Monitoring vegetation recovery in the early stages of the Dirk Hartog Island Restoration Programme using high temporal frequency Landsat imagery

Abstract

Dirk Hartog Island is the largest island off the West Australian coast. From the 1860s to 2008, the island was managed as a pastoral lease. In 2009, the island was gazetted as a National Park and the process of removing introduced animals, to allow for the reintroduction of a suite of 12 native mammal species, began. With the removal of high numbers of goats and sheep concerns were raised regarding the proliferation of weed species (which would no longer be controlled through grazing) and the ability of the island’s native vegetation to recover. A vegetation monitoring programme was developed which integrated detailed floristic surveys, repeated site photography and Landsat time series data to provide a comprehensive picture of how the island’s vegetation cover had changed since destocking. The integration of these elements has allowed present-day observations to be put into context of longer term landscape dynamics. Through statistical analysis of temporal sequences of Landsat satellite imagery, the timing of changes to phenology and cover at monitoring sites was related directly to the management action of stock removal. With the use of field observations, the species responsible for the increase in cover were identified. These data sources, when analysed together, allowed management to have confidence that, following destocking, native vegetation cover is increasing.