The influence of feral goats on the lowland vegetation in Hawaii Volcanoes National Park
Mueller-Dombois, Dieter; Spatz, Günter
The coastal lowland of Hawaii Volcanoes National Park, particularly its western part, is a concentration center of feral goats. Here, in a tropical seasonal climate, a widespread vegetation is an annual Eragrostis tenella grassland that occurs on lava rock substrates with thin layers of ash. Localized within this area occurs also a small area of deep-ash deposit (Puu Kaone) that is occupied by perennial introduced grass with scrub. Experimental goat displacement in form of exclosures on these two grasslands has shown that both are entirely goat-derived vegetations. The response to displacement of goats was immediate in both areas. In the annual grassland, bunchgrasses, woody chamaephytes and an endemic legume vine (Canavalia kauensis) became established within less than two years, while the annuals are fast disappearing. In the perennial grassland, Melinis minutiflora enlarged its grass mat, woody plants became more abundant and exposed soil was partially covered within a year after exclosure construction. The remarkable recovery of the endemic vine in the annual grassland shows that goat removal still holds hopes for at least a partial return of native vegetation. The effects of goats apart from their physical degradation of the lowland ecosystem has been primarily in the form of exhausting the seed supply of native plants by feeding on seedlings wherever they occurred in this territory. Total elimination of goats from this area can be expected to yield a partial return of native plants on these rockland surfaces.