Geoscience Reference
In-Depth Information
(b)
Climate:
The climate is of the continental sahelian type characterized by two seasons: a
rainy season from June to September and a dry season from October to May. The
harmattan
, a continental sandy wind from northeast mostly hot and dry blows
during the dry season, whereas the monsoon, a south-west wind, both maritime
and humid blows during the raining season. The temperature is permanently
high except in the desert zones where the thermal variations are relatively
significant. The highest temperatures are reached in May and the minimum in
February.
(c)
Soils:
The soils, mostly sandy, are characterized by a general deficiency in organic
matter and phosphorus, a continuous decrease of fertility, a tendency to acidifi-
cation, a low capacity of water retention and a high sensitivity to hydraulic and
wind erosion. Furthermore, there is a trend to alkalinization and salinization
around the hydro-agricultural areas and basins.
(d)
Vegetation:
By virtue of its spatial extent the country encompasses various climatic regimes
and physiographical units that give rise to a wide variety of ecological zones.
These zones range from lush forest vegetation in the south to Guinea savanna
in the middle belt region, Sudan savanna in the north and Sahelian vegetation in
the extreme northern part of the country. Of these ecological zones, the Sudan
and Sahelian regimes are most vulnerable to climatic and human pressures. The
decreasing aridity pressure gradient from north to south established four large
zones which are superimposed on the east-west oriented bands. The last two
(sahelian zone and soudano-sahelian zone) are home to 80 % of the population.
1. The Saharan zones are characterized by a discontinuous shrub-steppe. Ri-
parian vegetation forms thickets of
Acacia
spp. and palm trees (
Hyphaene
thebaica
) along water flows and sewage areas. The steppe is dominated by
Acacia erhenbergiana
in Irhazer and Tadress areas.
2. The sahelo-saharan zones are dominated by pseudo-steppes.
Acacia raddi-
ana
,
A
.
Senegal and Commiphora africa
are found on the sandy sub strata
which covers the biggest part of the Nigerien sahel whereas
Acacia nilotica
,
Balanites aegyptiaca
,
Maerua crassifolia etc
. are more adapted to muddy
soils.
3. In the sahelian zones, the vegetation takes the form of bushy savanna where
the dominants are
Acacia albida
,
Acacia Senegal
,
Borassus aethiopium
,
Hyphaene thebaica
,
Combretum glutinosum
etc. These areas are agro-
pastoral and are highly populated.
4. Finally, the soudano-sahelian zone which has forestry coverage of wooded
savanna. In these areas plantings of the Family
Combretaceae
dominate but
other species such as
Butyrospermum parkii
,
and Parkia biglobosa
are also
present.
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