Abstract
Conservation and restoration of ecosystems impacted by nonnative ungulates increasingly involves their removal and exclusion. While the influence of nonnative ungulate removal on plant communities is commonly monitored, impacts on underlying ecological processes are seldom quantified. Here we examined how nonnative feral pig (Sus scrofa) removal from Hawaiian tropical montane wet forests affects soil physical and chemical properties. Unique to this study, measurements were taken in paired sites inside and outside of five feral pig removal units representing a ~20 year, highly constrained chronosequence where other potentially confounding variables are held constant. Additional targeted measurements were taken inside and outside of a single exclosure in areas characterized by ‘low’ versus ‘high’ feral pig activity. Overall, nonnative feral pig removal increased stable soil aggregates and porosity, and decreased bulk density, water-filled pore space, and soil moisture content. Further, feral pig removal increased soil nutrient regeneration as evidenced by increased extractable cations, increased resin available NO3 − and total inorganic N, and enriched foliar δ15N. Increasing time since feral pig removal was positively related to net nitrification and total net inorganic N mineralization, and negatively related to pH and net ammonification. Results from both the chronosequence and targeted sampling were consistent in direction and support a central role of feral pig removal in modifying soil physical and chemical properties. Changes in soil properties following ungulate removal coincided with large increases in understory vegetation cover, highlighting the need to better understand aboveground-belowground linkages following nonnative ungulate removal.








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Acknowledgements
Funding was provided by the College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa via the USDA-NIFA Tropical and Subtropical Agriculture Research (TSTAR) (2009-34135-20101 to CML), Hatch (HAW00132H and HAW01127H to CML), and McIntire Stennis (HAW00188M and HAW01123M to CML) programs; the Department of Defense Strategic Environmental Research and Development Program (RC-2433 to CML, JPS, RJC and CPG); and the USDA Forest Service, Pacific Southwest Research Station (to CPG). We thank Hawaii Volcanoes National Park and the State of Hawaii Department of Land and Natural Resources, Division of Forestry and Wildlife, Natural Areas Reserve System for access to field sites. We thank J.B. Friday for access to laboratory space and logistical support; N. Friday, M. Johansen, and I. Ito from the University of Hawaii Pacific Internship Programs for Exploring Sciences for tireless field and laboratory work; and A. Taylor, K. Gerow, P. Selmants, and R. Camp for advice on statistical analyses.
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Long, M.S., Litton, C.M., Giardina, C.P. et al. Impact of nonnative feral pig removal on soil structure and nutrient availability in Hawaiian tropical montane wet forests. Biol Invasions 19, 749–763 (2017). https://doi.org/10.1007/s10530-017-1368-6
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DOI: https://doi.org/10.1007/s10530-017-1368-6