Patterns of plant invasion in disturbed dryland riverine ecosystems

Plant invasions can be facilitated by natural or anthropogenic disturbance. Non-native plant invasion is therefore expected to be especially high where land that is used for agriculture intersects with disturbance-prone riparian ecosystems. We investigated patterns and drivers of plant invasion in the semi-arid agricultural region of the northern Murray-Darling Basin in eastern Australia. We surveyed the floodplain and riparian vegetation at 22 sites, recording all strata and cover of plant taxa, which we categorised by biogeographic origin (native/non-native) and growth form. We found that native species were dominant in the standing vegetation of the surveyed sites and were represented by a breadth of growth forms across all structural canopy layers. Non-native grasses, forbs and shrubs were also prominent, comprising at least 30% of all recorded species. On occasion, the majority of vegetative cover (up to 90%) in surveyed sites was made up of non-native grasses or forbs. Non-native trees were rare, with just one taxon ( Salix sp.) recorded at a single site, indicating that dispersal and other ecological constraints have restricted establishment. Native and non-native species composition did not vary significantly between habitat types (riparian versus floodplain), suggesting that the species pool of this region is largely comprised of habitat generalists. Dryland riparian ecosystems are complex, dynamic and variable, subject to an array of natural and anthropogenic pressures. Plant invasion appeared to be shaped by an interplay of factors, including catchment geography, site-based variability, land use and hydrology, with the importance of environmental drivers varying among habitat type and between native and non-native assemblages. Environmental management that addresses the drivers of native species decline and non-native invasion will be important for preserving dominance of native vegetation in floodplain and riparian ecosystems of the northern Murray-Darling Basin.