MWRPP Report 20.10: Multiple vegetation benefits of Macclesfield Creek floodplain engagement works.

On 19/9/2018 two temporary weirs were installed, one at each of two locations along a channelised section of the Macclesfield Creek within the Yellingbo Nature Conservation Reserve ( Figure 1). Their purpose was to reengage disconnected floodplain areas and improve vegetation condition in areas supporting lowland Leadbeater’s Possums (Permit no. MWA-106320). The scale of the weirs was considered small, the structures temporary, low risk, and easily constructed using sandbags (Jacobs 2018). A three-year monitoring program was established by The University of Melbourne to monitor for potential floodplain watering and vegetation benefits. Both weirs have been successful in diverting large volumes of water from the channel and flooding large extents of the Maccclesfield Creek floodplain downstream and adjacent to each of the weirs. In these locations and at two corresponding control and reference sites (six sites in total) we monitored the: success of direct seeding of Eucalyptus camphora; growth of planted E. camphora, Leptospermum lanigerum and Melaleuca squarrosa seedlings; growth of E. camphora trees; and E. camphora seedfall. Flooding had multiple benefits, including increased germination from direct seeding, increased growth of planted seedlings and extant trees; and the triggering of seedfall. The details of these benefits are the focus of a couple of scientific journal papers in preparation, and a summary (and not the full details) of these results are presented here. Given the likelihood of continued and more extensive benefits of further floodplain engagement, we recommend the following: i) That the existing weirs be modified as necessary to ensure their structural integrity and longevity; ii) Additional weirs be strategically introduced into the channelised section of the Macclesfield Creek to promote further floodplain engagement; iii) Reinstating appropriate water regimes should be complemented by revegetation and consider species-specific hydrological requirements to facilitate riparian forest regeneration; iv) Planting should ideally be undertaken at the end of the flooding season so that flood exposure (duration) is within species’ tolerance ranges and so that seedlings can take advantage of recharged soil moistures. Where possible, the more flood tolerant Leptospermum lanigerum and Melaleuca squarrosa should be planted earlier and closer to the channel (or within depressions) than the less flood tolerant E. camphora.