Abstract:
Goats (Capra hircus) are a common wild ungulate in New Zealand, inhabiting about 11% of the land area. Much of this land is managed by the Department of Conservation. Outcome objectives for sustained goat control operations on conservation land should relate directly to ecosystem health, which is the overall conservation objective, rather than goat population levels. In this study we developed and tested new sampling methods to assess more directly the response of forest understoreys to reductions in feral goat populations. We also attempted to separate goat from possum (Trichosurus vulpecula) impacts. The study included the establishment and remeasurement (after goat culling operations) of 274 forest understorey plots (5 m × 5 m) across one South Island and two North Island areas. The methods were successful in recognising recovery from goat impact, and in demonstrating the variable effects of different goat population levels on different groups of plants. Improvements in understorey condition following possum control were negligible in the absence of effective goat control, and were difficult to disentangle from goat-control effects where goat numbers were reduced. Possum impacts on understoreys need further study. The data collected provided a range of variables and indices with which to analyse goat impacts on forest understoreys. The choice of which variable or index a manager might use in any situation depends on the detail of information required and the specific conservation objectives desired for an area of natural estate.
