The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 332

studies have relied on inter-site comparison with only indirect evidence that
the sites were at different stages in the same succession. Studies of soil
microbial succession with genuine chronosequences are rare. In the case
of the post-fire chronosequence, the values of C mic :C total and qCO 2 for
the L layers were both greater for the 1957 than for the 1976 fire sites
(Table 4.15.2). This is the only sensible comparison that can be made in
the context of succession as no O horizon had developed at the site of the
fire in 1976. These observations offer only partial support for the proposals
outlined above of Insam and Domsch (1988), Insam and Haselwandter
(1989) and Anderson and Domsch (1986). It is difficult to isolate the
influence of time from those of diversity and quality of plant litter inputs
and other factors that affect soil microorganisms. For example, Wardle
(1993) reported that increases in qCO 2 at late successional sites were due
to physiological stress on the organisms and, in a comprehensive critique
of the qCO 2 parameter as an indicator of disturbance and ecosystem
development, Wardle and Ghani (1995) found no convincing evidence that
qCO 2 could be interpreted unambiguously in the context of succession.
There was indirect evidence in the form of the relative concentration
of C in larger particle size fractions that soil animals, other important
members of the decomposer community, were either less active or less
abundant in the burned soils compared with the unburned soil (Haslam
et al ., 1998). This is not an unexpected observation, but little can be
inferred directly and further work will be required to understand the
post-fire ecology of soil and litter invertebrates, which both Whelan (1995)
and Ahlgren (1994) describe as being poorly understood and the responses
of surviving and recolonizing populations as being highly variable.
Conclusions
We have provided an estimate for the rates at which organic matter
reaccumulates in soils after serious fires. This is important information
because one of the predictions of environmental change is increased
frequency of hot, dry summers in the temperate and circum-boreal
latitudes, which may lead to increased incidence of fires at sites of terrestrial
C storage. We have also provided preliminary information about the
post-fire succession which suggests that understanding of the successional
development of microbial communities is far from complete.
Acknowledgements
We are grateful to NERC for a postgraduate studentship to SFIH and to
the National Trust for site access.