Ecologia Mediterranea
Ecologia Mediterranea
Ecologia Mediterranea
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N. BOUCHENEB, S.S. BENHOUHOU<br />
70<br />
E1 Rhus tripartita-Olea europaea subsp. laperrinei community<br />
E2 Cassia aschrek-Panicum turgidum community<br />
E3 Tamarix gallica-Desmostachya bipinnata typical community<br />
E4 Tamarix aphylla-Farsetia ramosissima community<br />
E5 Acacia raddiana-Salvadora persica community<br />
E6 Leptadenia pyrotechnica-Chrozophora brocchiana community<br />
Figure 4 – Relevés spread of the whole data set along the first two axis.<br />
ies on desert vegetation (Abd El-Ghani &<br />
Amer 2003; Ali et al. 2000; Anthelme 2007;<br />
Benhouhou et al. 2003b; Dargie & El-Demerdash<br />
1991; Shaltout & Mady 1996; Springuel<br />
and Sheded 1991). The numerical analysis<br />
chosen is a correspondence analysis using<br />
ANAPHYTO (Brian 1991). The second stage<br />
of data analysis was the phytosociological<br />
study of the identified plant units via the association<br />
tables. These are considered as the<br />
basis for any syntaxonomical analysis. The<br />
only framework valid for the Algerian desert<br />
vegetation is the one proposed by Quézel<br />
(1965) and which has thus been considered in<br />
the present analysis. Among the four existing<br />
classes covering all the habitats encountered<br />
in this vast territory two classes were found:<br />
the Pergulario-Pulicarietea Quézel 1965 and<br />
the Asterisceto-Forsskaoletea Quézel 1965.<br />
We considered perennials to be the most<br />
important component in describing the vegetation<br />
units and treated annuals as companions<br />
usually characterised by erratic occurrence.<br />
The latter are of less importance as they<br />
reflect short-lived habitat conditions (Fossati<br />
et al. 1998).<br />
Results<br />
Axis 2<br />
Axis 1<br />
The correspondence analysis applied to the<br />
data matrix (190 relevés and 108 species)<br />
enabled the identification of six floristic<br />
groups (Figure 4). The high eigenvalues for<br />
the first two axes (axis 1: 0.58 and axis 2:<br />
0.45) suggest that two main gradients are at<br />
work. Analysis of the relevés spread along the<br />
first axis clearly indicates that an altitudinal<br />
gradient is responsible for the floristic distribution.<br />
Relevés close to the negative part of<br />
the first axis were taken at an altitude that<br />
varies between 1400 and 1600 m while those<br />
at the other end of the first axis were recorded<br />
between 800 to 900 m. Relevés plotted in the<br />
middle of the axis were taken at the intermediate<br />
altitude of 1200 m. The second axis<br />
shows a textural trend where relevés plotted<br />
towards the negative part of the axis were on<br />
coarse sand mixed with stones and those plotted<br />
at the other end had finer sand in their<br />
edaphic profile.<br />
From the 190 quadrats presented in the ordination,<br />
91 relevé “types” were chosen according<br />
to their floristic content to illustrate and<br />
discuss the six identified communities.<br />
ecologia mediterranea – Vol. 38 (2) – 2012