was facing destruction as a result of attack by an introduced homopteran insect, Orthezia insignis (locally known as the Jacaranda Bug); biological control was initiated promptly and saved most of the trees.

Apart from the necessary desperate measures to avoid more extinctions, several ambitious schemes have been suggested to restore some of the original communities of the island. We are impressed by Quentin Cronk's idea that a more extensive National Park should be established encompassing the whole of the wild southwest corner of the island from Peak Dale down to the coast between Sandy Bay and South West Point (but excluding private land and grazing areas). This area amounts to more than one tenth of the surface of the island and could become the site of an ecological restoration project on a scale sufficient to gain international recognition and support. The area is of no economic value, has relatively few invasive alien plants and has surviving populations of most of the endemic plants (and probably animals) typical of the drier zone. Over the long term it might be possible to recreate approximations to most of the original vegetation zones of the island.

Another idea is to try to bring back seabirds to some parts of the main island, by protecting them from feral cats. Turtle conservation is also an important issue, treated as a high priority in many parts of the world (including Ascension Island) but not often considered on St Helena. It is highly probable that a breeding colony of Green Turtles could be re-established, if the females could be given access to a soft sandy beach and be protected from disturbance - not easy on an island where almost all the sandy beaches have disappeared.

Since the "Earth Summit" at Rio in 1992, states have accepted an obligation to protect the biodiversity of their natural environments, and concern about the destruction of wildlife is relatively high on the political agenda. With many conservation projects already in progress and others under consideration, there is now perhaps more activity relating to conservation on St Helena than at any time in its history.

We feel bound to emphasize, however, that rising awareness and activity do not automatically lead to achievement in the long run. Sustained interest and action is essential, and our survey of the history of conservation efforts on St Helena has shown that it is continuity of effort that is often lacking. If St Helena is to preserve her unique habitats and endemic plants and animals, and again become an island welcoming turtles and a variety of seabirds, the impressive recent initiatives must be adequately supported and carried forward into the next millennium.