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

Biomass/Height etc.
Max
Recovery
Impact
Chapter 4 Retrogressive Succession and Restoration on Old Landscapes 71
Impact
Progressive Regressive
approx. 140K years
Partial recovery
or collapse
Figure 4.1 In young landscapes after an impact the vegetation tends to return to the
original state, whereas on old landscapes vegetation will only partially recover or collapse
(modified from Walker et al. 2001).
escaped the direct effects of the Pleistocene glaciations that destroyed the Tertiary
landscapes and weathering mantles over much of the northern hemisphere.
In old landscapes, the residual products of weathering have formed thick soil
mantles generally lacking weatherable minerals and have low concentrations
of available plant nutrients. The extensive areas of lateritic soils in Australia,
and in the tropics generally are examples of this (Sanchez 1976). As secondary
minerals form in the weathering zone, there is an initial increase in available
plant nutrients, but this decreases rapidly as the supply of weatherable minerals
is depleted (Stark 1978, Walker and Syers 1976). With progressive weathering,
plant nutrient availability decreases, and plant species trend toward those
with more efficient mechanisms of nutrient capture and storage. Aboveground
biomass is reduced, the proportion of belowground biomass increases and physiological
and morphological adaptations are common (Lamont 1981, Walker et
al. 1987, Pate 1994). The system may be stable in its undisturbed state, but is
particularly vulnerable to disturbance as shown by a lesser ability to recycle nutrients
or retain water. An example is the failure of tropical rainforests on yellow
podzolic or lateritic soils to regenerate after clearing, burning, and agricultural
use (Sanchez 1976). The implication is that halting an inevitable decline after
disturbance may be impossible in old landscapes, and at best one has to settle
for a stable system state different from the original as a restoration end-point.
In summary, natural retrogressive succession has the following attributes:
1. A decline in ecosystem productivity and complexity occurs over millennia
due to processes associated with soil weathering, especially a decline in
nutrient availability and declines in a range of soil properties that affect the
water cycle.
2. The intact ecosystems of old landscapes are usually stable as the result of
the gradual development of adaptive plant physiological and morphological
traits.
3. Man-induced disturbances (clearing, burning, grazing, and farming) push
old systems quickly into further decline (new system states) and key system
functions may be lost permanently.
4. Restoration expectations (end-points) in old landscapes are different from
young landscapes and a stable system state different from the original state
may be the best outcome.