While water users make competing claims for groundwater, researchers say that there is an urgent need for more information about the cumulative effect of thousands of hectares of plantations planned for the region.

Groundwater is the source of domestic water supplies for Mount Gambier and surrounding regions and is vital to irrigated agriculture in the area.

CSIRO recently completed a report for the SA Department for Water Resources to review existing knowledge on plantation forest water requirements in relation to groundwater resources in the south-east of South Australia.

"Plantations are efficient users of water and prevent nearly all water from reaching groundwater," says Dr Peter Dillon, CSIRO Land and Water, one of the authors of the report.

"Rain falling on shallow-rooted annual crops and pastures, here as in other parts of Australia, is much more likely to 'leak' past the root zone and enter the groundwater", he says.

"Besides reducing water leakage to the groundwater, plantations can also under some circumstances use groundwater.

"This happens where the water table is close to the surface, typically less than 5 metres, and is accessible by the tree roots.

"If we over-use water for irrigation, plantations or domestic water use, the availability of water for other uses - including wetlands - would be affected."

Most of the new plantations in the region are currently being established over shallow water tables.

Based on the limited data available, the report forecasts that the new eucalypt plantations will use more groundwater than do existing plantations. This is because most of the existing plantations in the region overlie a relatively deep water table so their net use of groundwater is small.

The report notes that there is still a level of uncertainty about how much groundwater the new plantations will take up.

The forest industry is working with the Department for Water Resources and CSIRO to better define the water use of plantations. Dr Richard Benyon of CSIRO Forestry and Forest Products is at the beginning of a three year collaborative project to investigate the water use of plantations under a wider range of conditions than have been studied so far.

CSIRO's findings can help the forest industry target locations for new plantations on sites where the impact on water resources will be least. There are also several management options which may reduce plantation water use including reducing the proportion of land planted, thinning, shorter harvesting cycles and fallow periods between tree rotations. At any given time, tree coverage in a plantation area can vary from zero to full cover depending on the stage of plantation growth.

"The forest industry has a long term view of sustainability and the maintenance of the water resource is as essential to forests as it is for irrigation, water supply and wetlands," says Dr Dillon.

"Managing the groundwater balance, by managing the competing demands on this essential resource needs informed decision making based on sound research and continued monitoring," he says. - By Nick Goldie

[Contact: Dr. Peter Dillon, Nick Goldie ]

14-Aug-2001