Summary
This study represents the first investigation into the feasibility of using remote sensing to map and monitor the vegetation of sub-Antarctic islands. There have previously been no studies using satellite technology to remotely sense vegetation change in the Antarctic or sub-Antarctic regions, although it has been successfully used in Arctic vegetation studies. The sub-Antarctic Islands have been experiencing increasing temperatures as a result of global climate change for the last 50 years. This, together with anthropogenic disturbance from increased human activity on the islands, has caused considerable changes to many of the ecosystems of the sub-Antarctic and is expected to continue to do so at an accelerated rate. Due their inherent isolation and relatively undisturbed status, the sub-Antarctic islands provide an ideal natural model for monitoring and predicting the natural biological responses associated with climate change and hence there is great advantage in being able to map and monitor the vegetation change on the sub-Antarctic islands. Remote sensing provides an attractive alternative to current conventional methods of vegetation mapping on sub-Antarctic islands, which are time consuming, logistically difficult and costly, because it has the capability to map and monitor vegetation change whilst minimising human impacts to the islands and overcoming logistical difficulties. The feasibility of using remote sensing to map and monitor the vegetation on Heard Island (53„a05¡¦S, 73„a30¡¦E) was assessed using IKONOS, Hyperion and SPOT XS imagery of the eastern half of Heard Island acquired during summer 2003/04. The accuracy of the vegetation thematic maps produced from these images were assessed at three scales of classification, coarse (vegetated, non-vegetated), medium (vegetation density) and fine (individual vegetation communities). The accuracies produced by each of the sensors were compared, as was their data availability, continuity, and cost to determine the feasibility of their use for Heard Island vegetation mapping and monitoring. Remote sensing was found to be a feasible option for mapping the vegetation of Heard Island at the coarse scale, providing thematic map accuracies comparable to conventional mapping methods. This scale would provide highly accurate information on the extent, range and distribution of vegetation on Heard Island, as well as the colonisation of new areas and spread of vegetation over time SPOT XS was found to be the most cost-effective and feasible sensor for mapping the vegetation of Heard Island as it provides the best data availability and continuity of the three sensors assessed whilst providing similar thematic map accuracies. Remote sensing was not found to be a feasible option for mapping the vegetation of Heard Island at more detailed levels (such as community level), as the sensors cannot obtain this information with accuracies that could be used in an operational capacity