Tree performance and root-zone salt accumulation in three dryland Australian plantations

Doubts exist about the effectiveness of establishing trees near saline discharge areas on farmland to manage dryland salinity. These centre on low rates of water uptake from saline water tables, salt accumulation in tree root zones and the consequent poor growth and survival of trees. Despite this, trees still survive in many plantations established adjacent to saline discharge areas and land-holders often favour such locations, as they do not compete for arable land such as that occurs with plantings in recharge areas. Tree performance and salt accumulation were assessed in three experimental plantations established adjacent to saline discharge areas 20-25 years ago. These were all in the 400-600 mm rainfall zone of south-western Australia. Mean soil salinity, within 1 m of the surface, ranged from 220 to 630 mS m(-1), while permanent ground-waters occurred within 2-5 m of the surface and had electrical conductivities ranging from 175 to 4150 mS m(-1). The study confirmed the low growth rates expected for trees established over shallow, saline water tables in a relatively low rainfall environment, with estimated wood volumes in Eucalyptus cladocalyx, E. spathulata, E. sargentii, E. occidentalis and E. wandoo of between 0.5 and 1.5 m(3) ha(-1) yr(-1). Values of up to 3 m(3) ha(-1) y(-1) were obtained on soils with low salinity (< 200 mS m(-1)). The excellent survival (> 70%) of several Eucalyptus species confirms that discharge plantations species can persist, despite increasing soil salinity. However, the long-term sustainability of such plantings (50-100 years) without broader landscape treatment of the present hydrological imbalance must be questioned.