Manipulating catchment water balance using plantation and farm forestry: Case studies from south-western Australia
Harper, R.J., Mauger, G., Robinson, N., McGrath, J.F., Smettem, K.R.J., Bartle, J.R. and George, R.J. (2000) Manipulating catchment water balance using plantation and farm forestry: Case studies from south-western Australia. In: Plantations, Farm Forestry and Water Proceedings of a national workshop, 20 - 21 July, Melbourne, Australia pp. 44-50.
Three case studies are presented that describe the use of plantations and farm forestry in south-western Australia to tackle the problems of maintaining water supply and overcoming dryland salinity. The approaches we describe have both geographic and temporal components. The case studies are (1) the revegetation of partially cleared catchments with rainfall >600 mm yr-1 to protect surface water supplies from salinisation; (2) the recent widespread establishment of Eucalyptus globulus (Tasmanian blue gum) plantations on mostly cleared farmland with rainfall >600 mm yr-1; and (3) the extension of farm forestry into lower (300-600 mm yr-1) rainfall areas.
Dryland salinity results from an increase in infiltration and drainage to groundwater systems following replacement of natural vegetation with shallow-rooted annual agricultural plants. Revegetation can restore the hydrological balance, but given the current scale of and increase in salinity in this area, with 6 M ha eventually likely to be affected, this will have to be extensive. Several issues need to be confronted before such revegetation. These include (a) social and economic considerations; (b) integrating the trees with agriculture; (c) resolving technical issues associated with establishing trees on farmland; and (d) the development of economically viable tree crop industries to promote adoption.
Some of these issues have been resolved for Tasmanian blue gums, but in many cases these have been established as broad-scale plantations and the problems associated with integration have been avoided. Potential constraints on the long-term sustainability of the Tasmanian blue gum industry include (a) a reduction in yield with declining rainfall; (b) the ever-present risk of drought in a Mediterranean climate; and (c) the depletion of stored soil water in the first rotation with likely consequences on second-rotation yields. In low-rainfall areas commercial farm forestry options do not yet exist but are required at a scale of 2-3 M ha. Here the challenges are to develop tree-based industries that deliver both profits and environmental benefits.
|Publication Type:||Conference Paper|
|Copyright:||© 2001 Rural Industries Research and Development Corporation.|
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