Cartographie de la variabilité thermique des écosystèmes forestiers de l’Est algérien.

Abstract

Algerian forest patrimony is estimated at 4 million hectares, including forests, Scrub and brush. This forest is exposed to natural and anthropogenic hazards that cause severe degradation resulting mainly in continued regressive evolution and a substantial loss of wealth. Among the natural threats is the climate conditions and particularly the temperature of the environment in which forest ecosystems evolve. In addition to its action on life processes, on growth and on phenology of species, temperature can change also the biogeographic areas of ecosystems. In this study we analyzed the temperature to characterize the thermal environment of eastern Algeria and the effects of its variation on the dynamics and photosynthetic activity of forest ecosystems in this vast area. The used data is the temperatures for a period of 30 consecutive years (1982-2011) and spectral index (NDVI) which can detect the photosynthetic signal above the canopy. Statistical analysis of long temperature series reveals that the warming observed worldwide is already noticed in eastern Algeria. The majority of the wilayas exposed to this hazard, where the trend is more pronounced for the annual maximum temperature, may reach 3 °C/30years, an increase of 0.1C°/year. Thus, the estimate of thermal field for each pixel in eastern Algeria was realized by using Geostatistical methods based on multiple regression between temperature and the explanatory variables describing the relief. From these spatial data, the thermal limits have been defined for each forest species. Finally, the technical of GIS and satellite images allowed us to monitor the dynamics of forest vegetation, and to build maps that define the relationship between forest biomass and thermal parameters. These maps helped us to identify 901087 hectares where trees were very sensitive to changes in the average temperature, with a percentage of 53.9% of the total area of the studied forest ecosystems. Thus, the minimum temperature affects photosynthesis of forest species in an area of 852406 ha with 50.8% of the total forest area. This cartographic expression is effective, firstly for forestry in the discrimination of forest plots where the thermal factor is the limiting factor of productivity and secondly for decision makers to define the forest management strategies of country.