The non-native vascular plants of Henderson Island, South Central Ocean

Résumé

Henderson island, a World Heritage Site in the Pitcairn group, south-central Pacific Ocean, has often been thought to have a pristine vegetation. Our archaeological investigations and field observations in 1991-1992, supported by recent observations in 1997, suggest the occurrence of former areas of Polynesian cultivation near to the North and East Beaches, and indicate that about 17 non-native vascular plant taxa have occurred. The majority of these were deliberate Polynesian introductions, some taxa are known only as sub-fossils from Polynesian occupation sites; some of this sub-fossil material may represent imported plant parts such as timber or food wraps, rather than indicating in situ cultivation. These Polynesian introductions show little spread from their probable site of introduction and are mostly restricted to the vicinity of the northern beaches; some have become extinct on Henderson. The Pitcairn islanders have also introduced a small number of vascular plants, and one of these (Passiflora maliformis) is potentially invasive. Other taxa have been accidentally introduced, at least one by a recent scientific expedition in 1991. The intact nature of much of the native vegetation may have restricted the opportunities for more widespread colonization; care is needed to ensure that this situation persists.