Feral goats (Capra hircus L.) in the Macleay River gorge system, north-eastern New South Wales, Australia. I. Impacts on soil erosion
Paul Bayne A C , Robert Harden A and Ian Davies BA NSW National Parks and Wildlife Service, c/- Zoology, University of New England, Armidale, NSW 2351, Australia.
B School of Mathematics, Statistics and Computer Science, University of New England, Armidale, NSW 2351, Australia.
C Corresponding author. Present address: 140 Mt Mitchell Rd, Armidale, NSW 2350, Australia.
Wildlife Research 31(5) 519-525 https://doi.org/10.1071/WR03039
Submitted: 16 May 2003 Accepted: 28 November 2003 Published: 13 December 2004
Abstract
The impact of feral goats (Capra hircus) on the rate of erosion in steep gorge country was estimated. The erosion (sediment flux) in a manipulated treatment area before and after the removal of goats was compared with erosion in two adjacent unmanipulated areas: one with goats at high density (~20 goats km–2) and one with very few goats (~0.2 goats km–2). Erosion was measured with 36 2-m-wide catch fences, collecting debris (soil and rock) moving down 40° slopes over 10 collection periods spanning 31 months. In the central manipulated area, goats were initially at high density but were completely removed during the third collection period.
Over the 10 collection periods, erosion was consistently greater in the area with many goats than in the area with few goats (mean five times greater, range 2.4–11.8). This difference was significant for 6 of the 10 collection periods. Before goats were removed from the manipulated treatment, the erosion in this area was not significantly different from that in the area with many goats, but was significantly greater than the area with few goats. After goat removal erosion in the manipulated area decreased relative to each of the other treatments. By the final collection period erosion in the manipulated (goats removed) area was significantly less than in the area with many goats, but not significantly different from the area with few goats.
Initial reduction in erosion following goat removal was rapid, followed by a continued slower decline over the next two years coincident with a relative increase in ground-cover vegetation. It was thought that both direct physical disturbance by the goats and secondary effects due to goat impacts on the substrate and ground-cover vegetation contributed to the increase in erosion associated with the presence of goats.
Acknowledgments
Our sincere thanks go to all those involved in this project: the land holders who gave access, Shane and Sheryl Andrews, Cliff and Helen Faint, Mike and Helen Saunders, Alan and Lee Waters and New England Antimony Mines; Michael Smart and Peter Higgs for assistance with carrying rocks, and Michael for fence construction; Ken Pines and NPWS Armidale District Office for assistance with goat removal; and Richard Faulkner, Bruce Whann, Dan Alter, the Department of Environmental Engineering, and the Department of Agronomy and Soil Science at the University of New England for access to laboratories and equipment. Thanks also to Tony Auld, Gerhard Körtner, Stuart Cairns and Richard Kingsford for helpful comments and advice and to Gerhard for assistance with figures.
The research was undertaken under NSW National Parks and Wildlife Service Scientific Investigation Licences A60 and B1655 and Animal Care and Ethics Committee Animal Research Authority #44. Goat removal was undertaken in accordance with the protocols and procedures of the Feral Animal Aerial Shooting Training program (Anon. 1994) and the Australian Agricultural Council (Anon. 1991).
Abdel-Madid, A. H. , Trlica, M. J. , and Hart, R. H. (1987). Soil and vegetation responses to simulated trampling. Journal of Range Management 40, 303–306.
Bayne, P. , Harden, R. H. , Pines, K. , and Taylor, U. (2000). Controlling feral goats by shooting from a helicopter with and without the assistance of ground-based spotters. Wildlife Research 27, 517–523.
Larson, W. E. , Lindstrom, M. J. , and Schumacher, T. E. (1997). The role of severe storms in soil erosion: a problem needing consideration. Journal of Soil and Water Conservation 52, 90–95.
Pickard, J. (1976). The effect of feral goats on the vegetation of Lord Howe Island. Australian Journal of Ecology 1, 103–114.
Yocum, C. F. (1967). Ecology of feral goats in Haleakala National Park, Maui, Hawaii. American Midland Naturalist 77, 418–452.