106
Community Structure
changes in community structure are chiefly driven by seasonally varying climatic variables both in the unburned and the burned site. However, due to
the effect of fire on the structural properties of the habitats and the accompanying changes in climatic variables, the taxa in the burned site are more
evenly distributed throughout the year.
As has been shown, the long-term effect of fire on both numbers and community structure within regular seasonal changes is due to a reduction in
aboveground vegetation cover and litter, which in turn results in changes in
microclimatic conditions and food resources. Thus, no specific adaptations of
habitat selection are anticipated since the numerical recovery of fauna as well
as the restoration of the various communities depend on the recovery of
vegetation. In contrast, fire leads to broad climatic selection by inducing
stronger fluctuations in environmental variables. Indeed, species resistant to
sudden changes in their environment, such as diplopods, are equally good
colonisers of destroyed areas. In fact, diplopods (e.g. some Glomeridae and
Julidae) tolerate temperature changes in a range from -3 to about 50°C,
whilst, they can resist xeric conditions by conglobating. Although the overall
reproductive potential of diplopods is low, under favourable climatic conditions major recruitment to the population occurs every 3-4 years, corresponding with interannual climatic cycles. Long-lived diplopods evidently confront periods of limited resources after fire with their low numbers, whereas
population recovery follows restoration of the overstory vegetation and
accompanying improvements in micro climatic and food conditions after 3-4
years.
Reconstruction of aerial fauna takes place faster. Giliomee (1989, 1992)
recorded almost total destruction of aerial fauna in a fynbos after fire. Nevertheless, 7 months later 11 out of 12 species of grasshoppers had returned,
while five supplementary species were also recorded.
7.4.2
Grazing-Induced Structures
The organisation of oribatid and collembolan communities in a maquis formation on Mt Hortiatis was investigated by Asikidis and Stamou (1991) and
by Argyropoulou et al. (1994) respectively. Figure 7.7 shows the arrangement
of monthly samples of collembolan species on the plane of the first two axes
of a DCA biplot. Species composition changes drastically before and after the
dry period, and community structure in the dry period is entirely different
from that in the wet period. The seasonal effect on numbers of collembolan
species is so pronounced as to lead to bipolarity in community composition
rather than to a gradient in time. It is again evident that changes in numbers
as well as horiwntal organisation of the communities due to overgrazing lie
within the seasonal boundaries.
Community Structure
changes in community structure are chiefly driven by seasonally varying climatic variables both in the unburned and the burned site. However, due to
the effect of fire on the structural properties of the habitats and the accompanying changes in climatic variables, the taxa in the burned site are more
evenly distributed throughout the year.
As has been shown, the long-term effect of fire on both numbers and community structure within regular seasonal changes is due to a reduction in
aboveground vegetation cover and litter, which in turn results in changes in
microclimatic conditions and food resources. Thus, no specific adaptations of
habitat selection are anticipated since the numerical recovery of fauna as well
as the restoration of the various communities depend on the recovery of
vegetation. In contrast, fire leads to broad climatic selection by inducing
stronger fluctuations in environmental variables. Indeed, species resistant to
sudden changes in their environment, such as diplopods, are equally good
colonisers of destroyed areas. In fact, diplopods (e.g. some Glomeridae and
Julidae) tolerate temperature changes in a range from -3 to about 50°C,
whilst, they can resist xeric conditions by conglobating. Although the overall
reproductive potential of diplopods is low, under favourable climatic conditions major recruitment to the population occurs every 3-4 years, corresponding with interannual climatic cycles. Long-lived diplopods evidently confront periods of limited resources after fire with their low numbers, whereas
population recovery follows restoration of the overstory vegetation and
accompanying improvements in micro climatic and food conditions after 3-4
years.
Reconstruction of aerial fauna takes place faster. Giliomee (1989, 1992)
recorded almost total destruction of aerial fauna in a fynbos after fire. Nevertheless, 7 months later 11 out of 12 species of grasshoppers had returned,
while five supplementary species were also recorded.
7.4.2
Grazing-Induced Structures
The organisation of oribatid and collembolan communities in a maquis formation on Mt Hortiatis was investigated by Asikidis and Stamou (1991) and
by Argyropoulou et al. (1994) respectively. Figure 7.7 shows the arrangement
of monthly samples of collembolan species on the plane of the first two axes
of a DCA biplot. Species composition changes drastically before and after the
dry period, and community structure in the dry period is entirely different
from that in the wet period. The seasonal effect on numbers of collembolan
species is so pronounced as to lead to bipolarity in community composition
rather than to a gradient in time. It is again evident that changes in numbers
as well as horiwntal organisation of the communities due to overgrazing lie
within the seasonal boundaries.