Restoring soil multifunctionality through forest regeneration in abandoned Amazon pasturelands

Abandoned pastures with degraded soil quality in the Amazon region often undergo succession to secondary forests. While aboveground responses to natural regeneration have been well investigated, the impacts on soil functioning are still poorly understood. Here we assessed how multiple soil functions respond to the natural regeneration of abandoned pastures in the Amazon, and how many years of forest regeneration are needed to recover soil multifunctionality. We measured key properties of the soil as proxy indicators of six soil functions: (1) support for plant growth, (2) C sequestration, (3) nutrient storage and availability, (4) resistance to degradation, (5) water and air flux regulation, and (6) biological activity along a 45‐year chronosequence of natural regeneration in northwestern Colombia, and then we calculated an index of soil multifunctionality. The results revealed significant changes in physical–chemical and biological soil indicators due to the reforestation, increasing soil multifunctionality. The largest effects were found for soil C sequestration, with a sub‐index value that was nearly two times higher after 15 years of regeneration, followed by biological activity and resistance to degradation functions that increased 1.4 and 1.3 times, respectively, after 15 years of regeneration. The overall index of soil functioning indicated a clear benefit of restoration, reaching 76% of its soil functioning capacity after 15 years of pasture abandonment. Thus, our findings provide empirical evidence that secondary forest succession can restore soils' capacity to deliver vital ecosystem services in the Amazon region, playing a critical role in ecosystem restoration.