Studies in montane bogs of Haleakala National Park: degradation of vegetation in two montane bogs: 1982-1988

Abstract

The increase of alien herbaceous plant species and decrease of native species in two montane bogs in Haleakala National Park, Maui, Hawaiian Islands, were documented from 1982 through 1988. These two bogs, Big Bog (5.4 ha) and adjacent Mid-Camp Bog (3.0 ha) at 1650-1660 m (5400-5440 ft) elevation, comprise over half the total bog acreage of East Maui where they are also the two largest bogs. They contain relatively large populations of plant species that are otherwise rare and/or restricted in distribution, including the only known populations of the local endemic, Geranium hanaense. Feral pigs arrived into the area in the early 1970s and their heightened activity through the 1980s has caused the loss of native plant cover and invasion by alien plant species. The invasion of alien species into Carex echinata-dominated sites was much greater than at Oreobolus sites. During the six year study period, cover of alien species at Carex echinata sites increased from 6% to 30%. Meanwhile, the cover of alien species at six Oreobolus sites increased only modestly from 0.2% to 2.6%; however, Oreobolus declined by 50% (from 32% to 15% cover) with increases in bare ground and native species. Native bog species readily recolonize bare areas, but are replaced in Carex echinata communities by more aggressive alien species with repeated disturbance. Of alien species present at the study site, Holcus lanatus, Juncus planifolius, and Sacciolepis indica showed the greatest increases in cover and frequency. All major bogs within Haleakala National Park are now protected from feral pigs by exclosure fences. Without management action, feral pig rooting and the spread of alien plant species would have continued until alien species would likely have dominated the vegetation of these montane bog areas. Feral pig control and/or construction of fences is required if native plant communities are to be maintained in Hawaiian bog communities.