A multinational study spanning three subantarctic islands, has given us an insight into the effects of climate change on subantarctic plant species.
The three islands in the study — Marion Island, Iles Kerguelen and Heard Island — lie north, within and south of the Antarctic Polar Frontal Zone (APFZ), respectively. This zone, on the edge of the Antarctic region, is both an oceanic and climatic boundary, with warmer seas and air temperatures to the north and colder temperatures to the south. The three islands therefore provide a latitudinal temperature gradient and a fabulous suite of natural laboratories to explore the impact of temperature on species’ performance and ecosystem structure.
There is about a 2°C jump in average air temperature between each island, starting with Heard in the south at about 1.5°C; 3.5°C on Kerguelen; and 5.5 °C on Marion. This natural temperature gradient provides a useful analogy for the impact of climate change, with the warmer islands being models of what the cooler islands will be like in the future.
To overcome problems with year-to-year variations in seasonal temperatures — a hot summer one year and a cold summer the next, for example — we deployed teams on the three islands simultaneously over the 2003–04 summer. Logistical support was provided by Australia, France and South Africa, while scientists from eight nations were involved, either in the field or patiently awaiting samples.
There were many components to the three islands study, but one of the main ones involved examining the differences in the progression of flowering and seed development in four important plant species that occur on all three islands. These were the Kerguelen cabbage, Pringlea antiscorbutica, which is endemic to these islands as well as Iles Crozet; the cushion plant, Azorella selago; a subantarctic tussock grass, Poa cookii; and a creeping, wiry subantarctic herb from the rose family, Acaena magellanica. We had sites established along altitudinal gradients on all islands and these sites were visited every five days, weather permitting. Plants, identified by temporary markers, were monitored throughout the summer.
Our preliminary analysis has shown that not all species perform in the same way across the temperature gradient between the islands. This is important because it give us clues as to whether or not there will be winners and losers in a climate change scenario. Although we expected a lag in flowering development on the colder islands, compared to the warmer islands, in the case of Acaena magellanica, development differed by more than one month between Kerguelen and Heard islands. Such a lag time was surprising. Furthermore, coastal Acaena on Kerguelen had three flushes of flowers, compared to only one on Heard. The end result of this behaviour was substantially more seed production on Iles Kerguelen compared with Heard Island by the end of summer, so that Acaena may be more competitive under warmer conditions.
The three islands study was part of an international Scientific Committee on Antarctic Research program called RiSCC (Regional Sensitivity to Climate change in Antarctica) and took advantage of the opportunity that co-operation between nations in the Antarctic offers. Support for the visit to Kerguelen came from both the French Antarctic program and the French Embassy in Australia.
Adaptation to Environmental Change Program,
Australian Antarctic Division