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.