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

Authors

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

Institutions

Lawrence Livermore National Laboratory, Livermore, CA

Abstract

Tropical forests account for over 50% of the global terrestrial carbon (C) sink and 29% of global soil C, but the stability of C in these ecosystems under a changing climate is unknown.

Recent work suggests moisture may be more important than temperature in driving soil C storage and emissions in the tropics. However, data on belowground C cycling in the tropics is sparse, and the role of moisture on soil C 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 C stocks and radiocarbon (¹⁴C) values of profiles from over 40 sites spanning 12 pantropical regions. The sites represent a large range of moisture, spanning 710 to 4200 mm 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 C stocks, with smaller C stocks and younger soil C 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. Researchers are exploring the influence of controlling factors in manipulation experiments and constrained gradients of precipitation, soil type, root inputs, geomorphology, land use, and disturbance on C storage and longevity through collaborative site-specific studies.