In the northern Murray–Darling Basin (MDB), Australia, the displacement of native floodplain grasses by Phyla canescens (Lippia), an exotic herb, coincided with a reduced frequency of floodplain inundation owing to river regulation. Although river regulation and P. canescens occur in the southern MDB, P. canescens abundance has not increased significantly since 1988. This work reports on the current distribution of P. canescens and the native grass Sporobolus mitchellii on the lower River Murray. It demonstrates that there are significant differences in the edaphic characteristics of sites occupied by the two species and co-occurrence is rare. To explain this observation, two factors were investigated: the resilience of S. mitchellii to invasion by P. canescens and the response of both species to artificial spring floods. At initial densities of >25%, S. mitchellii exhibited strong resilience to invasion by P. canescens. The growth response of both species to spring floods was similar. However, P. canescens reproduced asexually when inundated and, on exposure, exhibited a root distribution that would enhance its capacity to survive future droughts. In contrast, S. mitchellii was more tolerant of low soil moisture than P. canescens. The re-introduction of spring floods could favour the expansion of P. canescens.
Linking inundation timing and extent to ecological response models using the Murray-Darling Basin Floodplain Inundation Model (MDB-FIM)
