Growth of species in a tree plantation and its influence on salinity and groundwater in the 400 mm rainfall region of south-western Australia

A multi-specied Eucalyptus tree plantation was established in 1976 on about 12% of a first-order farm catchment above a saline seep. The main objective was to rank species for water use (as assessed by leaf area and survival) to assist future reclamation of saline seeps in the region. The catchment had a permanent deep aquifer confined in its lower third and a shallow seasonal aquifer. Changes in elevation and salinity of groundwater were monitored by piezometers. Larger stores of salt were found in the soil profile downslope than at midslope. There was visual evidence of extensive discharge of salt in the seep during the whole period of the experiment. Chloride in the deep aquifer fell by approximately 20% between 1977 and 1984, the decline being greater at midslope than downslope. Tree growth was rapid until 1981 but declined thereafter. Water-level changes and perched water presence indicated greater water use by the plantation than by adjacent crop and pasture. After 15 years, the most promising species were Eucalyptus cladocalyx var. nana, E. cladocalyx, E. occidentalis, and E. sargentii. A significant factor in the failure of the plantation to control the seepage was the location of the plantation in a zone where the aquifer is apparently confined.