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6.1 Revegetation with Deep-Rooted Perennials
The use of perennial vegetation to recover dryland salinity has been postulated as
the principal means of control since the opposite (clearing) was first observed in
Western Australia in the 1900s to be responsible for salinisation of water supplies
for steam trains (Wood 1924 ). Indeed, the first reclamation of the impact of rising
groundwater on stream salinity resulted from the prevention of further clearing and
ringbarking and complete reforestation of the small area that had been cleared in
Helena catchment (George et al. 1997 ). However, it was not until the 1980s that
active experimental programs began to investigate the impact of partial reafforesta-
tion as a management measure for control of stream salinity in the Wellington Dam
catchment.
In a review of empirical data derived from extensive tree plantings in 46 dis-
charge areas and 33 recharge areas in the agricultural region of Western Australia,
George et al. ( 1999 ), came to different conclusions. They concluded that trees were
better planted in recharge, rather than discharge, areas, and ‘... generally only
extensive plantings, perhaps influencing as much as 70–80 % of the catchment, will
lead to significant catchment scaled reductions in water tables...’. Further, George
et al. ( 1999 ) also showed that planting in discharge areas are often ineffective ‘... to
allow reclamation of saline areas, because the response in groundwater levels is
rarely greater than 10–30 m from the planted area’.
From an eco-hydrological approach, Hatton and Nulsen ( 1999 ) stated that
‘empirical and theoretical analyses suggest that however vegetation is managed in
the landscape, effective water balance control will be achieved only at a leaf area
index approaching that of the natural state, indicating revegetation of most or all
parts of the catchment with either trees or plants with similar ecohydrological char-
acteristics as trees’.
More recently, Bennett and George ( 2008 ) reviewed watertable and salinity dfata
collected from 24 sites on 15 farms planted since 1990 to various deep-rooted tree
species at varying combination of blocks, strips, belts and geometries (5 % to 90 %).
Their evaluation concluded that only at the highest percentage of catchment planted
(> 70–98 %), did trees impact groundwater levels to a significant degree (2–6 m
reduction over < 20 years). Importantly for agriculture, the area required to recover
the famers saline land was at least 5–10-times the area affected – a major disincen-
tive to plant non-commercial tree crops.
6.2 Engineering and Drainage
Recovering saline land using agricultural drainage in the context of irrigation sys-
tems has been evaluated for a considerable period of time (George et al. 1997 ).
Drainage options such as the use of open, tile, and other subsurface drains (mole
drains, tube drains), and groundwater pumping are cited in the literature as effective
D.J. McFarlane et al.