The status and distribution of naturalised alien plants on the islands of the west coast of Western Australia.
Alien plants pose a substantial threat to island ecosystems in Australia and worldwide. A better understanding of weed distributions is necessary to more effectively manage natural resources on islands. To address this for Western Australian islands, we assembled a database of all available records of alien plants on these islands. In the second paper in this series, we report on the distribution of records from all islands located along the west coast of Western Australia. We defined the west coast as the coastline within the boundaries of the South West, Swan and Midwest regions of the Department of Parks and Wildlife. This area of coastline stretches from Black Point (near Cape Leeuwin) in the south, to Waroora Station (near Coral Bay) in the north. From 4049 individual records, a total of 317 alien plant species were recorded on the 206 islands with existing weed records. A disproportionately large number of weed species were recorded on islands near Perth, estuarine islands, and islands with a history of intensive human activity. Some of the species recorded as present on the islands are known to be serious environmental weeds, including mother of millions (Bryophyllum delagoense), sea spurge (Euphorbia paralias), cleavers (Galium aparine), African boxthorn (Lycium ferocissimum), tree mallow (Malva arborea), ice plant (Mesembryanthemum crystallinum), common prickly pear (Opuntia stricta), sea spinach (Tetragonia decumbens), and golden crownbeard (Verbesina encelioides). The development of management plans to address these species and the survey of islands adjacent to known infestations should be conservation priorities for the west coast islands. Improved biosecurity procedures and enforcement could prevent the establishment of new weed populations on islands and reduce the future costs associated with the management of infestations.