Vegetation Changes Induced over 10 Years by Goats and Pigs at Port Ross, Auckland Islands (Sub-Antarctic)

Marked sites established around Port Ross in 1973 were re-examined in 1983 to measure changes in the vegetation and assess the impact of goats and pigs. Goats had not increased in numbers, nor extended beyond their earlier range, but they were seen higher on the Hooker Hills. Pigs were scarce, but their sign was seen throughout. Photopoints and numerical methods both showed that Chionochloa antarctica tussock was eliminated or greatly reduced where goats and pigs occurred together, and where only pigs were present it was reduced slightly. Despite browsing by goats, woody vegetation has continued to replace the Chionochloa tussock grassland and occupy sites where tussock has been removed. Poalito rosa tussock has further invaded a strip of dead Hebe elliptica-Metrosideros umbellata forest killed by goats and by exposure to the wind.
As the low-altitude Chionochloa tussock disappears, goats may move to unmodified tussock grassland at higher altitudes and so gain access to other parts of the island. Pigs, by rooting and browsing, will continue to reduce lowland Chionochloa in their range. Extermination of pigs and goats from the main Auckland Island should therefore be planned.