Carbon Fraction Distribution in Forest Soils and Leaf Litter Across Vegetation Types in El Chico National Park, Mexico

Soils are the largest terrestrial carbon (C) reservoirs and play a key role in regulating the global C cycle and supporting essential ecosystem services. Soil C sequestration is a viable strategy to reduce atmospheric CO2 concentrations and mitigate climate change. This study quantified soil C fractions and litter C stocks across five vegetation types in El Chico National Park, Hidalgo, Mexico (2015.55 ha): pine–oak, oyamel–oak, cedar, oyamel–Tlaxcal, and oyamel forests, all occurring under comparable climatic and edaphic conditions. Soil organic matter (SOM) was quantified as the organic fraction originating from decomposed plant and animal residues. No statistically significant differences (p > 0.05) were found among vegetation types for organic matter, total C, oxidizable C, or recalcitrant (non-oxidizable) C, indicating relative homogeneity across strata. Significant differences (p < 0.05) were detected in organo-mineral C (Cp) and poorly oxidizable C (Cdox), with oyamel–Tlaxcal and oyamel forests showing the highest values, respectively, suggesting enhanced potential for C stabilization and turnover. Oyamel forests stored 32.94% of total soil organic C and contributed disproportionately to park-wide C stocks given their dominance (85.6% of the total area). Leaf litter contained on average 6.60 Mg C ha−1, representing 13,302.63 Mg C and 48,836.8 Mg CO2 across the park. When integrated with soil C to 60 cm depth, total C and CO2 stocks reached 643,474.26 Mg and 2,361,566.66 Mg, respectively. These findings highlight the critical role of oyamel forests as the main carbon sink in the park and reinforce the importance of conserving these ecosystems as a nature-based solution for climate change mitigation.