2024 Abstracts

Tropical Forest Response to a Drier Future: Measurements, Synthesis, and Modeling of Soil Carbon Stocks and Age


Karis McFarlane* (mcfarlane3@llnl.gov), Kari Finstad, Nina Zhang, Allegra Mayer, Jennifer Pett-Ridge


Lawrence Livermore National Laboratory, Livermore, CA


Tropical forests account for over 50% of the global terrestrial carbon sink and 29% of global soil carbon, but the stability of carbon in these ecosystems under a changing climate is unknown. Recent work suggests moisture may be more important than temperature in driving soil carbon storage and emissions in the tropics. However, data on belowground carbon cycling in the tropics is sparse, and the role of moisture on soil carbon dynamics is underrepresented in current land surface models, limiting the ability to extrapolate from field experiments to the entire region. The team measured or attained data for soil carbon stocks and radiocarbon (14C) values of profiles from over 40 sites spanning 12 pantropical regions. Project sites represent a large range of moisture, spanning 710 to 4,200 millimeters of mean annual precipitation (MAP), and include Alfisols, Andisols, Inceptisols, Oxisols, and Ultisols. Researchers found a large range in soil 14C profiles between sites, and in some locations, the team also found a large spatial variation within a site. MAP explains some of the variation in soil 14C profiles and carbon stocks, with smaller carbon stocks and younger soil carbon in drier forests. However, differences in soil type contribute substantially to observed variation across the dataset and with constrained gradients in moisture and parent materials in Panama. The project compares measured soil profile 14C and carbon stock values to those modeled with the E3SM Land Model version 1 to demonstrate the utility of soil carbon and 14C for benchmarking.