LOWERING OF A SHALLOW, SALINE WATER-TABLE BY EXTENSIVE EUCALYPT REFORESTATION

Land and stream salinisation in Western Australia has occurred as a result of the clearing of native vegetation for agricultural development. One approach to controlling the salinisation, extensive reforestation, has been tested on a site which was 35% cleared and converted to pasture in the 1950s. By 1979 saline ground water was discharging in the valley where the clearing had taken place. At that time 63 Eucalyptus and two Pinus species were planted in 0.5 ha blocks across the site, covering some 70% of the cleared land. The reforestation has been successful in substantially lowering the saline groundwater table across the site. Over the 1980-1989 period, the average minimum groundwater levels beneath reforestation declined by 5.5 m relative to the ground level and by 7.3 m relative to a nearby pasture control site. After the first 3 years the rate of decline was near-uniform with time. The average salinity of the ground water beneath reforestation decreased by 11%.