Linking science and management of invasive native macrophytes: 'Typha' within the River Murray, South Australia

Abstract

Community structure and ecological functioning of aquatic ecosystems throughout the world have been impacted by river regulation and intensive land use practices. These modified landscapes provide conditions conducive to the expansion of opportunistic invasive plant species. Although taxa native to south-eastern Australia, 'Typha domingensis' and 'T. orientalis' provide examples of invasive plants becoming an increasing threat to the ecological character of wetlands and creeks of the River Murray, South Australia. Management of these invasives requires frameworks such as adaptive comanagement (ACM) that combine the collaboration of community, stakeholders and scientists with the principle of adaptive management, which is particularly important addressing the management of invasive plants by citizen scientists (wetland managers). This research investigates wetland managers' perceptions of 'Typha'. It also questions whether there is a perceived impact of 'Typha' control on wetland biodiversity as well as their understanding of control methods as part of current wetland management practices. A temporal comparison of remote sensing images revealed that 'Typha' has increased its cover in the Riverland region and is physically blocking waterways and reducing flows, suggesting current control through wetting and drying wetlands and excavation is ineffective. Alternative methods for 'Typha' control were trialled in a field experiment to compare effectiveness and impact on aquatic diversity in both wetland and creek environments. Dredging is the most common control measure in this region and although effective at reducing short-term biomass, causes significant physical damage to habitats. Cutting 'Typha' below water level was also successful in reducing 'Typha' biomass, but the effectiveness of this control measure varied between the wetland and creek site. It is hypothesized that environmental factors intrinsic to each system such as water depth and sediment anoxia potentially limit the effectiveness of control techniques. An important lesson from this research was that some wetland managers' had poor knowledge of Typha and ecosystem responses, information that was key to developing frameworks for effective decisions on Typha control. This emphasises the importance of information exchange among scientists, managers, and communities and learning opportunities through the ACM process to effectively manage invasive native plants in freshwater ecosystems.