Leaf water potentials, fire and the regeneration of mallee eucalypts in semi-arid, south-eastern Australia

Abstract

Comparisons of predawn leaf water potential were made between adults, seedlings and coppicing lignotubers of yellow mallee, Eucalyptus incrassata Labill., during a period of severe drought between December 1981 and March 1983. Measurements were made on plants from areas which were one year, four years, and more than twenty years unburnt.Seedlings and coppice regrowth from sites burnt one year previously had significantly higher leaf water potentials than plants from older sites. Little change in water status of long-established plants occurred, despite the drought. There was no difference in the water potentials of plants from sites which were more than four years unburnt. Seedlings of both the one year old and four year old cohorts suffered mortality rates of more than 50% during the summer season towards the end of the drought when leaf water potentials had decreased to -4 MPa.It is suggested that the difference in plant water status, observed between sites which were one year unburnt and older sites, was due to a temporary cessation of the depletion of soil moisture reserves by the vegetation. Fire results in complete defoliation of established vegetation and it is some years before community evapotranspiration returns to pre-fire levels.