La quantification du carbone emmagasiné dans les écosystèmes forestiers et de son équivalent en CO₂ constitue un impératif pour une estimation fiable de la contribution de ce puits de carbone dans la limitation des émissions de gaz à effet de Serre. La présente étude vise dans un premier temps, par une étude de terrain, à évaluer le volume de bois sur pied et à estimer la quantité de carbone contenue dans les parties aériennes et racinaires, tout en déterminant le facteur d’expansion et de conversion de la biomasse (FECB) spécifique du cèdre de l’Atlas (Cedrus atlantica Manetti) situé dans la zone du Moyen Atlas central. D’autre part, les résultats obtenus ont été comparés à ceux provenant de l’utilisation des paramètres génériques du Groupe d’experts Intergouvernemental sur l’évolution du climat (GIEC) en 2006. Le volume de bois sur pied et la biomasse aérienne ont été déterminés en utilisant des tarifs de cubage et des modèles de biomasse développés à partir des mesures directes du poids sec et du volume sur 30 arbres échantillonnés et prélevés dans chaque forêt de la zone d’étude. Le volume et la biomasse aérienne ont été évalués respectivement à 3 321 284 m³ et à 1 521 153 t de matière sèche. Le FECB, déterminé par le rapport entre le volume et la biomasse, est de 0,36 tMS/m³, valeur inférieure à celle estimée par le GIEC (0,55 tMS/m³). La fraction de carbone (FC), issue de la calcination des échantillons de bois prélevés, est de l’ordre de 0,5643 tC/tMS. Elle est supérieure à la valeur donnée par le GIEC (0,51 tC/tMS). Au final, la quantité de carbone contenue dans l’écosystème étudié est de 858 387 t de matière sèche contre 931 620 t estimées à partir des paramètres du GIEC.

Forest resources in the Ourika watershed are subject to several anthropogenic and climatic degradation factors. As for the human factor, this degradation of forest resources is explained by the bad practices exercised by the local population expressed by the cutting of live wood, carbonization, and overgrazing. In terms of the climatic factor, the decrease in the amount of rainfall and the increase in temperature contribute to the exacerbation of the degradation of these resources. In order to better understand the evolution of plant cover in a changing climate context, this study highlights an assessment of the impact of climate change on forest dynamics based on a process-based model at the forest landscape scale which makes it possible to simulate the changes according to growth, succession, disturbances (fire, wind, insects, etc), forest management, and land use change. This analysis is based on the use of the LANDIS-II model and the PnET-succession extension. Projections of the dynamics of forest communities are made using climate projections from the Japanese global circulation model adopted by Morocco (model for interdisciplinary research on climate – earth system models) and this by adopting the two climate scenarios , representative concentration pathways 4.5 and 8.5. The results obtained highlight the spatial distribution of the ecosystems studied after 100 years with a quantitative evaluation of the total average biomass of these resources as a function of climatic disturbances. In general, the estimated total biomass will decline over the coming years under the joint effect of the climate change and the aging of forest stands, while on the other hand, the distribution of potential areas for species settlement remains independent of the effect of these climate changes.

Organic matter is essential in forest ecosystems to maintain the structural stability of the soil. Following soil assimilation, it evolves in two opposite ways: mineralization and humification. This leads to the formation of a wide variety of substances that, evolve according to very different kinetics. This work involved studying the stability of organic matter in the soils of forest ecosystems: Atlas cedar, holm oak, zeen oak, and maritime pine. This study was performed on representative samples of the upper soil layer (0-30 cm) of the different ecosystems, using a biochemical fractionation technique. Results from the extraction of humic substances showed that humin is the main component (53 and 75%), followed by humic acids (19 and 34%) and fulvic acids (6 and 16%). These findings indicate stable carbon abundance and good sequestration of this element in the soils studied. Zeen oak and maritime pine have the most stable soil organic matter with a humification ratio of 4.30 and 4.10, respectively. Furthermore, the formation of humic substances is closely linked to the presence of clay that favors the formation of the clay-humic complex, making this material difficult to access by microorganism soils and therefore more resistant to decomposition. Ultimately, the studied soils have a stable organic matter which increases the dwell time of carbon in the soil. Such a result can be proved in further research, by using appropriate techniques like stable isotopes (13C).

This study compares three common methods for measuring Soil Organic Carbon (SOC) in Morocco's Middle Atlas forests: the Walkley-Black (WB) method, the Loss on Ignition (LOI) method, and the Total Organic Carbon analysis by catalytic oxidation coupled with Non-Dispersive Infrared (NDIR) detection (TOC-CO-NDIR). Soil samples (n = 90) were taken from the upper organo-mineral horizon at depths of less than 30 cm of three major forests located in the Middle Atlas of Morocco, under different forest species such as Atlas cedar, green oak, Zeen oak, and maritime pine). The results show that SOC values ranged from 4.30 to 6.33%. Indeed, the TOC-CO-NDIR method showed the highest variability (standard deviation 3.22%), demonstrating its sensitivity to diverse SOC concentrations. In contrast, the LOI method showed a higher mean value of 6.33% and moderate variability, with a standard deviation of 2.35%, suggesting that it measures not only organic carbon but also other volatile compounds. The WB method displayed a mean of 4.55% with a standard deviation of 2.01%, indicating lower variability and greater stability of measurements. Correlation analysis showed a moderate and significant correlation between the TOC-CO-NDIR and LOI methods (r = 0.46, p = 0.031), while the correlation between TOC-CO-NDIR and WB was negligible (r=-0.0015, p = 0.946), and a weak correlation between WB and LOI (r = 0.32, p = 0.149). The analysis of variance (ANOVA) revealed significant differences between the methods (p = 0.0227). The Root Mean Square Error (RMSE) values show that the LOI method is the most similar to the WB method, followed by LOI and TOC-CO-NDIR, and then WB and TOC-CO-NDIR, indicating LOI and WB provide the most consistent results for practical soil carbon analysis. A comparative cost analysis highlights the practicality of the LOI and WB methods due to their low equipment and operational costs, in contrast to the TOC-CO-NDIR method, which requires expensive instrumentation and specialized personnel. Highlights • The study evaluates three methods, WB, LOI, and TOC-CO-NDIR for SOC quantification. • TOC-CO-NDIR shows the highest variability (SD = 3.22%), whereas LOI and WB exhibit better consistency. LOI moderately correlates with TOC-CO-NDIR (r = 0.46, p = 0.031). • LOI offers a balance between precision, cost, and practicality, while WB is cost-effective but less precise, and TOC-CO-NDIR provides high precision but is expensive and requires specialized equipment.