Flora and vegetation communities of selected islands off the Kimberley coast of Western Australia

WA Museum Records and Supplements | Updated 7 years ago

ABSTRACT – A systematic survey of flora and floristic communities was undertaken on 24 selected inshore islands off the Northern Kimberley (NK) coast between 2007 and 2010. One hundred and thirty seven 50 x 50 m quadrats were sampled for floristics and surface soils, and site attributes recorded. Quadrat sampling was supplemented by general collecting to further document the floristics of major substrates and habitats of each island. We recorded 1005 taxa from the surveyed islands, of which, 403 taxa were new records for the collective islands of the NK bioregion. Based on existing Western Australian Herbarium collections and current survey records, the flora recorded from the islands represents approximately 49 percent of the NK bioregion flora. A total of 57 taxa of conservation significance were recorded from the surveyed islands. Few taxa appear to be restricted to islands. Very few weed species were recorded, except from the islands with a modern history of settlement. Ten floristic groups were defi ned by the classifi cation of species presence/absence within quadrats. Broad geology coupled with climate and local edaphic parameters appeared to be the main factors influencing the vegetation patterns observed on the islands sampled. Among quadrats on the hard/ rocky substrates, there was a compositional gradation from the plant communities of the sandstone geologies to the more fertile volcanic/dolerite substrates, which was reflected in the values of the soil parameters. In terms of the conservation signifi cance of the islands as a whole, the largest and wettest islands were shown to be particularly important as they supported the highest number of NK bioregion endemic plant species. Highest numbers of priority taxa also tended to occur on the largest islands. However, some of the drier islands had unique species assemblages with elements of arid/semi-arid zone flora that were not well represented on other islands. Future management of the islands requires strategies that minimize both the risk of exotic weed introductions, and inappropriate fire that would threaten the persistence of fi re-sensitive vegetation.