Effect of forest land use change on carbohydrates, physical soil quality and carbon stocks in Moroccan cedar area.

The present work was conducted to evaluate the carbon storage potential of Moroccan cedar forest and its vulnerability to transformations through deforestation and overgrazing. The present study took place in the Middle Atlas where is the most beautiful of Moroccan cedar forest (Cedrus atlantica). We considered three levels of degradation (Natural cedar, degraded cedar and cleared area). For each land use, we estimated carbon stocks in four reservoirs, i.e., aboveground biomass (trees, shrubs and herbaceous plants), belowground biomass (roots), necromass (litter and deadwood) and the soil. Various physico-biochemical characteristics (structural stability, bulk density, soil organic carbon and carbohydrates (neutral and uronic sugars)) were also evaluated. Carbon stocks were 395.37 Mg ha-1 for the natural cedar and 76.05 Mg ha-1 for the cleared area. Analysis of the ecosystem carbon stock distribution revealed that soil was the largest reservoir. The soil carbon stock varies from 46.4% to 93.5%, that of the biomass (aboveground and belowground) fluctuate between 4.3% and 52.7% and in the necromass it is between 0.8 and 2.2%. The conversion of natural forest into cleared area resulted in a deterioration of the soil physical quality (decrease of the percentage of water-stable aggregate by 36% and increase of bulk density by 57%). Also, natural forests have 25% and 50% more neutral sugars and uronic sugars respectively than the cleared area. The correlations established between carbohydrates and carbon stocks of the different reservoirs considered showed that the increase in neutral sugars is more explained by the aboveground biomass (R2 = 79%, P = 0.0013) and necromass (R2 = 85%, P = 0.0004). Otherwise, the soil carbon stock explained the most increase in uronic sugars (R2 = 99%, P = 0.0001). Neutral sugar can be an indicator of soil physical quality. Neutral sugars were responsible for 85% of the highly significant increase in soil structural stability and over 79% of the highly significant decrease in bulk density. Moreover, uronic sugars appear to be a good indicator of the richness in organic carbon of soils sampled since the increase of these sugars justified more than 90% of the increase in the soil organic carbon content.