Soil Arthropods
349
colonization from neighbouring ecosystems. The ability for self-movement
or for using transport vectors (as phoretic Acari or Pseudo scorpionida do) is
then of great importance.
The effect of fire on Collembola was studied in detail at Prades. Immediately after fire, Collembola disappeared from the ashbed. Density decreased
99% in the organic layers and 26% in the upper mineral soil, but increased
60% in the deeper mineral layer. Eighty-six per cent of the species in the organic layers disappeared, but the number of species doubled in the deeper
mineral layer. The vertical pattern of specific diversity was similar.
One year after the fire, the depth-integrated density of Collembola was
still 87% lower than in the unburnt plots, and the number of species was 17%
lower. Most Collembola (80%) were then collected in the mineral soil. The
litter-dwelling species were absent or were collected in a very low density.
Some of the species characteristic of forest ecosystems, such as Isotomiella
minor and Protaphorura pro lata, disappeared from the burnt plot, whereas
the density of some species that characterize open ecosystems, such as Metaphorura affinis and Onythiurus minutus, increased. Some pioneer species
specialized in burnt soils, such as Willemia scandinavica, Paratullbergia callipygos and Entomobrya quinquelineata, appeared during this first year. Two
years after fire the density and number of species of Collembola remained
lower than in the unburnt plots, but the vertical distribution of animals was
similar to the pre-fire situation.
There is no agreement about the short- and long-term effects of fire on
soil fauna (Huhta et al. 1967; Majer 1984; Saulnier and Athias-Binche 1986;
Neumann and Tolhurst 1991). Estimates of the post-fire populations' recovery time range from 2 to 7 years, but other authors state that the hypogeal
fauna of sclerophyllous forest soils remains unaltered when fires are neither
frequent nor intense, and even that the variations caused by fire are smaller
than the spatial and temporal natural fluctuations of the soil communities. In
Prades, 2 years was probably not enough to complete the faunal recovery in
the soil, despite the occurrence of some factors favouring the recovery, such
as the small plot area and the proximity of an unburnt holm oak forest.
24.4 Epigeal Arthropods
24.4.1 Density, Abundance and Trophic Characteristics
Data on the epigeal soil fauna come from pit-fall traps in the permanent plot
located in the holm oak forest at La Castanya (Montseny; Chap. 2). Half
(49%) of the collected arthropods (8% of the dry weight biomass) are mainly
hypogeal, but they are collected in pit-fall traps when they emerge to the
surface under favourable climatic and trophic conditions (Table 24.5).
349
colonization from neighbouring ecosystems. The ability for self-movement
or for using transport vectors (as phoretic Acari or Pseudo scorpionida do) is
then of great importance.
The effect of fire on Collembola was studied in detail at Prades. Immediately after fire, Collembola disappeared from the ashbed. Density decreased
99% in the organic layers and 26% in the upper mineral soil, but increased
60% in the deeper mineral layer. Eighty-six per cent of the species in the organic layers disappeared, but the number of species doubled in the deeper
mineral layer. The vertical pattern of specific diversity was similar.
One year after the fire, the depth-integrated density of Collembola was
still 87% lower than in the unburnt plots, and the number of species was 17%
lower. Most Collembola (80%) were then collected in the mineral soil. The
litter-dwelling species were absent or were collected in a very low density.
Some of the species characteristic of forest ecosystems, such as Isotomiella
minor and Protaphorura pro lata, disappeared from the burnt plot, whereas
the density of some species that characterize open ecosystems, such as Metaphorura affinis and Onythiurus minutus, increased. Some pioneer species
specialized in burnt soils, such as Willemia scandinavica, Paratullbergia callipygos and Entomobrya quinquelineata, appeared during this first year. Two
years after fire the density and number of species of Collembola remained
lower than in the unburnt plots, but the vertical distribution of animals was
similar to the pre-fire situation.
There is no agreement about the short- and long-term effects of fire on
soil fauna (Huhta et al. 1967; Majer 1984; Saulnier and Athias-Binche 1986;
Neumann and Tolhurst 1991). Estimates of the post-fire populations' recovery time range from 2 to 7 years, but other authors state that the hypogeal
fauna of sclerophyllous forest soils remains unaltered when fires are neither
frequent nor intense, and even that the variations caused by fire are smaller
than the spatial and temporal natural fluctuations of the soil communities. In
Prades, 2 years was probably not enough to complete the faunal recovery in
the soil, despite the occurrence of some factors favouring the recovery, such
as the small plot area and the proximity of an unburnt holm oak forest.
24.4 Epigeal Arthropods
24.4.1 Density, Abundance and Trophic Characteristics
Data on the epigeal soil fauna come from pit-fall traps in the permanent plot
located in the holm oak forest at La Castanya (Montseny; Chap. 2). Half
(49%) of the collected arthropods (8% of the dry weight biomass) are mainly
hypogeal, but they are collected in pit-fall traps when they emerge to the
surface under favourable climatic and trophic conditions (Table 24.5).