Etude de la dynamique de l’enrésinement en Algérie Nord-orientale

Abstract

Several cork oak forests in the northeast of Algeria are subject to a coniferisation by the maritime pine, this forest dynamic that began in the 1980s is often cited as one of the degradation factors of the Algerian cork oak forests, but has never been studied. Our objective is to know the extent of the coniferization by a vegetation mapping, understand its dynamics and its determinants by a chorological mapping of slope, exposure, hydrography and burnt surfaces. Therefore, we applied a geomatics approach with field surveys. From the plant succession’s point of view, the invasion of a cork oak forest by the maritime pine is a regressive dynamic, the maritime pine being a pioneer specie for the cork oak forest. The hypothesis of a colonization from ecotones following a disturbance (eg: fire), seems to be the most plausible to explain its origin, and it agrees with the distribution of vegetation as a mosaic. The slope can favor the coniferization, the studied cork oak forests being mainly on steep and medium slopes, more prone to soil erosion, water deficit and air drying. The north-west, west and north exposures which are most affected by the coniferization, shows that the maritime pine can compete with the cork oak even on its preferred exposures. The chorology of the coniferization appears to be completely independent of the hydrographical network, his reject the hypothesis according to which the coniferization of the studied cork oak forests could progress along the alluvial zones by hydrochory. The role of the fire in particular and disturbances in general is evident as being the trigger for the regressive dynamic process (coniferization). The coniferization of cork oak forests by the maritime pine is a good illustration of the ""patch dynamics"" paradigm. The increase of fires and the degradation of environmental conditions can fovorize the coniferization or even the establishment of semi-desert vegetation by a regressive series. A good conservation of the cork oak forests invaded by the maritime pine could restart the sylvigenetic cycle allowing the reinstallation of the cork oak by a secondary succession.