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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

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

Jeffrey Q. Chambers
Lawrence Berkeley National Lab

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8 February 2017

Hurricane effects on dry tropical forests

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
Our 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, we predict the long-term forest structure and productivity will not be largely affected in relationship to storm intensity alone. Additionally, our results suggest that subtropical dry forests will remain resilient to hurricane disturbances.

Summary
For this study we 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 NPP between 32% and 50%. In contrast, increasing hurricane intensity did not create a large shift in the long-term average forest structure, net primary productivity (NPP), or annual carbon accumulation (ACA) from that of historical hurricane regimes, but produced 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. Our 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 FATES, which is being integrated into ALMv1 and used by the NGEE-Tropics Project.

Contacts
(BER PM)

Dan Stover and Dorothy Koch
Daniel.Stover@science.doe.gov  (301-903-0289) and Dorothy.Koch@science.doe.gov (301-903-0105)

(PI Contact)
Jeffrey Q. Chambers
Lawrence Berkeley National Lab
jchambers@lbl.gov

William J. Riley
Lawrence Berkeley National Lab
wjriley@lbl.gov

Funding
DE-AC02-05CH11231 as part of their Next Generation Ecosystem Experiment-Tropics (NGEE-Tropics) and Accelerated Climate Modeling for Energy (ACME) programs.

Publication
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. Environ. Res. Lett. 12; 025007 (2017). 
Special Issue: “Focus on Tropical Dry Forest Ecosystems and Ecosystem Services in the Face of Global Change”

NGEE-Tropics and ACME


Fig.1 Shifts in six carbon components compared to historical hurricane regimes (control), with the total accumulation switching to positive (i.e. sink) in the bottom panels.

(figure also used in highlight slide)

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