GROUNDWATER RESPONSE TO REFORESTATION IN THE DARLING RANGE OF WESTERN-AUSTRALIA

Replacement of deep-rooted perennial vegetation with annual crops and pastures has led to rising groundwater tables and transport of previously stored salts to streams in southwest Western Australia. Trials to determine the potential of various reforestation strategies to reverse this process by lowering the groundwater table were commenced in 1976-1981. Results are reported from six experimental sites for the period 1979-1986. Despite the mean annual rainfall of the experimental period being 10% below the 1926-1986 mean, groundwater levels under pasture rose by up to 1.2m. The change in groundwater levels beneath reforestation ranged from a 0.6-m increase to a 3-m decrease relative to the ground surface. Groundwater levels under reforestation in all cases decreased relative to groundwater levels under pasture. The magnitude of this reduction was shown to increase with the proportion of cleared area reforested and with the crown cover of the reforestation. The salinity of the water table decreased by 12% under reforestation and by 32% under pasture over the period 1979-1986. © 1990.