Change in the distribution of the indigenous grass Poa litorosa on sub-Antarctic Macquarie Island following the eradication of rabbits.

Abstract

The recent eradication of rabbits, rats and mice from Macquarie Island has resulted in unprecedented changes to the vegetation. One unforeseen outcome is the expansion in the known distribution of the indigenous grass, Poa litorosa (L.) which was known from only four restricted populations on Macquarie Island prior to 2014. An increase in abundance of P. litorosa was observed in 2014 and so we undertook surveys to document changes in the known distribution of the species and established fixed transects in the new and previously recorded populations to monitor future changes. Monitoring of an exclosure and control plot over a 24-year period gave insights into past effects of rabbit grazing on the species. Our surveys documented a dramatic increase in the known distribution of the species. Existing populations have expanded and new populations have been recorded. Monitoring of the exclosure and control plot revealed suppression of P. litorosa plants in control plots in comparison to fenced plots during peak rabbit numbers, and so we attribute the population expansion to the recent eradication of rabbits and subsequent release of grazing pressure. This research contributes to the increasing bank of knowledge of changes occurring on Macquarie Island post-eradication and highlights the importance of monitoring to detect unforeseen changes.