Environmental Engineering Reference
In-Depth Information
Native
System
Chronosequence
X
X
Time
Figure 15.6.
Idealised model for biotic or abiotic parameter (x) used to assess the
success of individual restoration measures benchmarked against a native, undisturbed
or other appropriately selected target systems. Time may be in years, decades or
centuries.
It must also consider generational change such as seeding and recruitment;
and the development of positive and negative functional attributes such as
pollination, herbivory and pathogens. Ultimately, these must be viewed in
terms of the ecosystem's resilience to perturbation such as storms and fire
(e.g., Smith et al.
2004
). An overview of some of the fundamental characteristics
of the developing forest ecosystems after bauxite mining is discussed in the
following sections. As well as above- and below-ground development of biotic
parameters, some key abiotic measurements will also be described and dis-
cussed. Many of these are shown as progressing towards a benchmark value
determined at a native or reference site (or sites) to give an indication of
putative success (or otherwise) of each criterion (
Fig. 15.6
).
The capacity to monitor the development of post-mining ecosystems is
apparent from the presence of mining companies alongside the restored sites
for many decades (e.g., Gardner & Bell
2007
). The restored forests after mining
are effectively potential long-term ecological research sites. Unfortunately,
while vegetation monitoring often takes place on the same sites over many
years, most of the true research completed on these systems has relied on space-
for-time substitution analysis (Pickett
1989
). While simple and convenient
(many sites of different age can be visited on the same day), this approach
suffers from several weaknesses in post-mining systems and elsewhere (Fleming
1999
). Primarily, these include the variability of soil, the differences in initial
growing seasons by restored land unit, the variability of available seed in a
given (previous seed collection) season, and final position in the landscape (in
relation to aspect, hydrology and so on). This effectively amounts to pseudo-
chronosequences, not true sequences through time at the same site; although
these are often treated the same in the literature ( Johnson & Miyanishi
2008
).
Therefore, in this chapter a chronosequence of sites is in reality a space-for-time
