Vol. 35 – 2009 - Ecologia Mediterranea - Université d'Avignon et des ...

NOURY BENABADJI, RÉDDA ABOURA, FATIMA ZOHRA BENCHOUK
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Through a comparative diachronic study of the
phytosociological statements, the authors
attempt a floristic characterization approach of
a steppic ecosystem of Lygeum spartum L.
The comparison of the two periods the floristic
tables (1991 and 2005) enabled us to notice that
the number of inventoried species, the rate of
average covering of the vegetation fell. The frequency
of Noaea mucronata thorny species and
toxic Atractylis serratuloides species increased
whereas that of Lygeum spartum and Artemisia
herba-alba regressed. In addition we raise the
appearance of Peganum harmala and disappearance
of Stipa tenacissima.
The pastoral pressure and the severe climatic
conditions explain this regressive dynamic of
Lygeum spartum steppic population.
The study reveals the vital role of anthropic
action on the damage of the route fround in
the steppe of western Algeria. Its regeneration
seem to be prevented by graze and the seeds.
Some pratices of farwing, as the use of the tractor
with plough of several discs its crumbles and
sprays the sandy soil on the one hand and the
oder hand, the complete vegetal destruction.
Abridged version
The steppic ecosystems, in Algeria, live under
a double threat, In one hand, a livestock load
in a constant growth, and in the other hand,
the random and mechanized exploitation that
leads to the damage of fragile ground.
The climatic changes, an inappropriate use of
the ground, the bad agricultural practices, the
density of the growing population, the economic
pressure and land regime modification
that contribute to the damage spread natural
resources.
The region of Hassi-Mellah belongs to the
Mediterranean climate, the thermal amplitude
(M-m = 37 oC) the place in a continental climate
in the sense of Debrach (1953). The pluviothermic
climate grams of Emberger
replaces the bioclimatic air of Hassi Mellah
steppe of Lygeum spartum in an arid bioclimate
characterized by a cold winter. The dryness
period, according to the ombrothermic
diagrams of Bagnouls and Gaussen reaches
9 mouths, on the other hand, it is less intense
on the mounts of Mekaidou and Sidi Djilali.
The steppe of Lygeum spartum in somes
places between Magoura and El Aricha
occupy wide expenses.
The regeneration of steppic population seen
to be prevented by graze and the seeds. Some
pratices of farming as the use of the tractor
with plough of several discs its crumbles. The
cereal farming spreads over the high steppic
plains between El Aricha, El Aouedj and
Hassi Mellah as well as on the foot mountain
in the south Djebel Mekaidou.
In the dry environment and the present-day
exploitation conditions by men, this results
everywhere by a continuous and regressive
steppic ecosystem evolution, leading, most of
the time, to a standardization of the vegetation.
Through a diachronic comparative study of
the phytosociological statements, the authors
attempt a floristic characterization approach
of a steppic ecosystem of Lygeum spartum.
The comparison of the floristic tables of the
two periods (1991 and 2005) show:
• a quantitative decrease of listed species (69
to 27);
• a rate decrease of medium recovery in % of
the vegetation, it decreases from 20 to 5%;
• decrease of Lygeum spartum and Artemisia
herba-alba species frequency, and the disappearance
of Stipa tenacissima;
• concerning the biological kinds, the percentage
of therophytes go from 68.11% in
1991 to 59.26% in 2005 that is to say a relatively
weak decrease of 9.85%. An increase
of chamaephytes percentage from 2.57%;
• concerning the biogeographical kind,
Mediterranean element still the most dominant
with 37.68% in 1991 and 37.04% in
2005. The species of Ibéro-mauritaniens origin
decrease (from 15,95% en 1991 to
3,70% in 2005). The north African endemic
elements are no more represented on the
floristic inventory of 2005.
From the phytogeographical point of view, the
analysis points out to a definite reduction of
the vegetation cover and to the notable presence
of saharo arabics.
This facies of Lygeum spartum presents actually
an impoverish floristic procession which
is subjected to a strong anthropic pressure,
and it is regressing.
This northbound rise of xeric species is due
to the denudation of the ground surface.
The recommendations for this area that has
objective to start a dynamics in this area are
on priority protecting and valorising the local
potentialities in this steppic ecosystem with
Lygeum spartum.
ecologia mediterranea – Vol. 35 – 2009