# Congo Basin Carbon Cycle Responses to Global Change

## TL;DR

The Congo Basin remains a weak carbon sink despite environmental pressures, but its future depends on understanding climate, land use, and CO2 effects.

## Contribution

This is the first comprehensive assessment of Congo Basin carbon cycle responses to global change drivers.

## Key findings

- Congo Basin forests have limited responses to precipitation variability but declining stocks with rising temperatures and droughts.
- Land use changes reduce carbon stocks, while savanna fires provide nutrients that support carbon sequestration.
- CO2 fertilization may increase water-use efficiency, but its impact on biomass accumulation remains uncertain.

## Abstract

The Congo Basin and its contiguous forests harbor globally significant carbon stocks, estimated at 65 gigatons of C (GtC) above and belowground. Despite rising temperatures and intensifying droughts, they have remained a carbon sink, albeit weak: 0.26–0.50 GtC yr.−1 carbon uptake since 1980. However, these forests' carbon stocks and fluxes, including gross primary productivity, respiration, net primary productivity, and riverine carbon transport, remain poorly quantified. This limits understanding of the region's role in the global carbon cycle, its vulnerability to environmental change, and its potential as a long‐term carbon sink. We review and quantify Congo Basin and contiguous forest carbon stocks and fluxes and synthesize the current knowledge on how key global change drivers shape the region's carbon cycle. We find limited responses to long‐term precipitation variability, but declining stocks and fluxes in response to long‐term and increasing temperature and drought frequency. Land cover and land use changes, largely driven by small‐scale agriculture, logging, and agro‐industrial expansion, reduce carbon stocks, ecosystem structure and functioning, and animal‐mediated ecosystem services. In contrast, large‐scale savanna biomass burning delivers phosphorus and nitrogen to Congo Basin forests via cross‐equatorial winds, providing additional nutrients and supporting carbon sequestration. In situ studies suggest that CO2 fertilization has increased intrinsic water‐use efficiency, although its effects may be modulated by climate change, and its impacts on biomass accumulation remain uncertain. Legacy effects from historical land use and climate change likely shaped present‐day vegetation structure, yet their relative influence is unclear. High‐resolution carbon monitoring, improved remote sensing, and strengthened in situ measurement networks are needed to quantify the impacts of these key drivers and their interactions on the Central African carbon cycle. This is needed to inform conservation strategies and advance understanding of the region's future as a carbon sink under global change pressures.

Understanding the resilience of the Congo Basin carbon cycle in the face of current and future pressures requires a detailed understanding of its response to past and present drivers of change. Building on a pantropical framework of drivers and possible regional mechanisms for resilience, this review provides the first comprehensive assessment of Congo Basin carbon cycle responses to change, focusing mainly on the late 20th century to present. We first quantify and describe three components of the Congo Basin carbon cycle: (1) above‐ and belowground carbon stocks, (2) GPP, net primary productivity (NPP) and respiration (total, autotrophic, or heterotrophic), and (3) lateral carbon fluxes. We then synthesize current knowledge on the response of these components to the four drivers of change: climate change, land cover and land use change (LCLUC), carbon dioxide (CO2) fertilization, and legacy effects, as well as their interactions. We conclude by identifying priorities for future research.