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

72 Joe Walker and Paul Reddell
5. Restoring the hydrological properties of degraded old landscapes to reduce
water and nutrient leakage is a critical first step. This places the focus on
acquiring and using knowledge about the functional characteristics of plants,
for example, plant rooting strategies to improve resource availability, and
understanding mechanisms about changes to the water cycle and the role of
soil biota.
The following are examples of restoration issues on old landscapes from
a semiarid ecosystem and a tropical ecosystem where recognition and understanding
of retrogressive succession may have a profound impact on the success
and effectiveness of restoration activities.
4.3 Human-Induced Salinization in Southern Australia: A Symptom of
Changes to the Water Cycle of Old, Semiarid Landscapes
Across southern Australia, landscape degradation issues are dominated by the
widespread occurrence of secondary salinity (salinity that appears after disturbance),
water logging, soil acidification, and soil structural decline. In combination,
they greatly affect water quality in streams, terrestrial and aquatic
biodiversity, roads and other infrastructure, and reduce ecosystem goods and
services (Hatton 2002). Areas with a Mediterranean climate, characterized by
wet winters with low evaporation rates, are particularly affected (McFarlane and
Williamson 2002). All the degradation issues have a common link—changes to
the inputs, outputs, and storage of water following the removal of the native vegetation
for human activity. Secondary salinization is considered here as one aspect
of the inability of old landscapes to sustain productivity and recover following
broad-scale vegetation changes and in many cases inappropriate land uses.
Salt-affected soils occur extensively across Australia, and are estimated to
cover approximately one-third of the continent (Northcote and Skene 1972, NL-
WRA 2001). The origins of salt in weathered landscapes, halomorphic soils,
and salt lakes in Australia have been attributed first to long-term weathering
of rocks of marine or lacustrine origin (Blackburn 1976), and second to atmospheric
accessions of inorganic aerosols in rain or dry fallout of either ocean or
terrestrial origin over geological time (Allison et al. 1983, Herczeg et al. 2001).
The presence of appreciable amounts of salt in deeply weathered landscapes is
considered to be a relict feature because saline soils are surrounded by nonsaline
soils developed from fresh rocks (Gunn and Richardson 1979). Salinization of
landscapes thus occurred prior to denudation and has been supplemented by
atmospheric and aeolian inputs since these earlier geological times. Even before
European settlement in Australia in the late 18th century, salty outbreaks
in woodlands and forested landscapes were part of Australia’s environment.
In arid and semiarid Australia, evaporation considerably exceeds rainfall.
These areas are also characterized by low slopes with low hydraulic gradients
and hence a lack of lateral water movement. Vertical leaching and little lateral
movement have resulted in subsoil salt stores. Much of the salt is stored below
the root zone of trees. To become a problem for agricultural production or to
pollute streams, the stored salt has to be mobilized vertically or laterally. Since
European settlement in the late 18th century, extensive agricultural land-use
following tree clearing has induced major changes to soil hydraulic properties
of the thin soil mantle, and hence the water cycle generally. With less evapotranspiration
resulting from vegetation clearing, more water percolates beyond the