The Russian captain Thaddeus von Bellinghausen was unprepared for his first sight of Macquarie Island in 1820, writing in his ships log “We had imagined that the island Macquarie was covered in eternal ice and snow, like the island of Southern Georgia, as both are on the same latitude. We were therefore greatly surprised when we discovered that the island Macquarie is covered in a beautiful green…” The captain then adds “…with the exception, of course, of the stone cliffs, which are a gloomy dark colour” (McNab, Murihiku 1907 p 191). This dramatic differences of environment between Macquarie Island and South Georgia is due to their locations to the north and south, respectively, of the Antarctic Polar Frontal Zone.
In this short description, the captain had summed up the main features of Macquarie Island’s geology and plant life. The dominant vegetation on the island, its ‘beautiful green’, is tussock grass, with 4 species – 3 native and one introduced – to be found across the island The tussock grasses have been heavily impacted by rabbits, but are improving since the success of the Pest Eradication Project.
With no trees or shrubs growing on the Subantarctic island, the other large plant which would add to the green vista seen from the sea is the megaherb Macquarie Island cabbage Stilbocarpa polaris. It’s called a megaherb because although it’s not woody, like a small tree or shrub, it can grow up to 2 m high (but is usually smaller). This plant was used like cabbage by sealers and early explorers, with the root being a very good source of fresh food. The root was boiled and used in soups, or even pickled, a use which Bellinghausen was quick to take advantage of to top up his ship’s store of vegetables for their journey.
The captain’s ‘gloomy dark’ cliffs are, of course, one of the most distinctive features of Macquarie Island, showing its nature as an uplifted piece of sea floor. These cliffs abruptly separate the thin coastal fringe with its kelp, lichens and tough tussocks from the large plateau with its cushion plants and herbs, with coastal terraces delineating the steep elevations in between. The island’s plant life has adapted to these distinctive niches, with four different types of plant communities thriving on the tiny island – tussock grassland, herb field, feldmark and mire.
The encircling coastal communities are usually very rocky, and below the tide line support abundant kelp and other marine algae including the giant Antarctic Kelp. In the rich cold coastal waters of the island there are twice as many species of plants – mainly algaes – to be found as there are in the terrestrial areas (Selkirk et al.,1990). Moving up from the shoreline to the coastal terraces lichens, mosses and tall tussock grasses, mainly the hardy Poa foliosa grow along side Macquarie cabbage, surviving the salt spray and providing shelter for wildlife.
The wildlife, including elephant seals, penguins and gulls contribute to the survival of the coastal plant life with their manure, adding nitrogen to the thin soils. Prions and petrels take advantage of the cover of tussock grasses, burrowing their nests under the dense foliage to elude skua gulls and other predators. One of the three endemic plant species on Macquarie Island, the coastal grass Puccinellia macquariensis can be found on these rocky coastlines.
Short tussock grasslands can be found both on the plateau and in raised beach terraces. They are mainly home to hardy, smaller grasses that can tolerate high winds. Salt-laden winds are a constant on Macquarie Island, with plants having to adapt to the endless buffeting and sea spray. But even here, small herbs and orchids can be found.
Herb fields thrive in the more protected valleys and flats of the plateau, and in some sheltered coastal terraces. Herb fields support a variety of different plants, from small creeping herbs, to ferns and two species of orchid. One of the orchid species, previously called Nematoceras dienemum, has been found to be endemic to the island, and renamed Nematoceras dienema, to reflect its difference from the orchids found on other Subantarctic islands. Towering over these smaller herbs, the hardy Subantarctic megaherb silver leafed daisy, Pleurophyllum hookeri provides a bit of extra shelter from the wind and stabilises the soil with its spreading root system.
The plateau is home to the third of the Islands’ endemic species, the famed Cushion Plant Azorella macquariensis. This large, mat-forming plant has tiny leaves and stems which grow into wide, tightly packed circular shaped mounds, looking distinctly like large cushions. As well as the endemic Azorella macquariensis there is another species of cushion-forming plant on Macquarie Island that can be found on other Subantarctic islands. Rangers and scientists have noticed the island’s Cushion Plants have been dying back in recent years, despite the eradication of rabbits and rodents. It’s currently not known what is causing the die-back, but climate change is a primary suspect. Cushion Plants are the dominant vegetation in the feldmark communities of the island plateau.
The term feldmark has Norwegian roots, meaning ‘mountain field’. Feldmark is an important plant community on Macquarie Island, covering much of the plateau and incorporating most of the other plant communities. It is home to pockets of herb fields, patches of tussock grasses and windswept, gravelly swathes of Cushion Plants. Lichens, mosses and fungi are common in feldmark, and so are freshwater algae, which thrive in the islands lakes. The feldmark is dotted with lakes and small wetlands, which support herbs, mosses, algaes and ferns, and the only freshwater aquatic plant to be found on the island. Larger patches of ferns grow mainly in a few sheltered gullies on the eastern side of the island, taking advantage of the drainage channels from the plateau.
The wetlands of Macquarie Island are also called Mires, and range from shallow damp areas to deep peat bogs. The early sealers and explorers called these peat bogs ‘feather beds’, for the sensation of walking over them was like tramping over a soft mattress. These mires can be found on valley floors, on the plateau, and on some of the coastal terraces. The mires have rich vegetation including rushes, sedges and grasses (links). The vegetation breaks down and adds to the layers of peat, which in some places are many meters deep. These deep peat layers can give a snapshot of the plants and animals present at the time the layer was formed, and have been used to date the rate of geological uplift of the island (Selkirk et al., 1990).
So despite its isolation from any continent or other island, Macquarie Island has been colonised by a rich variety of plants. Seeds, spores and even vegetation have arrived on the wind, attached to bird’s feet, clinging to driftwood, or introduced by humans, and have either died off or adapted and thrived. The islands location at the northern edge of the Antarctic Polar Frontal Zone sees it experience the extreme weather of the Southern Ocean and Subantarctic, resulting in the evolution of a unique, resilient flora including three endemic species. It is hoped with the eradication of rabbits and rodents the plant life of Macquarie Island can return to its earlier, pre-exploration state.
But can it return an earlier equilibrium? The impacts of a changing climate are already being felt, and it is unknown what effects they may have on the plants and animals of the island. The ongoing presence of rangers and scientists on the island is hugely important for monitoring the state of the environment and any changes that are occurring. It is only though the observations of these dedicated individuals we are able to properly gauge what effects climate change is having on the island, and what it may mean for the future.