MWRPP Report 19.2: ockatoo Swamp Monitoring Program 2015–2019: Early vegetation response to hydrology works.

Five years of data have now been collected for the Cockatoo Swamp monitoring program that was established to assess hydrological and vegetation responses to hydrology works aimed at restoring critical Helmeted Honeyeater and Leadbeater’s Possum habitat at the Yellingbo Nature Conservation Reserve. As part of the works program, levee removal works were undertaken in late 2017, and a pumping trial is being conducted for which the first full season of pumping was completed in summer–autumn 2019. Due to the relatively dry conditions since the introduction of levee breaks, widespread reconnection of floodplain areas behind the levee via the breaks has not yet occurred. Apart from the absence of moderate or large floods, the incised nature of the channel i n the vicinity of levee breaks limits overbank flooding and thus the engagement of the levee breaks. However, at the two most downstream levee breaks, some good engagement has been achieved and regeneration of some native wetland vegetation at these sites has been observed. The effectiveness of the pumping trial is not yet able to be determined, with the first full year of pumping only just completed. Moreover, early 2019 was particularly dry thus the ability of the pumps to run was hampered (and ironically there was reduced need the for them to do so). Nonetheless, vegetation condition monitoring to date supports the contention that the pumping trial, via reduced water levels during the growing season, has the potential to improve the condition of dieback-affected vegetation within the Cockatoo Swamp. Against the backdrop of a drying trend, there have been noteworthy changes in vegetation condition between 2015 and 2019. Most notably, there has been an increase in tree crown extent and stand condition (driven largely by increased shrub cover) at dieback-affected sites, and increased reproductive output (abundance of buds, flowers and cones) and seedfall of E. camphora. These observations provide evidence for the potential of dieback-affected areas to benefit from the pumping trial over the next three years via reduced duration and extent of flooding. Disconcertingly, there has been a large increase in the extent of the invasive Phalaris arundinacea in recent years, particularly at dieback-affected sites. This species is extremely invasive and difficult to control, and often forms monocultures preventing woody plant regeneration. It is advised that interventions to remove Phalaris and planting/direct seeding be trialled concurrently during periods of lowered water levels achieved via the pumping trials to develop successful approaches to restoring such areas.