The transpiration response by four topographically distributed Eucalyptus species, to rainfall occurring during drought in south eastern Australia

Vegetation covers a substantial proportion of the terrestrial Earth surface and where removed from human influence has evolved influenced mainly by climatic and edaphic constraints. Over the past 200 years, substantial tracts of the wheat-sheep belt of southern Australia has been cleared of native vegetation and replaced by annual crop and pasture species. As a consequence, there has been a change in the water balance of many catchments as now more water leaks beneath the roots of introduced plants, contributing to groundwater rise and expansion in the amount of land affected by salinization. In an attempt to arrest root zone leakage, scientists and managers acknowledge the need for new agricultural practices which mimic the ecohydrological behaviour patterns of remnant vegetation. In this paper, we examine the water use characteristics of four woodland Eucalyptus species growing in different topographic and edaphic environments in south eastern Australia. Eucalyptus sideroxylon and E. rossii were the sub- and dominant species inhabiting the stony ridges, while in the adjacent valleys E macrorhyncha and E. albens were the sub- and dominant species, respectively. At the two locations, sub-dominant species were highly responsive to episodic rainfall events both during and following drought, and exhibited distinct seasonality in daily transpiration rate; while the dominant species at each location was less responsive to rainfall and water use appeared to be less seasonally dependent. Analysis of the water use response indicated that the two sub-dominant species had shallower roots while the major of roots of the dominant trees were likely to be located deeper in the substratum. This suggested that the stony ridges may store water deeper in the substratum than previously thought, to sustain some remnant vegetation over the dry summers, and ultimately, contribute less recharge to groundwater.