Variability of Organic Carbon Stocks in Forest and Agricultural Soils in Ecuador: A Systematic Review

The knowledge of soil organic carbon (SOC) stocks is essential for the sustainable management of forest and agricultural ecosystems. The objective of this review was to collect and compare the published values of SOC of the main soil orders and land-use systems of Ecuador, as well as to evaluate their variability as a function of site and altitude. A systematic review was carried out following the PRISMA protocol, analyzing 22 studies obtained from the Scopus and Web of Science databases between 2000 and 2025. For the primary synthesis, SOC stocks were harmonized to a common 0–30 cm depth; layer-specific values were summed, when possible, while non-harmonizable and deeper-profile data were excluded from the main comparison. Histosols and Andisols showed the highest SOC stocks (126–245 Mg C ha−1), whereas Inceptisols, Alfisols, and Entisols in coastal and Amazonian lowlands generally showed lower values (18–96 Mg C ha−1). The analysis also revealed a marked geographical bias towards the Andean region and a relatively recent focus on humid climate areas. Overall, the distribution of the SOC showed a marked spatial heterogeneity controlled by soil, climatic, and land-use factors, which highlights the need to conserve the Andean band to promote agroforestry on lands intervened to maintain Ecuador’s carbon stocks.