The influence of feral goats on koa (Acacia koa Gray) reproduction in Hawai`i Volcanoes National Park

Spatz, Gunter; Mueller-Dombois, Dieter

Goats were introduced to the Hawaiian Islands nearly 200 years ago. They have become wild and today roam in many Hatlaiian ecosystems with dry-season climates from the lowlands to the mountains. A q u a n t i t a t i v e analysis was made to evaluate the influence of f e r a l goats on tree reproduction of Acacia ko- i n the mountain parkland ecosystem on the east flank of Mauna Loa. In - t h i s ecosystem, the endemic koa is the only important t r e e species. Here it reproduces vegetatively from root suckers. Suckering has resulted in the formation of small, dense t r e e colonies. Ten transects were established through a goat exclosure t h a t was constructed three years e a r l i e r (in 1968). In addition, s i x transects were run a c r o s s s e v e r a l typical nonfenced koa colcnies. A l l suckers were counted, measured for height and mapped. It was shown that kos reproduction below 10 cm height is abundant outside the exclosure and a t the unfenced colonies. Almost t o t a l l y missing a r e suckers between 0.5 m and 2 m height. However, hundreds of t h i s height grow inside the goat exclosure. Most of the few t r e e s of t h i s height found outside the fenced area were dying or dead showing that the current goat pressure i s so high that the reproduction cycle of ko- i s nearly disrupted. The dense and vigo--ous sucker growth inside the exclosure, which is the r e s u l t of current release f r o s goat browsing pressure, was found t o be an a r t i f a c t . The a r t i f a c t has resulted frcn increased suckering density caused bg goat feedinn and probably trampling on shallow roots, Thus, the e n t i r e f o r e s t stand structure i n the mountain parkland i s d i r e c t l y related t o herbivore feeding and departs d e f i n i t e l y in spacing and probably i n height growth from the o r i g i n a l f o r e s t s t r u c t u r e as evolved during island ecosystem evolution.