344
Pilar Andres, Eduardo Mateos and Carlos Ascaso
L layer (16 in L; 29 in both F+H and S). In the L layer, soil arthropods tend to
be randomly distributed. On the one hand, the relatively large gaps between
fresh-litter leaves facilitate animal movements. On the other, the seasonal
pattern of leaf-fall and the horizontal transport of litter by wind promote the
distribution at random of the microhabitats able to be colonized by soil
fauna (Garay 1985).
24.2.3 Seasonal Pattern
Mediterranean soil climate includes summers with water deficit, wet and cold
winters, and wet and warm autumns and springs. Litter endures strong daily
and seasonal climatic variations. Temperature of the L layer in Montseny
ranges from 28 DC in August to 0 DC in January. After summer rains and under an intense sunshine, its water content can drop in a few hours from saturation to 2%. The maximum fall of holm oak leaves, rich in aliphatic and
aromatic compounds unpalatable for the mesofauna, occurred in our study
from June to September. In autumn and winter, the plant litter is leached by
rain and loses tannins and phenols. The following summer, humification
starts and the litter, previously attacked by fungi and bacteria, becomes
palatable to the arthropods.
The litter acts as a buffer to the underlying soil layers. The humus layers
are relatively protected from the daily climatic variations, but undergo a seasonal fluctuation in water content. In spring and autumn, water availability
and warm temperatures enhance the growth of fungi that mycophagous arthropods use as an essential part of their diet. Less-fluctuant environmental
conditions prevail in the mineral soil, in which the biological activity is low
and the water content is moderate and much less temporally variable than in
the forest floor.
In Mediterranean soils, water is the most limiting environmental factor. At
Montseny, population parameters (such as density, relative abundance, and
indices of spatial distribution) of most mesofaunal species tend to vary in
parallel with soil water availability, though correlations with soil water content were significant only for some species (Table 24.2). Water surplus is less
Table 24.2. Montseny. Mesofaunal species, all of them oribatid mites, having significant linear
correlation coefficients (r) between water content in the litter layer and species density in this
layer, aggregation Index of Lexis (AI), and Usher Index of vertical distribution (DV). Maximum
n = 182 (26 sampling dates x seven spatial replicates)
Species
Density
Aggregation (AI)
Vertical distribution (DV)
Eueremaeus granulatus
0.77*
0.52
0.75*
Xenillus tegeocranus
0.84*
0.44
0.73*
Tectocepheus velatus
0.79*
0.76*
0.62
Chamobates cuspidatus
0.79*
0.75*
0.77*
Genus Oppia
0.70*
0.71*
0.32
* P < 0.001.
Pilar Andres, Eduardo Mateos and Carlos Ascaso
L layer (16 in L; 29 in both F+H and S). In the L layer, soil arthropods tend to
be randomly distributed. On the one hand, the relatively large gaps between
fresh-litter leaves facilitate animal movements. On the other, the seasonal
pattern of leaf-fall and the horizontal transport of litter by wind promote the
distribution at random of the microhabitats able to be colonized by soil
fauna (Garay 1985).
24.2.3 Seasonal Pattern
Mediterranean soil climate includes summers with water deficit, wet and cold
winters, and wet and warm autumns and springs. Litter endures strong daily
and seasonal climatic variations. Temperature of the L layer in Montseny
ranges from 28 DC in August to 0 DC in January. After summer rains and under an intense sunshine, its water content can drop in a few hours from saturation to 2%. The maximum fall of holm oak leaves, rich in aliphatic and
aromatic compounds unpalatable for the mesofauna, occurred in our study
from June to September. In autumn and winter, the plant litter is leached by
rain and loses tannins and phenols. The following summer, humification
starts and the litter, previously attacked by fungi and bacteria, becomes
palatable to the arthropods.
The litter acts as a buffer to the underlying soil layers. The humus layers
are relatively protected from the daily climatic variations, but undergo a seasonal fluctuation in water content. In spring and autumn, water availability
and warm temperatures enhance the growth of fungi that mycophagous arthropods use as an essential part of their diet. Less-fluctuant environmental
conditions prevail in the mineral soil, in which the biological activity is low
and the water content is moderate and much less temporally variable than in
the forest floor.
In Mediterranean soils, water is the most limiting environmental factor. At
Montseny, population parameters (such as density, relative abundance, and
indices of spatial distribution) of most mesofaunal species tend to vary in
parallel with soil water availability, though correlations with soil water content were significant only for some species (Table 24.2). Water surplus is less
Table 24.2. Montseny. Mesofaunal species, all of them oribatid mites, having significant linear
correlation coefficients (r) between water content in the litter layer and species density in this
layer, aggregation Index of Lexis (AI), and Usher Index of vertical distribution (DV). Maximum
n = 182 (26 sampling dates x seven spatial replicates)
Species
Density
Aggregation (AI)
Vertical distribution (DV)
Eueremaeus granulatus
0.77*
0.52
0.75*
Xenillus tegeocranus
0.84*
0.44
0.73*
Tectocepheus velatus
0.79*
0.76*
0.62
Chamobates cuspidatus
0.79*
0.75*
0.77*
Genus Oppia
0.70*
0.71*
0.32
* P < 0.001.