Vegetation and Flora of Pitcairn Islands

The Pitcairn Islands are a remote group of four islands, roughly half way across the southern Pacific Ocean between Australia and Chile, on the tropic of Capricorn.

The North Beach of Henderson Island. The raised atoll of Henderson has many endemic plants and animals. Unlike many other raised atolls, Henderson has not been exploited for rock phosphate, and despite a period of Polynesian colonisation, it has very few non-native plants. These factors, together with its many endemic plants and animals, mean that the island is virtually unique and hence irreplaceable- hence its status as a World Heritage Site.

Henderson, with four endemic landbirds, nine endemic higher plants and almost no non-native plant species, has been designated a World heritage site for its unique biota.

One of the endemic higher plants of Henderson, Ixora fragrans is, as its name suggests, an attractive highly scented species. It forms dense thickets on the plateau of the island. Ixora species have interesting pollen presentation- the pollen is released from the anthers onto the style, but away from the stigmatic surfaces, before the flowers open.

Santalum insulare var. hendersonense is one of nine endemic higher plants from Henderson. Similar sandalwood species have been over-exploited elsewhere in the Pacific, but the remoteness of the Pitcairn group has ensured the survival of the Henderson taxon.

However, Pitcairn Island is perhaps better known, being the island colonised by the Bounty mutineers. There are two uninhabited atolls, Oeno and Ducie, and the four islands are administered as British Overseas Territories. The Department's involvement in the flora of the Pitcairn Group began when Steve Waldren spent three months in the Pitcairn group in 1991, based mostly on the uninhabited Henderson, but some time was also spent on Oeno and Pitcairn.

A view across Rope Bay on Pitcairn. Pitcairn is a small island almost completely surrounded by cliffs; remarkably there is a rather hair-raising path and rope down the vertical cliff at 'Down Rope'. Those intrepid enough to venture down will be rewarded with interesting strand line plants on one of the islands few boulder beaches, and cliff petroglyphs which recall Pitcairn's former importance as Polynesian stone tool manufacturing site. The photograph shows the lack of a fringing reef which would protect the coastline from heavy swells; even though this was a calm day the bay is still white with surf.

A subsequent visit by Steve Waldren and Naomi Kingston in 1997 concentrated more on Pitcairn, with a brief visit to Henderson. Our work has consisted of mapping the flora and vegetation communities, defining threats to native species and drawing up conservation priorities.

Metrosideros collina trees growing in montane cloud forest on Pitcairn. Even though the highest point (imaginatively named 'Highest Point') is some 320 m above sea level, the upper zones of Pitcairn are often cloud covered. The trees have abundant aerial roots and these can bee seen hanging from the branches. Old trees, such as the one shown, often grow semi-prostrate.

McCoy's Valley on Pitcairn, showing a typical patch of remnant native vegetation at moderate to high altitude. The tree canopy is dominated by Metrosideros collina, with arching or decumbent trunks richly clothed with epiphytes, while the ground flora consists of several native fern species, including the endemic Ctenitis cumingii.

Most of the threatened species occur on Pitcairn, the only island of the group currently inhabited. Major threats include the spread of invasive species, clearance of remnant forest, erosion and the genetic and demographic problems faced by critically low population numbers. We are working with the Island community and Administration to integrate much-needed development with conservation; however, recently proposed large-scale developments will pose severe threats to the biota of this remote island group.

The higher altitude forests of Pitcairn have abundant epiphyte growth, this photo shows fertile fronds of the rhizomatous fern Pyrrosia serpens. The green linear structures growing amongst the bryophytes are the photosynthetic rhizomes of a tiny leafless orchid, Taeniophyllum fasciola.

Coastal cliff vegetation on Henderson showing the flowers of Capparis cordifolia (a relative of capers), which is widespread in the Pacific islands. The other species in the view are much more restricted in their distribution. The small, rounded grey-green leaves are those of Chamaesyce sparrmannii which is restricted to the Pitcairn group and Marotiri Rocks off Rapa; the lighter green leaves are those of Senecio stokesii, which occurs only on Henderson, Rapa and some of the Austral Islands. The latter species demonstrate the close phytogeographical links between the Pitcairn group and the Austral/Rapa group of islands.

Hibiscus australensis, first collected from Pitcairn in 1997. Elsewhere, the species occurs in the Austral islands and is another example of the close phytogeographic link between the Pitcairn group and the Austral/Rapa group.