Friday, March 11, 2016
Heard Island and McDonald Islands are uninhabited, barren, sub-Antarctic islands in the Southern Ocean, far due south of India and roughly 200 miles southeast of Kerguelen of the French Southern and Antarctic Lands. The islands are administered by Australia.The islands have an Antarctic climate, tempered by their maritime setting. The weather is marked by low seasonal and daily temperature ranges, persistent and generally low cloud cover, frequent precipitation and strong winds In this cold climate plant life is mainly limited to grasses, mosses and lichens. Low plant diversity reflects the islands’ isolation, small size, severe climate, the short, cool growing season and, for Heard Island, substantial permanent ice cover. The main environmental determinants of vegetation on subantarctic islands are wind exposure, water availability, parent soil composition, salt spray exposure, nutrient availability, disturbance by trampling (from seabirds and seals) and, possibly, altitude. At Heard Island, exposure to salt spray and the presence of breeding and moulting seabirds and seals are particularly strong influences on vegetation composition and structure in coastal areas.
The main indigenous animals are insects along with large populations of ocean-going seabirds, seals and penguins.Some plant species are spreading and modifying the structure and composition of communities, some of which are also increasing in distribution. It is likely that further changes will occur, and possibly at an accelerated rate. Changes in population numbers of seal and seabird species are also expected to affect the vegetation by changing nutrient availability and disturbance through trampling.