biological diversity and tropical forests in tunisia - PART

3.3.2. Sebkhets and Chotts
Sebkhets are temporary wetlands, generally on salty soils, fed by
slightly to moderately saline runoff water. Most sebkhets are dry by late
summer, but some retain part of their water throughout the year. Chotts
are vast dry depressions that were lakes in the pleistocene age (?40rgac
1982). They are too large to be completely filled with runoff water, but
portions contain water in most years. The fauna and flora of chotts acd
sebkhets are similar, although the chotts have a hkgher percentage of
bare, dry ground.
Sebkhets and chotts occupy a significant area in Tunisia (almost 2
million ha) and they play an important role in moderating floodwaters,
trapping sediments and providing habitat for a variety of fauna. The
greatest concentration of sebkhets is in the Low Steppe region of easterc
Tunisia and near the southeast coastal region. Large chotts form a line
across south-central Tunisia from Gabes to the Algerian border.
Salice soils in the sebkhets and chotts restrict the vegetation
associations to salt tolerant species. Dominant species do cot vary
greatly among the chotts and sebkhets, although some secondary components
vary with soil, water and climatic conditions. A vegetatior. transect from
the center to the edge of a typical sebkhet or chott in summer would show
the following basic characteristic zonation (ORSTOM 1962):
Unvegetated center with very salty soils - often with salt crust
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Halopeplis amplexicaulis
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Halocnemum strobilaceum
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Arthrocnemm glaucum
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Limoniastrum sp.
Salsola cruciata
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Salsola tetrandra - Atriplex halimus
or Suaeda fruticosa
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Salsola vermiculata or Traganum nudatum
A low diversity of dominant vegetation species, most of which are
halophiles, does not favor diverse or abundant sedentary a~imal
populations in the chotts and sebkhets. The temporary cature of most
eebkhets restricts their use as wetland habitat during the seasons whec
they are dry. However, during the seasons when there is water, great
numbers of migrating and wintering waders and waterfowl feed and rest in
the chotts and sebkhets. Waterfowl feed on plants such as Potamogeton
pectinatus and filamentous algae in the larger, less saline sebkhets and
on invertebrates, typically Moina rectirostris,