Linking Restoration and Ecological Succession (Springer ... - Inecol

74 Joe Walker and Paul Reddell
production per year as well as impacting on roads, buildings, and other infrastructures.
About 10% of the rural lands in Western Australia are affected by
salinization and this figure could double in the next few decades (George et al.
1997). In southeastern Australia about 5% of rural lands are salt affected (NL-
WRA 2001). Generally, salinization resulting from local groundwater systems
has a lesser impact than those from regional systems.
The broad impacts of land-use on the water cycle across landscapes since
European settlement are summarized by Williams et al. (2001) as follows:
Rainfall (P) = ET + DD + RO + IF + GWD + SBWS
� ET – evapotranspiration has decreased due to lower leaf area (LAI) values of
the vegetation when summed on a yearly basis (trees replaced by annual crops)
� DD – deep drainage (recharge or leaching) has increased as shown by
increasing groundwater pressures in salinized areas, but the change in water
amount is a small fraction of the total water balance and is hard to measure or
model
� RO – surface run-off (streamflow) has increased due to soil structural
changes that reduce soil permeability and surface soil storing capacity
� IF – interflow water that moves laterally down slope within the surface soil
has decreased due to a shallower soil A-horizon and soil structural decline
� GWD – ground water discharge has increased as evidenced by increased
areas of salinity and waterlogging
� SBWS – soil water storage has decreased in the unsaturated soil profile
(reduced in depth due to erosion and less soil organic matter) and less biological
water is stored in vegetation—that is, the surface soils are drier overall.
The key mechanisms operating in these old systems that originally stored
water and maintained soil profile integrity have been disrupted. The overall
changes in the water cycle following tree removal are a shift toward desertification,
i.e., a drier landscape, which is a consequence that has yet to be
widely accepted. That disturbed landscapes are drier than the original presents
an apparent paradox—drier surface soils but rising water tables. Williams et al.
(2001) suggest several mechanisms to explain this apparent paradox. These
include an increase in preferred water flow pathways at a range of scales from
micropores to hill slopes (termed holeyness) and a reduced capacity to store
water due to shallower soil A-horizons. Extensive tree planting to reduce the
area affected by salinity is widely adopted in Australia as a restoration method
but at least initially, this tends to dry out the landscapes even more. An alternative
is to develop restoration strategies that increase storage of soil moisture at
the surface and release water slowly to the root zone.
Given the context is restoration within salinized agriculturally productive
landscapes, the desirable end points of restoration actions can be stated as:
1. A mosaic of vegetation types that restore the hydrological functioning of the
soil and at the same time maintain economic viability.
2. Improved goods and services from the production landscape—water quality
and quantity with less export of saline water, and increased wildlife
habitat.
What knowledge is needed and what tools are available to restore salinized
landscapes to more productive agricultural land? We need to know how to