The ecological distribution of C₄ and C₃ grasses in the Hawaiian Islands

Nearly two-thirds of both the native and exotic grasses of the Hawaiian Islands are C₄ species. Elevational gradients on the island of Hawaii demonstrate that C₄ taxa dominate both species composition and coverage of grasses up to 1,000 m, while C₃ taxa predominate above 1,400 m. The elevational transition of dominance between the two metabolic systems is much sharper on a coverage than on a floristic composition basis. Despite the shaded characteristic of the habitat, C₄ grasses are the most important group in wet forests at intermediate elevations. The 1,400 m elevation of floristic balance between C₄ and C₃ grasses corresponds to a low monthly mean minimum temperature of approximately 9° C and a mean maximum temperature for the warmest month of about 21° C. These temperatures are considerably lower than those reported for a latitudinal point of floristic balance in North America, but similar to those indicated by other studies of elevational distributions of tropical grasses.