Vegetation of the Society Islands

Abstract

The vegetation of the Society Islands, 16°-18° south of the equator, in the wet SE trade wind belt, is described. The flora is primarily of Indo-Malayan derivation with a few New Zealand, Australian, American, and Hawaiian elements. There is little doubt that the volcanic islands at the time of human arrival, perhaps 4000 yr ago, were forested from mountaintop to seashore. The original vegetation consisted of broad-leaved, usually hygrophilous, montane rainforest. There was an abundance of shrub and small tree species, and terrestrial ferns dominated the ground layer. The sequence of vegetation from forest on the coastal zone and in deep valley bottoms through montane rainforest, mossy or cloud forest, and mossy scrub-covered crests and peaks is distinguished. With the arrival of the Polynesians, nonindigenous plant species were introduced for food, medicine, and fiber,and "camp followers" arrived accidentally. Native species, especially in the lowland coastal zone, were replaced with coconut groves; taro marshes; and valley-bottom forests of mape, breadfruit, and bamboo. The advent of Europeans brought further, often disastrous, change as newly introduced goats and pigs and logging and clearing opened up originally closed formations. Exotic species such as mango and guava came to dominate the vegetation in some places. The flora of the five atolls and the barrier-reef islets is essentially that of strand habitats throughout the Indo-Pacific and is impoverished. There was a mixed broad-leaved forest of several common widespread strand species such as Pisonia, Guettarda, Pandanus, etc., and the halophytic Tournefortia and Scaevola toward the seaward periphery. The original vegetation has also been changed by human activity, replaced by coconut and breadfruit groves and, in wet places, by taro pits. The vegetation patterns of the individual islands are also described.