Impact of Feral Herbivores on Mamane Forests of Mauna Kea, Hawaii: Bark Stripping and Diameter Class Structure

Abstract

Management of feral and Mouflon sheep and feral goats within the Mauna Kea Forest Reserve/Game Management area has been criticized as inadequate to prevent the adverse environmental impact which these introduced herbivores have on native components of the scrub forest ecosystem. This study determined the intensity of bark stripping of mamane (Sophora chrysophylla), a small endemic leguminous tree, by these animals and assessed the impact of their browsing on the size class structure of mamane stands. In all but one of the 4 areas sampled, a high proportion of mamane trees bore bark stripping wounds. Differences in the amount of stripping between elevations in a given area, and between areas, were attributed to differences in browsing pressure, which in turn was dependent on the frequency of human disturbance and the behavioral traits of the herbivores. Tree size class distributions revealed that browsing has suppressed mamane reproduction in some areas. Suppression appeared to be the greatest in the most heavily browsed areas.