Ecologia Mediterranea
Ecologia Mediterranea
Ecologia Mediterranea
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N. BOUCHENEB, S.S. BENHOUHOU<br />
Introduction<br />
The most important studies on the flora and<br />
vegetation of the Ahaggar are those of Maire<br />
(1940), Quézel (1954; 1965; 1997) and Barry<br />
et al. (1972; 1981). The Ahaggar has a diversified<br />
flora estimated between 350 to 400<br />
species (Maire 1940; Quézel 1965; Quézel<br />
1997) which features several endemics (Olea<br />
europaea subsp. laperrinei (Batt. & Trab.)<br />
Cif., Myrtus nivellei (Batt. & Trab.), Lavandula<br />
antineae Maire) and relict trees (Pistacia<br />
atlantica Desf.). The vegetation in the<br />
Ahaggar is found in valleys, on wadis and<br />
nearby terraces that cut their way through the<br />
mountain massifs and outwash zones where<br />
underground sub-surface water flows are permanent.<br />
Phytosociological studies in the Ahaggar<br />
started with the work of Maire (1940) followed<br />
by in-depth studies undertaken by<br />
Quézel (1954) in the Ahaggar. Later, Quézel<br />
(1965) proposed a global syntaxonomical<br />
framework for the northern, north-western,<br />
central and southern Sahara. Further phytogeographical<br />
studies, with a particular focus<br />
on the vegetation of the In Salah and Tamanrasset<br />
regions, enabled Barry et al. (1981) to<br />
make a detailed analysis of the plant groupings<br />
belonging to the Acacia-Panicum desertic<br />
savannah.<br />
Figure 1 – Geographical localisation of Tamanrasset in the Ahaggar<br />
(Central Sahara).<br />
68<br />
More recent contributions to vegetation studies<br />
in the Ahaggar have explored areas of the<br />
range not previously investigated, such as<br />
Halem (1990) who describes the vegetation of<br />
two major wadis in the Tefedest and<br />
Abdelkrim (1992), who identified a new association<br />
Pistacia atlantica-Myrtus nivellei in<br />
the Taessa region. Further investigations in<br />
remote, relatively inaccessible sites south of<br />
Tamanrasset enabled Boucheneb (1999) to<br />
describe several plant groupings. Phytosociological<br />
studies of the region have therefore<br />
been sparse and, considering the vast territories<br />
covered by the Ahaggar, plant community<br />
description for the area is far from being complete.<br />
The objectives of the present work are<br />
to identify the major ecological gradients<br />
associated with the differentiation of several<br />
wadi plant communities related to different<br />
wadi types and to provide detailed descriptions<br />
of vegetation units sampled for the first<br />
time in the Tamanrasset region. The described<br />
plant communities are then put in a wider<br />
geographical context by comparing them with<br />
similar communities in other mountainous<br />
areas of the Saharo-Arabian belt.<br />
Study area and methodology<br />
Geology and geomorphology<br />
The Ahaggar, a vast territory in the centre of<br />
the Sahara, is located 2000 km south from the<br />
Algerian coast (Figure 1). The region covers<br />
450,000 km 2 of mainly mountainous nature<br />
with two major subareas: a metamorphic and<br />
igneous area in the central part of the Ahaggar<br />
and the Tassilian shield at the periphery<br />
(Fabre 1976). The central area consists of significantly<br />
younger rocks than the shield area<br />
and is characterised by several character<br />
regions, of which the most important are the<br />
Attakor culminating at the Mount Tahat with<br />
an altitude of 2918 m, the north-south aligned<br />
Tefedest (highest summit at 2400 m) and the<br />
Amadror, famous for its salt-flats (Lelubre<br />
1952).<br />
This basement complex has undergone several<br />
sedimentation cycles, the products of<br />
which have been cleared during successive<br />
subsequent erosion cycles. Within such a context,<br />
alluvia strewn on wadi beds hold shallow<br />
sub-surface water flow, which constitutes<br />
the main water resource in this area. The<br />
wadis sampled in the Tamanrasset region<br />
ecologia mediterranea – Vol. 38 (2) – 2012