Recovery of vegetation cover following logging and regeneration in the southern forest of Western Australia and the short term hydrologic implications

Abstract

A survey was conducted in 1986 in a series of stands of different ages in the lower rainfall jarrah (Eucalyptus marginata) forest (< 1100 mm mean annual rainfall), high rainfall jarrah forest (> 1100 mm) and karri (E. diversicolor) forest (> 1000 mm), in the southern forest of Western Australia, in order to assess the recovery of vegetation cover as a function of time since regeneration. The data were then used to estimate the time required for the water balance of regenerating stands to return to the pre-logging state. Overstorey cover and total cover were assessed. In both types of jarrah forest, both overstorey cover and total cover exceeded 80 per cent of the value for unlogged stands within five years of regeneration, and had exceeded 90 per cent within 10 years. They were very close to the value of unlogged stands in about 20 years, and thereafter remained at that value. In karri forest, total cover reached the value for unlogged stands five years after the beginning of regeneration, rose for five more years, and then stabilised at a value slightly above the value for unlogged stands. Overstorey cover reached the value for unlogged stands within 10 years, continued to increase for another 10 years, and then stabilised above the value for the unlogged stands. Changes in groundwater levels were related to total cover of regenerating karri stands. Changes in groundwater levels were also indicative of changes in water use and other components of the water balance. Rises in groundwater level in regenerating karri stands ceased when total cover was close to the value for unlogged stands. Thus, the quick recovery of vegetation cover indicated that the water balance of logged jarrah and karri stands in south-west Western Australia was similar to that of unlogged stands after about 10 years of regeneration.