Reproduction of Acacia koa after Fire

Abstract

The abundance, distribution, growth, and mortality of koa (Acacia koa Gray) seedlings after fires were monitored periodically on two burned areas on Oahu for 2.5 years. On one area, seedling density peaked at 95,300/ha 6 months after the fire; 21 months later it had declined to 18,500/ha. On the other area, peak seedling density occurred at 2 months, with 20,400/ha; 26 months later, density had dropped to 7900/ha. Seedlings were not distributed uniformly over the burned areas but were concentrated near koa seed trees. Height growth for seedlings on one area averaged 2.6 cm/mo; on the other, 1.9 cm/mo. Several pathogens were identified, but only the root-crown fungus, Calonectria crotalariae, caused serious damage. More than 50 percent of the mortality on one burn was attributed to it. The regeneration in the burned areas studied indicates that koa will continue to be a component of the forest vegetation.