Response of juvenile Melaleuca halmaturorum to flooding: Management implications for a seasonal wetland, Bool Lagoon, South Australia

The response of M. halmaturorum was measured to determine the ability of juvenile plants to survive flooding and to examine how this influenced plant growth. Seedlings and one- and two-year-old plants were flooded to 0% (control), 50% or 100% of their initial height for periods of three to 14 weeks, followed by an eight-week recovery period. Only 22% of seedlings survived five weeks of 100% coverage, but these died during the recovery period. The older plants survived the flooding treatments well, but as duration increased so survival through the recovery period declined. After 100% coverage for six weeks followed by the recovery period, only 29% survived. Stem linear extension rates corresponding to these survival rates were used to predict the survival of juvenile M. halmaturorum in Bool Lagoon, South Australia. The results showed that, with the current water regime, natural recruitment would occur only at the highest elevation but that this could be improved by planting older, taller plants at lower elevations. Indices of growth showed that flooded plants performed poorly compared with the controls as duration and percentage of coverage increased. The data suggested that coverage inhibited plant growth during the flood period, but there was a further, interactive response to duration that became apparent after the post-flood recovery period. An interpretation of these results is that M. halmaturorum in its juvenile stages is intermediate between a flood-sensitive and a flood-tolerant species because it is able to recover from short floods of three weeks or less but performs poorly if floods exceed six to nine weeks.Matthew Denton and George G. Gan