Agriculture Reference
In-Depth Information
temperate forests (Bornebusch, 1930; Dunger, 1964; Saulnier and Athias-Binche, 1986)
with biomasses of 8-20 g f wt They are consistent inhabitants of litter layers in
tropical forests and woodlands where their populations may vary from mean values of
a few tens
(e.g.,
26 ind. weighing 5.7 g f wt in Miombo woodland, Dangerfield,
1990) to several hundred individuals weighing 0.3 to 4 g f wt (see,
e.g.,
Lavelle and
Kohlmann, 1984; Lavelle
et al.,
1981; Beck, 1971). In temperate and tropical grasslands,
populations are generally limited to a few tens per square metre (see for example, Persson and
Lohm, 1977; Athias
et al.,
1974) with a low biomass of 0.1 g f wt to 0.30 in moist
savannas at Lamto (Côte d'Ivoire) and 0.6 in tropical pastures of Mexico (Lavelle
et al
., 1981).
Soil and litter-dwelling Diptera larvae vary widely in size with small individuals,
e.g.,
in the families Chironomidae or Ceratopogonidae, of a few millimetres long and large
Tipulidae or Bibionidae which may attain three centimetres. They often have strongly
aggregated distributions and are only present in litters for a few months until they become
adults. They are seasonally important components of tundra soils with densities of
100-1000 ind. in most sites. The highest densities have been recorded in temperate
forests (especially in moder and mor humus types) where densities of several thousand
ind. are common (see,
e.g.,
Mollon, 1982; Petersen and Luxton, 1982). Maximum
values of 12,000 (Healy and Russell-Smith, 1971) and even 370,000 individuals per
have been found (Deleporte, 1981). Densities in temperate grasslands and tropical
environments rarely exceed a few tens of individuals
Biomasses may be as high as 16-40 g f wt
in temperate forests and tundra sites;
most data however range between 0.5 and 5 g
in these environments (Petersen and
Luxton, 1982).
Arachnida are the most abundant group of predators. Most values are in the range
20-200 ind. and maximum densities of 400-800 ind. have been recorded in
temperate forests with a mor or moder type of humus. Biomasses are modest and rarely
exceed 0.20 to 0.30 g f wt
Chilopoda have densities of a few tens of individuals. and biomasses of less
than 1 g f wt with maximum values in forests rather than grasslands and in temperate
rather than tropical ecosystems.
4.4
Determination of Soil Faunal Communities
Soil faunal communities differ markedly in their toxonomic and funtional diversities at all
scales of observation. These latter may vary from broad latitudinal gradients of temperature,
to regional mosaics of different soils, vegetation and land-use and down to a single soil pro-
file (see
e.g.,
Petersen and Luxton, 1982). Such variation results from population response to:
(i) local environmental constraints represented by a suite of hierarchically-organised
climatic and edaphic factors (see section IV.1.2.2), (ii) phylogenetic and biogeographical
constraints, and (iii) their interactions with other soil organisms, especially micro-organisms.
Soil organisms, especially the invertebrates, differ from those of other strata within
ecosystems in that they are exposed to unique sets of limiting factors. They tend to
be more closely constrained by external environmental factors and the limitations of
their own digestive systems than,
e.g.,
vertebrates or insects living in the aerial part of
