Woody Vegetation in the Upland Region of Rarotonga, Cook Islands

Abstract

Rarotonga is the largest (64 km2 ) and by far the highest (652 m) of the Cook Islands. The native coastal and lowland vegetation of this high volcanic, tropical island has been either completely removed or heavily disturbed. Numerous exotic plant species have been introduced and many of these are now naturalized in the lower elevation habitats of the island. The results of this initial, quantitative study in the upland forests of Rarotonga indicate, however, that the plant life of the rugged interior is still largely dominated by native species. Over 92 percent of all the woody plants (dbh > 2.5 cm) sampled in the 19 upland forest transects are either indigenous or endemic to Rarotonga. Native plants also accounted for more than 95 percent of the basal area covered by the woody vegetation in the upland study area. Three basic native plant associations have been recognized by dendrogram analysis: (1) the Homalium montane forest; (2) the Fagraea-Fitchia ridge forest; and (3) the Metrosideros cloud forest. The first two associations develop under subtropical climatic conditions, while the cloud forest is adapted to warm temperate conditions. Some aspects of the biogeographical significance of this unique forest region and the ecological implications of human disturbance in the uplands are also discussed.