Relative Drought Resistance of Tristaniopsis laurina and Acmena smithii From Riparian Warm Temperate Rainforest in Victoria

The drought tolerances of the warm temperate rainforest species Tristaniopsis laurina and Acmena smithii were examined. Using pressure bomb techniques the tissue water relations of hardened juvenile and adult material were measured. T. laurina showed relatively little physiological drought tolerance in either the juvenile or adult plants, whereas A. smithii showed an increase in physiological drought tolerance in adult plants. Direct observations of droughted hardened 9-month-old seedlings revealed a relatively high leaf conductance in T. laurina seedlings with wilting becoming generalised after 9 days of droughting. All T. laurina plants rehydrated after 15 days of drought survived albeit with significant leaf abscission, but only 2 of the 5 plants rehydrated after 20 days of drought recovered and these were defoliated. Stomatal resistances were higher in droughted A. smithii seedlings and wilting did not become generalised until after 14 days of droughting. All A. smithii plants recovered when rehydrated after 20 days of droughting with little or no sign of leaf abscission. Leaves of T. laurina and A. smithii became scorched when subjected to temperatures of 50°C and 60°C respectively. The extent to which these differences delimit the distribution of these species in the relatively dry warm temperate rainforest communities of Gippsland in Victoria is discussed.