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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #343455
Title: Assessing the impact of parameter uncertainty on modeling grass biomass using a hybrid carbon allocation strategy

Author
item Reyes, Julian Jon
item TAGUE, CHRISTINA - University Of California
item EVANS, R. - Washington State University
item ADAM, JENNIFER - Washington State University

Submitted to: Journal of Advances in Modeling Earth Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2017
Publication Date: 1/17/2018
Citation: Reyes, J.T., Tague, C., Evans, R.D., Adam, J.C. 2018. Assessing the impact of parameter uncertainty on modeling grass biomass using a hybrid carbon allocation strategy. Journal of Advances in Modeling Earth Systems. 9(8):2979-3115. https://doi.org/10.1002%2F2017MS001022.
DOI: https://doi.org/10.1002%2F2017MS001022

Interpretive Summary: Grasslands provide important agricultural products such as dairy and meat, and also support the communities in and around these areas. We use computer modeling to examine how energy from sunlight is partitioned between above and belowground portions of grass biomass (i.e. carbon allocation). We found that grasses require a dynamic carbon allocation strategy that changes over time, but that also takes into account plant growth and possible resource (i.e. nutrient, water) limitations. The HYBRID allocation strategy was developed and appropriately simulates biomass at several grassland sites. A parameter sensitivity analysis was also performed to examine how biomass responds to different parameter values used in the model. Shifts in parameter sensitivity, or importance, indicate where future parameterization should be focused to appropriately represent eco-hydrologic processes in our ecosystem model.

Technical Abstract: Grasslands play an important role in feeding the growing human population by supporting dairy and livestock production. The purpose of this paper was to improve the representation of carbon (C) allocation processes in ecosystem models, and to understand the sensitivity of simulated grass biomass to model parameters, providing guidance for future environmental change research. We used the Regional Hydro-Ecologic Simulation System to compare estimates of above and belowground biomass for C allocation strategies based on plant growth, resource use, and a newly developed HYBRID approach that integrates the first two allocation schemes. Observed values of biomass at seven grassland sites are used to compare performance of these three allocation strategies. Partial ranked correlation coefficients are then calculated to assess parameter importance and sensitivity under current and future climate conditions. We found that both resource use and plant growth play a role in simulating dynamic C allocation in grass biomass over time, indicating the need for the HYBRID approach to capture grassland C allocation. Parameter importance was site-specific under increased temperatures, enhanced carbon dioxide, and changed precipitation. Site-specific parameter importance also yielded insight into limiting resources (i.e. energy, moisture) at sites and subsequent effects on ecological processes like photosynthesis and allocation. This work increases our understanding of C allocation in ecosystem models related to grasses, and guides what model parameters may require further research.