Sustaining recovery in red gum, black box and lignum in the Murray River Valley: clues from natural phenological cycles to guide environmental watering

ABSTRACT The natural flow regime of the Murray River in south-eastern Australia has been fundamentally altered through regulation and extraction, with fewer, shorter floods, changing seasonality of flows and reduced floodplain connectivity. Ecosystems which evolved over millenia show serious stress and decline under the regulated regime. Environmental water allocations being returned to Murray Valley ecosystems to halt the decline and improve river health are not sufficient to re-create missing floods, but aim to mimic key elements of the natural water regime. For floodplain vegetation communities, the missing element is seasonal water availability to maintain condition of mature trees and trigger germination of seedlings. Dominant perennial vegetation species river red gum (Eucalyptus camaldulensis), black box (E. largiflorens) and lignum (Muehlenbeckia florulenta) suffered significant stress and death during the severe Millenium drought (2000–2010), but drought-breaking floods in 2010–2012 replenished soil moisture reserves. A new generation of seedlings germinated, and many environmental watering projects now focus on enhancing survival of these seedlings. Previous studies suggested that timing of phenological stages can indicate key timing for beneficial delivery of environmental water. These findings are being tested at Lower Murray Valley sites, to identify optimum timing for watering to support recovery in floodplain vegetation communities.