Extending over an area of 62,000 hectares Dirk Hartog Island National Park is the largest island off the Western Australian coast. The management of weed species has previously been identified as a priority for the island. This includes management of high risk species and preventing the further introduction of weed species to the island. The purpose of the Weed Management and Action Plan is to provide the Department of Parks and Wildlife with an integrated suite of methods to effectively manage existing and potential weed threats.
Astron undertook a Baseline Weed Survey of Dirk Hartog Island to record the distribution, abundance and cover of existing weed species. A total of 49 weed species were identified, ranked and the species rankings were then used to identify 15 weed species as a priority for management. An Integrated Weed Management methodology was used to develop the Management and Action Plan. A framework has been developed to allow adaptive responses to be undertaken in order to achieve management objectives. Weed Surveillance Areas are surveyed to detect new weed introductions, control and eradication is undertaken within Weed Management Areas and Weed Monitoring Sites are surveyed to record trends in weed levels.
The island was divided using a grid system where abundance of each weed species was estimated in each cell. Transects made up of ten 25 × 25 m quadrats were systematically placed every 2 km along the road. Additional transects were placed near sites with potential disturbance. Within each quadrat, a weed record point was placed over an area with the highest density for each weed species. Generally speaking, more weeds were found within 500 m of historical infrastructure compared with greater than 500 m from historical infrastructure. Consequently, the mean number of weed record points was estimated separately for areas within 500 m of historical infrastructure and areas greater than 500 m from historical infrastructure.