Restricted plant species on sub-Antarctic Macquarie and Heard Islands

Abstract

The recent distributional history of two Macquarie Island vascular plant species, Carex trifida, Poa litorosa, and the Heard Island vascular plant, Ranunculus crassipes is examined. C. trifida is known from only one small population on the north west coast of Macquarie Island. Four populations of P. litorosa were first recorded in the 1980s; we believe however, that it was first observed, but misidentified in the 1950s. R. crassipes was first discovered on Heard Island in the late 1980s. We argue that all three species are indigenous and arrived on their respective islands within the last 200 years by natural processes, most likely from warmer neighbouring islands, where these species have more extensive distributions. There have been small-scale changes in distribution of all species, mainly expansion. Further expansion of all three species is expected as a response to warming climate. Feral rabbit grazing is having a confounding negative influence on populations of P. litorosa.

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

“…On Campbell Island P. litorosa grows most vigorously on sites with enhanced fertility such as coastal areas, swamp flushes and near wildlife colonies, while in upland areas plants are commonly smaller (Meurk et al 1994). P. litorosa is also present on Macquarie Island, the only sub-Antarctic island on which it is found (Bergstrom et al 2006), and patterns of growth appear similar to those on Campbell Island. The species was first observed on Macquarie Island by G. Copson in 1983 (P. Turner pers.…”

“…) and recorded by Seppelt et al in 1984. Between 1983and 1985 four populations of P. litorosa were documented, the largest in the north at Handspike Point near sea-level and three small higher-altitude populations at Caroline Cove Amphitheatre, Caroline Creek and Hill 291 on the southern end of the island (Bergstrom et al 2006) (fig. 1).…”

“…(contracta) which was likely to have been a misidentification of P. litorosa (Taylor 1955, Bergstrom et al 2006. Between the 1980s and 2003 various observations were made of the four populations by Bergstrom et al (2006).…”

“…Poa litorosa Cheeseman, a tall tussock grass, was first recorded on Macquarie Island in 1984 and, until recently, was known from only four small populations (Bergstrom et al 2006). Under heavy grazing, P. litorosa is difficult to distinguish from other grass species, particularly Festuca contracta Kirk (Bergstrom et al 2006).…”

“…Under heavy grazing, P. litorosa is difficult to distinguish from other grass species, particularly Festuca contracta Kirk (Bergstrom et al 2006). Over the summer of 2013/14, it was noted in several new locations.…”