In our quest to prepare Australian soils for agriculture, we cleared trees by the billion. Yet trees played a crucial role in maintaining the water balance in our ancient soil profiles. It was our success in clearing trees that has led to the development of dryland salinity. This is because trees develop extensive root systems to trap the water, which is then used for tree growth or returned to the atmosphere by evaporation and transpiration. Scientists estimate that the amount of water that percolates below the root zone of crops and pastures can be 10 to 100 times the amount percolating below trees.
Trees also play a role in discharging ground water.
The roots of many Australian tree species reach down deep into the ground, often making contact with the water table. During drought, such trees use this water in order to survive and keep growing. In contrast, annual crops that farmers plant on cleared land usually don't have deep roots. Moreover, many crops only grow during winter, spring and early summer while most Australian trees require water all year round. If salinisation is caused by the removal of trees from the landscape, it seems logical that putting them back will solve the problem.