Impacts of Hurricane Iniki on Koa Forests

On 11 September 1992, Hurricane Iniki struck koa forests we had studied along an elevation gradient (500 to 1300 m) on western Kaua'i. The hurricane decreased canopy leaf area by 29 to 80 percent, and damage was proportional to pre-hurricane leaf area and canopy height. At some sites, phyllodes were stripped from intact branches, leaving the canopy otherwise intact. At other sites, many large branches and a few entire trees were broken off, thereby removing most of the overstory canopy. The canopy damage resulted in a large pulse of litter, ranging from 4 to 19 t ha' across our study sites. In the first six months following the hurricane, tree growth rates decreased in proportion to leaf area lost. Thereafter, growth rates increased, generally following the pattern of leaf area recovery. Survival of severely damaged koa trees (losing more than 75 percent of their crowns) ranged from zero to 80 percent, and was higher at wetter sites. Koa seedling densities were highest at mid-elevation sites as a result of both high emergence and high survival. Seedling densities were lower at sites with greater amounts of hurricaneinduced litter. The alien species guava (Psidium guajava) generally had higher survival than the native 'a'ali'i (Dodonea viscosa), both as adults and as seedlings, but there was relatively little invasion of alien species following the hurricane. At these sites, there was no drastic change in species composition following hurricane disturbance, and forest structure and productivity had recovered to a great degree within two years.