Summary of the final report on the Australian Flora Foundation funded project:

Measuring and managing the impact of secondary salinisation on riparian flora
Alan Lymbery, Michelle Ingram and Farhan Bokhari
Fish Health Unit, School of Veterinary and Biomedical Sciences, Murdoch University   Grant details   Final report

Summary
The secondary salinisation of streams and rivers, largely as a consequence of land clearing, is a major environmental problem in Australia. Although the detrimental effects of salinity on aquatic organisms has been well documented, there is little information on how salinisation affects riparian flora and fauna. Such information is necessary, first to accurately assess species at most risk from salinisation, and second, to identify suitable candidate species for the rehabilitation of riparian zones which have already been affected by salinisation.

We examined the impacts of salinisation on riparian plants and their associated invertebrate fauna in two adjacent catchments, one of which had been partially cleared and the other left uncleared, of the Collie River in the south west of Western Australia. By comparing riparian plant and invertebrate communities between the catchments and also along a salinity gradient within the partially cleared catchment, we were able determine that increasing soil salinity was associated with a reduction in the diversity of riparian plant species and of plant-dwelling invertebrate species.

The reduction in plant species diversity occurred because of the detrimental effects of salinity on particular plant species. In controlled laboratory trials, we showed that increasing salinity decreased the germination rates of Bossiaea eriocarpa, Hypocalymma angustifolium, Hakea lissocarpha, Hakea undulata and Hakea varia, all of which were relatively more common in low soil salinities in the catchments, while there was no effect of salinity on the germination rates of Melaleuca viminea, Xanthorrhoea preissii and Corymbia calophylla, which were all relatively more common at high soil salinities.

The reduction in invertebrate species diversity was largely due to fewer species of spiders being found at high soil salinities. We suggest that this occurs because increasing soil salinity leads to a decrease in plant species diversity, which in turn reduces the structural complexity of the habitat for spiders, particularly those species which capture their prey by building webs. This indicates that the effect of salinisation on riparian plants may have consequences which impact on many aspects of the functioning of riparian ecosystems.