Shifts in Biomass and Productivity for a Subtropical Dry Forest in Response to Simulated Elevated Hurricane Disturbances

The Science

Caribbean tropical forests are subject to hurricane disturbances of great variability. In addition to natural storm incongruity, climate change can alter storm formation, duration, frequency, and intensity. This model-based investigation assessed the impacts of multiple storms of different intensities and occurrence frequencies on the long-term dynamics of subtropical dry forests in Puerto Rico. This is the first attempt to model hurricane effects for dry forests of Puerto Rico—a unique, overlooked, and threatened biome of the world.

The Impact

Project results revealed that more frequent storms led to a switch in simulated carbon accumulation from negative (i.e., source) to positive (i.e., sink), with coarse woody debris and leaf production being major carbon components that should be included in disturbance modeling. While there is evidence that hurricane intensity has been increasing in the Atlantic Basin over the past 30 years, team researchers predict the long-term forest structure and productivity will not be largely affected in relationship to storm intensity alone. Additionally, project results suggest that subtropical dry forests will remain resilient to hurricane disturbances.

Summary

For this study, the project used a previously validated individual-based dynamic vegetation gap model, and developed a new hurricane damage routine parameterized with site- and species-specific hurricane effects. Increasing the frequency of hurricanes decreased aboveground biomass by between 5% and 39%, and increased net primary productivity (NPP) between 32% and 50%. In contrast, increasing hurricane intensity did not create a large shift in the long-term average forest structure, NPP, or annual carbon accumulation (ACA) from that of historical hurricane regimes, but it did produce large fluctuations in biomass. With an increase in the frequency of storms, the total ACA switched to positive due to shifts in leaf production, annual litterfall, and coarse woody debris inputs, indicating a carbon sink into the forest over the long term and major carbon components that should be included in disturbance modeling. Project results suggest that subtropical dry forests will remain resilient to hurricane disturbance. However, carbon stocks will decrease if future climates increase hurricane frequency by 50% or more. These results, and the new disturbance damage routine, are being considered for DOE’s new dynamic vegetation model, Functionally Assembled Terrestrial Ecosystem Simulator (FATES), which is being integrated into the Accelerated Climate Modeling for Energy (ACME) Land Model version 1 (ALMv1) and used by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project.

Principal Investigator(s)

Jeffrey Q. Chambers
Lawrence Berkeley National Laboratory
[email protected]

William J. Riley
Lawrence Berkeley National Laboratory
[email protected]

Funding

DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and Accelerated Climate Modeling for Energy (ACME) program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science.

References

Holm, J.A., S.J. Van Bloem, G.R. Larocque, and H.H. Shugart. “Shifts in biomass and productivity for a subtropical dry forest in response to simulated elevated hurricane disturbances.” Environmental Research Letters 12(2), 025007 (2017). [DOI:10.1088/1748-9326/aa583c].