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Feral pigs in a temperate rainforest ecosystem: disturbance and ecological impacts

Abstract

Feral pigs (Sus scrofa) are a widespread invasive species, and cause biotic disturbance. This study evaluated the impacts associated with ground disturbance by feral pigs in the North Island of New Zealand. Exclosure cages were erected over feral pig-disturbed ground and visually undisturbed ground (the latter as controls). Buried resin bags and litter bags were located in these plots to examine differences in soil nutrients and decomposition rates and seedling/sapling recruitment (abundance, species composition and richness) was monitored over 21 months. No difference was found in the litter decomposition between the disturbed and visually undisturbed plots. Significantly more nitrate (NO3-N/NO2-N) was found in the disturbed exclosures. Seedling density was not significantly affected by feral pig disturbance. However, seedling/sapling species richness was lower in disturbed areas. Species composition changes occurred at disturbed sites with species increasing and decreasing in density after feral pig disturbance. However, no pattern was observed between species that were negatively affected by feral pig disturbance. This study shows that feral pig disturbance affects vegetation through direct removal, but also indirectly through increased nitrate, potentially leading to seedling and sapling species composition changes. Feral pigs are known to return to previously disturbed areas to re-disturb. These areas may remain in a re-disturbed state if not protected, and through continued disturbance and increased nitrate, ecosystem changes may occur, especially in characteristically nutrient poor environments.

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Acknowledgments

We would like to thank Auckland Council, Landcare Research and the University of Auckland for funding and to Auckland Council for permits to conduct this study. We are grateful to a number of researchers and technicians who helped with this study; S. Anderson, K. Booth, T. Dutton (and lab), A. Evans, N. Falxa-Raymond, E. Feenstra, P. Goldsmith, D. Krull, S. Large, C. Miner-Williams, L. Miner-Williams, C. Sheppard, A. Tomlinson, C. Warner and M. Wheat. We also thank a number of Auckland Council staff, J. Brooks, H. Cox, J. Craw, A. Davis, M. Geaney, N. Leuschner, G. McCarthy and N. Waipara. B. Lee and S. Wyse provided helpful comments on this paper and K. Ruggerio provided statistical advice and helped with analyses.

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Correspondence to Cheryl R. Krull.

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Krull, C.R., Choquenot, D., Burns, B.R. et al. Feral pigs in a temperate rainforest ecosystem: disturbance and ecological impacts. Biol Invasions 15, 2193–2204 (2013). https://doi.org/10.1007/s10530-013-0444-9

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  • DOI: https://doi.org/10.1007/s10530-013-0444-9

Keywords

  • Feral hog
  • Sus scrofa
  • Disturbance
  • Impacts
  • Exclosure
  • Regeneration