Planting trees on uplands (hills) is not enough to solve Australia's salinity problem, a Monash University study has found.

The study, by Dr Ian Cartwright from Monash's School of Geosciences and colleagues, has quantified for the first time the amount of water that seeps into the groundwater in northern Victoria, causing water levels to rise and producing dryland salinity.

Dryland salinity is Australia's most serious environmental problem - after global warming - and has a major affect on the productivity of agricultural land and rural infrastructure. It has long been known that dryland salinity results from the clearing of native vegetation, which is an efficient absorber of rainfall.

"This clearing results in more rainfall entering the groundwater -- a process called recharge -- which in turn causes the water table to rise," Dr Cartwright said.

"What we set out to understand was where the increases in recharge occurred and how much extra water was being added to the groundwater."

The team showed that increased recharge occurs across the landscape - on the hills and also on the lower lying areas. This is in contrast to some models of dryland salinity that assume most recharge is on the uplands.

The results have been published in the Journal of Hydrology.

Dr Cartwright said the landscape-wide recharge demonstrated the need for the whole landscape to be managed if dryland salinity was to be resolved.

"These findings have significant implications for the way Australia tackles dryland salinity," he said. "Mitigation methods such as planting trees only on the uplands will not entirely solve the problem.

"The situation needs consistent monitoring. In some areas the salinity problem may be appearing to ease, but that is in part due to the drought lowering the water table. If and when rainfall increases, recharge will increase and that will cause the water table to rise -- this is especially the case as recharge occurs across the landscape and water tables will quickly respond to the additional rainfall."