Model and Inventory Perspectives on the Role of Forests in the Global Carbon Cycle: Results from the Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP)

Abstract:

Forests play a significant role in the global climate system in large part through their uptake and storage of atmospheric carbon. Biomass inventories provide valuable constraints on annual to decadal changes in forest carbon stocks through periodic, repeated measurements. However, this information offers limited utility for attribution of the major drivers and process-level mechanisms that determine forest carbon dynamics. A better understanding of these mechanisms is needed to project future forest carbon cycle dynamics, which requires the use of process-based modeling for attribution of and sensitivity to the major drivers.

Here we compare and analyze recent estimates of the carbon budget of the world's forests based on national-level resource inventories against a suite of process-based model simulations run with a common protocol for formal inter-comparison. Our analysis of the model simulation experiments from the Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP) suggests a large uncertainty in carbon cycle responses to these drivers, traceable primarily to the wide range in model structure relative to whether and how they represent the impacts of forest growth, management, disturbance and land use change. Although our study illustrates the benefits in retaining independence among the inventory and modeling estimates for comparison and benchmarking, progress toward a better understanding of the role of forests in the current and future global carbon cycle can also be made by more formally integrating these alternative but complementary scaling approaches.