Woody Vegetation on the Raised Coral Limestone of Mangaia, Southern Cook Islands

Abstract

Mangaia, the second largest (51.8 km2 ) of the Cook Islands, has a central, volcanic region with a maximum elevation of 169 m above sea level. The igneous interior is surrounded by an extensive formation of elevated coral limestone as much as 2 km wide and 70 m above sea level. Although the native vegetation in the volcanic interior has been altered greatly through human interference, a quantitative survey in the raised limestone region indicates that plant life on the elevated reefs is still largely dominated by native species. Seventy percent of the woody species recorded in 20 transects are either indigenous or endemic to the Cook Islands, and native plants accounted for 88% of the total basal area covered by the woody vegetation sampled on the raised coral limestone. Herbaceous ground cover in the study area was almost completely dominated by native species (99%). Four woody plant associations in the limestone areas are recognized by dendrogram analysis: (I) mixed native forest, dominated by Elaeocarpus tonganus; (2) disturbed mixed native forest, dominated by Hernandia moerenhoutiana or Cocos nucifera; (3) Pandanus scrub; and (4) Barringtonia forest. Some biogeographical aspects of the relatively undisturbed limestone forest region and the ecological implications of human disturbance of the vegetation on Mangaia are also discussed.