Coastal Slopes vegetation on Macquarie Island
Scientists studying vegetation at Waterfall Bay
| The coastal slopes sharply rise 100-350m up from the surrounding beaches or raised coastal terraces to the plateau uplands of the island. Peat soils vary in depth from 30cm to over 1m deep. This area supports a range of different plant communities.
The composition and structure of plant communities in this region are primarily determined by factors relating to animal disturbance and the movement of soil, whether through soil creep or landslips. Additional factors include moisture availability and exposure to wind.
Several types of plant associations occur within this region. Much of this area is covered by a tall tussock grassland dominated by Stilbocarpa polaris and Poa foliosa. These plants form a dense, closed canopy up to 1m in height, so few other plants are able to grow amongst them.
At higher altitudes, the tall tussock grassland gives way to short grassland dominated by Luzula crinita and Agrostis magellanica.
Also found in the coastal slopes zone is the rare fernbrake community. These fern dominated communities typically occur on the eastern side of the island on valley sides, steep slopes or sheltered valley floors. The dominant fern in most of these communities is Polystichum vestitum and grows up to 70cm in height. Occasionally it forms pure, dense stands in which few other plants are capable of growing. It more commonly grows in conjunction with Poa foliosa, Stilbocarpa polaris and Pleurophyllum hookeri.
Lusitania Bay landslide
| The coastal slopes are subject to two major forms of disturbance: landslips caused by seismic activity, or occasionally by heavy rainfall, and by grazing from rabbits. Macquarie Island is seismically active and subject to frequent earthquakes. These earthquakes cause regular landslips in this region, which may even denude areas down to the bedrock. Revegetation may then be a very slow successional process. Landslips may also occur during heavy rainfall, particularly following dry periods.
Coastal slopes support substantial populations of burrow nesting seabirds, and are favoured habitats of introduced black rats, mice and rabbits.
Because of the frequent landslips, heavy grazing pressures and burrowing animal activity, the vegetation is often in a state of flux. Both landslips and grazing can convert areas of tall tussock grassland to short grassland. Landslips may initiate the change, and grazing then maintains the vegetation as a short grassland. With the management of rabbit numbers from control programs, tall tussock grassland appears to be spreading.
Links
Australian Antarctic Science (AAS) projects relating to vegetation on Macquarie Island
Australian Antarctic publications relating to vegetation
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