Effects of Ungulate Management on Vegetation at Hakalau Forest National Wildlife Refuge, Hawai?i Island

Abstract

We compiled and analysed data from 1987?2004 on vegetation monitoring during feral ungulate management at Hakalau Forest National Wildlife Refuge, a tropical montane rainforest on the island of Hawai?i. All areas in the study had previously been used by ungulates, but cattle (Bos taurus) were removed and feral pig (Sus scrofa) populations were reduced during the study period. We monitored six line-intercept transects, three in previously high ungulate use areas and three in previously low ungulate use areas. We measured nine cover categories with the line-intercept method: native ferns; native woody plants; bryophytes; lichens; alien grasses; alien herbs; litter; exposed soil; and coarse woody debris. Vegetation surveys were repeated four times over a 16-year period. Vegetation monitoring revealed a strong increase in native fern cover and slight decreases in cover of bryophytes and exposed soil. Mean cover of native plants was generally higher in locations that were formerly lightly grazed, while alien grass and herb cover was generally higher in areas that were heavily grazed, although these effects were not statistically significant. These responses may represent early seral processes in forest regeneration following the reduction of feral ungulate populations. In contrast to many other Hawaiian forests which have become invaded by alien grasses and herbs after ungulate removal, HFNWR has not experienced this effect.