Impacts of nonnative ungulates on ecosystem structure and function in Hawaiian forests

Figure 4a. Nonnative feral pigs degrade native wet forests in Hawai‘i via rooting and mixing of soil horizons, trampling and consumption of native plants, and transport of nonnative seeds (Photo Credit: Hawaii Volcanoes National Park).

Hawaiian  forest ecosystems are currently undergoing rapid degradation as a result of nonnative feral ungulates, with implications for forest composition, structure, and biogeochemistry. For example, feral pigs disturb soil via rooting and mixing of soil horizons, and plant communities via the trampling and consumption of native plants and transport of nonnative seeds. We are examining how dominant nonnative ungulates, and their subsequent removal, alters ecosystem structure and function in native Hawaiian wet and dry forest ecosystems. Our current work is focused on: (1) understanding native and nonnative plant community dynamics in the presence of nonnative ungulates, and following their removal;  (2) examining the biogeochemical impacts of nonnative ungulates in these forests, and the response to their removal; and (3) testing management strategies to improve native vegetation following nonnative ungulate removal. This work has been funded by the USDA-CSREES-TSTAR Pacific Program, the DoD Strategic Environmental Research and Development Program (SERDP), and the  College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa.

Publications to Date

Wehr NH, Hess S, Litton CM (In Press) Biology and impacts of Pacific Island invasive species. Sus scrofa, the Feral Pig (Artiodactyla: Suidae). Pacific Science.

Long MS, Litton CM, Giardina CP, Deenik J, Cole RJ, Sparks JP (2017) Impact of nonnative feral pig removal on soil structure and nutrient availability in Hawaiian tropical montane wet forests. Biological Invasions, 19, 749-763. (PDF)

Evans EW, Ellsworth LM, Litton CM (2015) Impact of grazing on fine fuels and potential wildfire behavior in a non-native tropical grassland. Pacific Conservation Biology, 21, 126-132. (PDF)

Cole RJ, Litton CM (2014) Vegetation response to removal of non-native feral pigs from Hawaiian tropical montane wet forest. Biological Invasions, 16, 125-140. (PDF)

Murphy MJ, Inman-Narahari F, Ostertag R, Litton CM (2014) Invasive feral pigs impact native tree ferns and woody seedlings in Hawaiian forest. Biological Invasions, 16, 63-71. (PDF)

Chynoweth MW, Litton CM, Lepczyk CA, Hess SC, Cordell S (2013) Biology and impacts of Pacific Island invasive species. 9. Capra hircus, the feral goat (Mammalia: Bovidae). Pacific Science 67: 141-156. (PDF)

Cole RJ, Litton CM, Koontz MJ, Loh RK (2012) Vegetation recovery 16 years after feral pig removal from a wet Hawaiian forest. Biotropica, 44, 463-471. (PDF)

Dunkell DO, Bruland GL, Evensen CI, Litton CM (2011) Runoff, sediment transport, and effects of feral pig (Sus scrofa) exclusion in a forested Hawaiian watershed. Pacific Science, 65, 175-194. (PDF)

Figure 4b. Feral pig damage in native wet forests on the Island of Hawai‘i. This fence-line photo, taken only six months after the construction of a pig-proof fence, demonstrates pig disturbance to the soil surface. The left-side of the image (where pigs are still present) has almost no litter layer and limited plant establishment, while the right-side of the image (where pigs have been excluded) has an intact litter layer and abundant native forest regeneration.