Beta diversity and fallow length regulate soil fertility in cocoa agroforestry in the Northern Ecuadorian Amazon

Shifting agriculture (SA), a common practice in tropical areas, involves fallow phases between crop cycles, enabling the recovery of plant communities and soil fertility. However, the reduction of fallow length adversely influences forest structure and topsoil properties. The diversification in tree composition is considered to favour suitable levels of soil fertility in agroforestry systems (AFSs). To test this idea, we investigated whether minimum tree species replacement (β- diversity) between AFSs with reduced fallow length in SA decreases nutrient loss in soils sustaining cocoa (Theobroma cacao) agrosystems. Quantitative analyses revealed that substitution of arboreal species in cocoa AFSs correlated with shifts in soil nutrients. The replacement of fewer arboreal species in AFSs under reduced uncultivated land buffers detrimental effects of intensive land-use on soil productivity. Thus, the dominance of certain tree species is essential to maintain adequate levels of nutrient cycling dynamics with extended fallow length. Similarly, other arboreal species affect soil acidity. In conclusion, the combination AFSs-SA embodies a harmonious farming system that produces food supplies and other goods for human well-being while preserving plant diversity and natural ecological corridors for native flora and fauna. •Beta diversity correlates with shifts in soil nutrients in the Northern Ecuadorian Amazon.•Absence of fallows in shifting agriculture appears to homogenize tree composition and soil properties in cocoa agroforestry.•Upper tree composition and fallow length strongly explains changes in soil properties.