Acacia koa for up to 25 years. Scarification is needed before "A. koa" seeds will germinate. Koa is endemic to the islands of Hawaii, Molokai, Maui, Lānai, Oahu, and Kauai, where it grows at elevations of . It requires of annual rainfall. Acidic to neutral soils (pH of 4-7.4) that are either an Inceptisol derived from volcanic ash or a well-drained histosol are preferred. Its ability to fix nitrogen allows it to grow in very young volcanic soils. Koa and ōhia lehua ("Metrosideros polymorpha") dominate the canopy of mixed mesic forests. It is also common in wet forests. The koa's trunk was
Hawaiian tropical dry forests Hawaiian tropical dry forests The Hawaiian tropical dry forests are a tropical dry broadleaf forest ecoregion in the Hawaiian Islands. They cover an area of on the leeward side of the main islands and the summits of Niihau and Kahoolawe. These forests are either seasonal or sclerophyllous. Annual rainfall is less than and may be as low as ; the rainy season lasts from November to March. Dominant tree species include koa ("Acacia koa"), koaia ("A. koaia"), akoko ("Euphorbia" spp.), ōhia lehua ("Metrosideros polymorpha"), lonomea ("Sapindus oahuensis"), māmane ("Sophora chrysophylla"), loulu ("Pritchardia" spp.), lama ("Diospyros sandwicensis"), olopua ("Nestegis sandwicensis"), wiliwili