Vegetation can reduce groundwater recharge by intercepting water before it reaches the groundwater system. It does this by trapping rainwater on leaves, branches and ground litter, from which the water evaporates, as well as through the process of evapotranspiration whereby water is pumped out of the soil by the root system and transpired (breathed) through the leaves.
Native vegetation is adapted to take advantage of any available water. It can use most of the water entering the soil profile from rainfall, allowing only a small portion to enter the groundwater system. Native perennial species require water for growth all year and have deep roots that absorb much of the water present in the surrounding soil. For example, the roots of an eucalypt can extend 30 to 40 metres below the ground, where as the roots of most agricultural plants extend for less than 2 metres.
Native vegetation is often replaced with crops that have shallow roots and shorter growth cycles. This results in more water entering the ground water system. The amount of leakage into the groundwater system under current farming systems is greater than that of native vegetation.
The amount of leakage in cropping areas varies depending on rainfall and cropping practices, and for agroforestry, depends on tree spacings.
The clearing of native vegetation from catchments, particularly in groundwater recharge areas, is the primary cause of the hydrological disturbances that lead to salinity problems. But there is often a significant time lag between the clearing and development of dryland salinity.
Native species such as salt bush, mallee and mulga have adapted to cope with salt stress. In some areas, salt bush and mallees have been used to remediate areas affected by salinity. In other areas, planting or regeneration of native vegetation and perennial pastures have been encouraged to reduce groundwater recharge. However, land managers should seek professional advice about salinity remedial work to ensure the best outcomes.
Page last updated: 26 February 2011