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

82 Joe Walker and Paul Reddell
Soil organic carbon (%)
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sequences in lower montane rainforests on the Atherton Tablelands in North
Queensland (Reddell, Hopkins and Spain, unpublished). The original rainforests
of the Atherton Tableland were extensively cleared for agricultural development
in the early 20th century (Winter et al. 1987), but from the 1930s
until recently, many areas were abandoned for economic reasons. By interpreting
a sequence of aerial photographs of the region from the 1940s to the late
1990s, two replicated chronosequences of secondary rainforest succession on
each of the two soil types (that contrasted strongly in their inherent fertility)
were established. The secondary successional chronosequences were selected
to include five distinctive structural/seral categories of vegetation. These categories
were (1) herbland, (2) shrubland, (3) young secondary forest (approximately
18–25 years of regrowth since abandonment), (4) old secondary forest
(approximately 50–70 years of regrowth since abandonment) and (5) intact
rainforest that had been selectively logged but not cleared. The two soil types
for which the chronosequences were identified differed markedly in their chemical
and physical properties and in the structural type of rainforest community
that they were capable of supporting. The contrasting soil types were (1) an
old, highly weathered soil derived from Palaeozoic schists and phyllites and
(2) a young, highly fertile, weakly weathered soil developed from Quaternary
basaltic lavas. The two soils originally supported distinctive rainforest structural
types, a simple and a complex notophyll vine forest, respectively (Tracey
1982).
Aspects of the floristics, biological productivity, rates of nutrient cycling, and
nutrient acquisition strategies by plants were then compared across the stages
of rainforest succession on the young and old soils, revealing major differences
in the rates and trajectories of major processes and plant attributes between the
contrasting sequences (Fig. 4.6).
In the case of the succession on the young soil type, measures of ecosystem
function such as soil organic carbon, microbial biomass, and bulk density all
increased consistently and progressively along the chronosequence and in the
older secondary forests approached values in the comparable primary forest type
(i.e., there was a progressive succession; Fig. 4.6). Exchangeable cations and
various compositional and structural parameters, including species diversity,
average canopy height, and basal area, showed the same patterns. In contrast,
(a) (b) (c)
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Microbial carbon (g C g dry soil)
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5 10 20 80 Primary
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Soil bulk density (g cm -3 )
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5 10 20 80 Primary
Figure 4.6 Soil organic carbon (a), microbial biomass (as measured by microbial carbon) (b), and soil bulk density
(c) for rainforest successional sequences on young (solid line) and old soils (dotted line).
Years