Combining experiments, observations and modelling to assess the role of soil cation depletion on secondary forest regrowth in the Congo basin

Intensification of shifting cultivation practices across the Congo basin are causing a rise in secondary forest area across the African tropical belt. Nutrient exports during burning (e.g. ash pulses) and cultivation of the land (e.g. biomass export and nutrient leaching) are potentially limiting the regrowth potential of the secondary forests that reestablish after land abandonment, potentially putting a break on the C accumulation rates of these forests. Among the nutrients that are being exported from the land, cations (Ca, Mg, K) are expected to be particularly vulnerable, especially on the old, highly weathered soils that are characteristic for the majority of lowland tropical forests in the Congo basin. Past studies on forest chronosequence data have already shown that (1) the availability of cations in the soil declines over time, and (2) cations accumulate in woody biomass over time and might get lost from the system permanently when timber or fire wood is being extracted from the system.

In our study, we aim to integrate data from a large fertilization experiment and observations along a chronosequence of secondary forest stands to assess the role of cation depletion on forest regrowth in the Congo basin. Here, we aim to present our (1) preliminary data and first findings and (2) our approach to integrate these findings into a biogeochemical forest growth model PnET-BGC. Via model-based scenario analyses, we present potential impacts of cation limitation on forest regrowth in the Congo basin and discuss how management can conserve nutrients and sustain carbon uptake in regenerating tropical forests.