The impact of browsing on wilding conifers in the South Island high country

Authors: Nick J. Ledgard, David A. Norton
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2007, Issue N.Z.J.For. 52(4) 2008, pp 29-34, Jan 2008
Publisher: New Zealand Institute of Forestry

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Abstract: Browsing by domestic and wild animals is likely to have a major influence on the survival of young seedlings of wilding conifers in the South Island high country. But to be successful wildings must be browsed before they reach 2 years of age after which they become sufficiently woody and robust to make it difficult for animals to cause complete defoliation, and hence mortality. Palatability to browsing animals varies with species, with Corsican pine (Pinus nigra) being the least preferred. Sheep are more effective in suppressing wildings than cattle. Low grazing pressures of >0.5 sheep stock units/ha can have a significant impact on seedling establishment and early growth rates, particularly where seed rains are light. The use of fertilisers can increase grazing levels and hence wilding control. The impact of wild animals is variable. Rabbits are generally more effective than possums or ungulates, and the consequences of improved rabbit control after the 1940s and the arrival of rabbit haemorrhagic disease in 1997 have almost certainly led to higher wilding numbers. Although wilding control can be enhanced by increasing browsing levels, perhaps aided by fertiliser application, both can impact negatively on native conservation values by promoting the grazing of native plants and their suppression by the enhanced vigour of competitive exotic grasses. Two case studies at Mt Dewar and Flock Hill Stations show how changes in farm animal stocking levels have led directly, although inadvertently, to increased wilding numbers. The opportunities for wilding spread can be expected to increase as sheep populations continue to decline, wild animal control improves, and tenure review leads to formerly grazed land being retired into the public conservation estate. There is a case for the more strategic deployment of browsing to control wildings, but this must be used with due consideration of potential adverse impacts on other values.

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