Rain forest establishment and succession in the Hawaiian Islands

Abstract

Processes of biological invasion, establishment and succession of tropical rain forest vegetation in the biogeographically remote insular environments of Hawaii are reviewed with reference to similarities in the ecology of post-mining landscapes. New cinder cones in volcanically active areas are completely abiotic deposits like mine spoils. Colonization can be slower than on other volcanic deposits in the same area because of fewer favorable microhabitats. Also the rate of invasion may suddenly increase if a native dispersal agent reappears in the recovery process. Over longer time spans the successional pathways converge, overriding the initial substrate differences. From Hawaii’s naturally impoverished, native biodiversity, a simple monodominant rain forest emerges, which is dominated by a pioneer tree species, Metrosideros polymorpha (Myrtaceae). This species appears as the first tree on raw volcanic substrates and maintains its dominant canopy position by a growth cycle involving canopy dieback. It, thereby, creates secondary successions favorable for its own regeneration as a shade-intolerant pioneer tree. A long-term succession model shows progressive development terminating in a plant biomass and biophilic nutrient climax. This climax may last for thousands of years to be followed eventually by a regressive phase. In this phase, the monodominant forest recovers with decreasing stature and biomass due to nutrient depletion. An independent soil genesis model supports this trend, which ends in the formation of nutrient exhausted volcanic soils with accumulated gibbsite in ferruginous bauxite. Metrosideros and an aluminum absorbing fern, Dicranopteris linearis, still grow on these nutrient depleted bauxite enriched soils. But when these are strip-mined to saprolite surfaces, only hardy introduced species are capable of reinvasion. The native spectrum of colonizer species appears not broad enough to cope with such new and artificially exposed surfaces. Similar relationships may limit natural recovery of mine-spoils in other regions, thereby requiring costly amendments for rehabilitation.