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La régression des steppes méditerranéennes : le cas d’un faciès à Lygeum spartum L. d’Oranie (Algérie) The regression of the Mediterranean steppes: The case of Lygeum spartum L. facies in Oran region (Algeria) Résumé Les steppes à sparte occupent de vastes portions du territoire dans l’ouest algérien même si leur régression est évidente depuis le début du siècle dernier. Ces milieux semblent avoir subi des changements particulièrement rapides et intenses. Outre l’influence de la précarité climatique, on souligne l’effet fortement amplifié de la pression humaine dans le processus de dégradation du tapis végétal. Sur le plan bioclimatique, la région de Hassi Mellah (ouest algérien) appartient au climat méditerranéen continental dans un bioclimat aride à hiver froid. La période de sécheresse peut atteindre neuf mois. Les sols présentent une texture fine riche en sables, très pauvres en matière organique, la salinité est élevée, le pH est alcalin. Les auteurs à partir d’une étude diachronique comparative des relevés phytosociologiques tentent une approche de la caractérisation floristique d’un écosystème steppique à Lygeum spartum L. La comparaison des tableaux floristiques des deux périodes (1991 et 2005) nous ont permis de remarquer que le nombre d’espèces inventoriées et le taux de recouvrement moyen de la végétation ont diminué. La fréquence de Noaea mucronata espèce épineuse et de Atractylis serratuloides espèce toxique a augmenté alors que celle de Lygeum spartum et de Artemisia herbaalba a régressé. Par ailleurs nous relevons l’apparition de Peganum harmala et la disparition de Stipa tenacissima. Mots clés : Lygeum spartum L., steppe, bioclimat, anthropisation, étude diachronique, surpâturage, dégradation écosystémique. ecologia mediterranea – Vol. 35 – 2009 Noury BENABADJI, Rédda ABOURA et Fatima Zohra BENCHOUK BP119, Département de Biologie et Environnement, Faculté des Sciences, Université Abou Bekr Belkaid-Tlemcen, 13000 Algérie Adresse pour la correspondance : M. ABOURA Rédda, aredda78@yahoo.fr La pression pastorale et les conditions climatiques sévères expliquent cette dynamique régressive des peuplements steppiques à Lygeum spartum. Cette étude révèle le rôle primordial de l’action anthropique sur la dégradation des terres de parcours dans cette steppe de l’Algérie occidentale. Sa régénération semble être empêchée par le broutage et le piétinement des semis. Certaines pratiques culturales, telles l’utilisation de tracteurs à charrues polydisques émiettent et pulvérisent les sols à texture sableuse d’une part et la destruction totale de la végétation d’autre part. Abstract The steppes with sparte occupy large portions of the west Algerian lands even if their decrease is obvious since the beginning of the last century. This places seem to have suffered from the Quick and intense changes. As well as the influence unstable climatic, we have the much amplified effect of the human pressure in the process of the vegetal rug decrease. In the bioclimatic field, the region of Hassi-Mellah belongs to the Mediterranean and continantal climate in arid bioclimate characterized by a cold winter. The dryness period reaches 9 months. The soil of this facies of Lygeum spartum represents a texture full with sand, poor in organic matter, the salinity is raised, the Ph is basic. Keywords: Lygeum spartum L., steppe, bioclimate, anthropisation, diachronic study, overgrazing, ecosystemic degradation. 75
NOURY BENABADJI, RÉDDA ABOURA, FATIMA ZOHRA BENCHOUK 76 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
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