Land use which reduces tree canopy density and the impact of Phytophthora cinnamomi are believed
to be altering the hydrological balance of parts of the northern jarrah forest, Western Australia. In
the drier eastern zones of the forest, replacement plant communities must maintain the soil-salt-water
balance to prevent significant increases in salinization of streams in water supply catchments. Daily
and seasonal patterns of the diffusive resistance of leaves and xylem pressure potential were determined
for the major natural dominant of the region, Eucalyptus marginata, and five other species of
Eucalyptus used in rehabilitation.
Three types of daily and seasonal patterns were observed. E. marginata and E. calophylla exhibited
little stomatal control of water loss, and leaf resistances remained low throughout the study period
(type 1). E. maculata, E. resinifera and E. saligna exhibited marked stomatal regulation during summer
days when xylem pressure potentials fell below -2.O MPa (type 2). E. wandoo (type 3) also controlled
water loss but developed xylem pressure potentials far lower than all other species tested (<-3.0 MPa).
Although none of the species tested replicated the summer stomatal resistance and xylem pressure
potential patterns of E. marginata, it is suggested that total annual water use should be examined
before selecting the most appropriate species to rehabilitate disturbed sites in the eastern zones of
the northern jarrah forest region.
