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CLAUDE J. GRENOT
and leaching, the mineral elements remain near the surface of the ground.
These soils have a good fertility potential when the water problem is
solved.
The desert soils have a certain microorganismic activity that includes
members of bacteria (especially those intervening in the nitrogen cycle),
microscopic algae, and fungi (Nègre, 1918; Killan and Feher, 1935, 1938;
Killian, 1944; Nicot, 1955, 1956; Rougieux, 1966). Where dead and decaying plants and animals are found, putrifying bacteria proliferate and
fertilize the soils. Biological phenomena such as nitrification occur here
in the same manner, but at a lesser intensity than in more favorable
climates.
The primordial factor for plants is the quantity of water available, and
this depends on the ability of the soil to store water and to make it available to the plant (involving porosity, imbibition, etc.). The dunes represent
a relatively humid environment—at least for the Sahara. Here evaporation
is important; water stays in the sand, in part, and does not leave as rapidly
as from other soil types. Thus water can be obtained by plants that are
adapted to dune life, especially those with long, deep roots. The water
is easily given up to the plants because it is not tied to the sand by imbibition as is the case with the clay soils.
The soil and the vegetation can offer shelter for the fauna, not because
of the shade and protection from the sun, but largely because of the microclimates created. During the day, no animal can exist around these tufts
of vegetation. However, in the morning, one can see numerous tracks
in the sand about them. F. Bernard (1953) has commented: "The least
plant concentrates around it a faunistic ensemble more abundant than any
analogous plant in the humid regions."
D. THE MICROCLIMATES
The ecological importance of microclimates in the Sahara is considerable. For many animals the microclimate in which they live is more important than the climate of the region (UNESCO, 1958). The propagation
of a species depends only indirectly on the general climate; it is tied to
the variable conditions of the substrata. Each animal lives in a microenvironment, of which the climate may be said to be a microclimate.
The microreliefs (sand under rocks, the rugged terraine, and the overhangs), the bushes, and the burrows, all minimize the physical factors of
temperature, aridity, light, and wind, yielding special microclimates (Kachkarov and Korovine, 1942). The stones on the regs can be a refuge for
arthropods such as scorpions, lepismantids, tenebrionid beetles, and mantids, the so-called Eremiaphila.
CLAUDE J. GRENOT
and leaching, the mineral elements remain near the surface of the ground.
These soils have a good fertility potential when the water problem is
solved.
The desert soils have a certain microorganismic activity that includes
members of bacteria (especially those intervening in the nitrogen cycle),
microscopic algae, and fungi (Nègre, 1918; Killan and Feher, 1935, 1938;
Killian, 1944; Nicot, 1955, 1956; Rougieux, 1966). Where dead and decaying plants and animals are found, putrifying bacteria proliferate and
fertilize the soils. Biological phenomena such as nitrification occur here
in the same manner, but at a lesser intensity than in more favorable
climates.
The primordial factor for plants is the quantity of water available, and
this depends on the ability of the soil to store water and to make it available to the plant (involving porosity, imbibition, etc.). The dunes represent
a relatively humid environment—at least for the Sahara. Here evaporation
is important; water stays in the sand, in part, and does not leave as rapidly
as from other soil types. Thus water can be obtained by plants that are
adapted to dune life, especially those with long, deep roots. The water
is easily given up to the plants because it is not tied to the sand by imbibition as is the case with the clay soils.
The soil and the vegetation can offer shelter for the fauna, not because
of the shade and protection from the sun, but largely because of the microclimates created. During the day, no animal can exist around these tufts
of vegetation. However, in the morning, one can see numerous tracks
in the sand about them. F. Bernard (1953) has commented: "The least
plant concentrates around it a faunistic ensemble more abundant than any
analogous plant in the humid regions."
D. THE MICROCLIMATES
The ecological importance of microclimates in the Sahara is considerable. For many animals the microclimate in which they live is more important than the climate of the region (UNESCO, 1958). The propagation
of a species depends only indirectly on the general climate; it is tied to
the variable conditions of the substrata. Each animal lives in a microenvironment, of which the climate may be said to be a microclimate.
The microreliefs (sand under rocks, the rugged terraine, and the overhangs), the bushes, and the burrows, all minimize the physical factors of
temperature, aridity, light, and wind, yielding special microclimates (Kachkarov and Korovine, 1942). The stones on the regs can be a refuge for
arthropods such as scorpions, lepismantids, tenebrionid beetles, and mantids, the so-called Eremiaphila.