The marked flooding tolerance of seedlings of a threatened swamp gum: implications for the restoration of critical wetland forests

Abstract

Wetland forests home to the last remaining wild populations of the helmeted honeyeater and lowland Leadbeater’s possum are under threat from tree dieback and a lack of natural regeneration, putatively the result of an altered hydrological regime. To restore these critical wetland forests, a better understanding of the flooding tolerance of the seedlings of the dominant tree species, Eucalyptus camphora subsp. humeana L.A.S.Johnson & K.D.Hill, is essential. I tested the effect of flooding on the establishment and growth of E. camphora seedlings in three nursery-based experiments. These experiments involved E. camphora seedlings of different ages (1, 3, and 8 months old) being subjected to different depths and durations (up to 12 months) of flooding. Eucalyptus camphora seedlings were able to survive and grow while flooded for 12 months as long as they were emergent. However, flooding negatively affected the growth of E. camphora seedlings, with these effects increasing with increasing depth and duration of flooding, and decreasing seedling age. The ability of E. camphora seedlings to survive prolonged shallow flooding is considerable, an ability enabled by its rapid and extensive production of aerenchyma tissue and stem-borne adventitious roots under flooded conditions. Nonetheless, conditions for E. camphora seedling establishment and growth are likely to improve with reduced flooding, with an absence of flooding during its growth period (early spring–late summer) most favourable.