This work was completed on the study of the southern slope scrublands （matorrals） of Tlemcen region in the northwest of Algeria （Western Algeria）. These scrublands are under various states of degradation, made up ...This work was completed on the study of the southern slope scrublands （matorrals） of Tlemcen region in the northwest of Algeria （Western Algeria）. These scrublands are under various states of degradation, made up of Quercus ilex, Juniperus oxycedrus, Thymus ciliatus, Rosmarinus officinalis. The problems sought in this study are to give the actual position of vegetable cover and in particular that of the formations to matorrals currently existing in the southern slope of the area of Tlemcen, while being based on the phytoecological aspect of the vegetable groupings which constitute this inheritance. Sampling is the first phase of work based on the analysis of the spatial variations of the structure and composition floristic and considering the nature of the problem to be treated, the authors considered to be useful to use the method Zuricho Montpeli6raine developed at the point by Braun-Blanquet, the method usually used consists to collect all the plant species and to make the list of the species on a small square of surface 100 m2 （have it minimal）. The floristic readings （150 on the whole） were taken according to the method of Braun-Blanquet. Our results show that there exists a therophytisation marked by a general invasion of annual species as show us as the synergistic action of the aridity and the anthropic action generated important modifications on the level of the vegetation in the dynamic direction. This advanced degradation leads a steppisation which results in a substitution of the elements of the matorrals by species more adapted much the xericity.展开更多
Cedar forests area in northeastern Algeria （Aures） is decreasing by the massive tree mortality. In some localities more than 95% of the trees have recently died （e.g. Boumerzoug in Belezma National Park）. Three re...Cedar forests area in northeastern Algeria （Aures） is decreasing by the massive tree mortality. In some localities more than 95% of the trees have recently died （e.g. Boumerzoug in Belezma National Park）. Three reported episodes of massive tree mortality in 1880, 1980, and 2000 were attributed to drought at least as the triggering factor. Our main objective was to reconstruct drought events that could be linked to Atlas cedar tree mortality using tree-ring series. We developed a Cedrus atlantica tree-ring width chronology in Chelia with a reliable period spanning from 1502 to 2008. Based on the relationship between chronology indices and instrumental precipitation data, we reconstructed total October-June precipitation. Dry events were identified using a threshold of 90% of the October-June mean instrumental precipitation. The unique drought event of 3-year period （1877-1879） could explain the tree mortality occurred in 1880. In terms of severity and frequency of droughts, the later half of the twentieth century seems to be the worst and may be responsible for the recent tree mortality.展开更多
文摘This work was completed on the study of the southern slope scrublands （matorrals） of Tlemcen region in the northwest of Algeria （Western Algeria）. These scrublands are under various states of degradation, made up of Quercus ilex, Juniperus oxycedrus, Thymus ciliatus, Rosmarinus officinalis. The problems sought in this study are to give the actual position of vegetable cover and in particular that of the formations to matorrals currently existing in the southern slope of the area of Tlemcen, while being based on the phytoecological aspect of the vegetable groupings which constitute this inheritance. Sampling is the first phase of work based on the analysis of the spatial variations of the structure and composition floristic and considering the nature of the problem to be treated, the authors considered to be useful to use the method Zuricho Montpeli6raine developed at the point by Braun-Blanquet, the method usually used consists to collect all the plant species and to make the list of the species on a small square of surface 100 m2 （have it minimal）. The floristic readings （150 on the whole） were taken according to the method of Braun-Blanquet. Our results show that there exists a therophytisation marked by a general invasion of annual species as show us as the synergistic action of the aridity and the anthropic action generated important modifications on the level of the vegetation in the dynamic direction. This advanced degradation leads a steppisation which results in a substitution of the elements of the matorrals by species more adapted much the xericity.
文摘Cedar forests area in northeastern Algeria （Aures） is decreasing by the massive tree mortality. In some localities more than 95% of the trees have recently died （e.g. Boumerzoug in Belezma National Park）. Three reported episodes of massive tree mortality in 1880, 1980, and 2000 were attributed to drought at least as the triggering factor. Our main objective was to reconstruct drought events that could be linked to Atlas cedar tree mortality using tree-ring series. We developed a Cedrus atlantica tree-ring width chronology in Chelia with a reliable period spanning from 1502 to 2008. Based on the relationship between chronology indices and instrumental precipitation data, we reconstructed total October-June precipitation. Dry events were identified using a threshold of 90% of the October-June mean instrumental precipitation. The unique drought event of 3-year period （1877-1879） could explain the tree mortality occurred in 1880. In terms of severity and frequency of droughts, the later half of the twentieth century seems to be the worst and may be responsible for the recent tree mortality.
