Prof. Eamus said that globally, drought is increasing in frequency and severity, putting further pressure on groundwater resources and hence even threatening forests growing in wet regions.

He said this is the first study to have tracked how groundwater depth affects trees across multiple scales, including small-scale (cellular, leaf), medium-scale (branches and whole tree) and larger scales (entire stands of trees). "We found that the whole system is tightly linked -- one change can affect everything else.

"Based on this study, we can also develop a mathematical model to help find out how much groundwater we can extract from woodlands growing in wet environments. This can potentially be adapted for use in forests worldwide."

The research indicates that despite their abundant rainfall, we should still be concerned about how groundwater extraction affects the humid areas of the world, Prof. Eamus added. "We're already facing a global water crisis -- and we can't simply continue to extract groundwater from underneath forests without potentially damaging the forest.

"Not only that, since a lot of groundwater flows into rivers, we can also expect to see changes in river flow when groundwater extraction is excessive.

"Studies like these allow us to better understand how ecosystems use groundwater and how sensitive they are to changes in groundwater depth. For instance, we now know the limit of groundwater extraction from this forest in New South Wales, so we won't risk pumping out too much and killing the trees in times of drought."

The National Centre for Groundwater Research and Training is an Australian Government initiative, supported by the Australian Research Council and the National Water Commission.