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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Model-Guided Field Experiments: Ecosystem CO2 Responses in an Australian Eucalypt Woodland

Anthony Walker

Highlight

13 September 2016

Multimodel a priori predictions for ecosystem CO2 responses in interaction with nutrient and water limitation.

The Science 
Quantitative model projections were made for the recently established Eucalyptus Free-Air CO2 Enrichment (EucFACE) experiment in Australia. Model simulations were designed to evaluate the experiment data as they are collected and to identify key measurements that should be made to discriminate among competing model assumptions.

The Impact
Knowledge of the causes of variation among models is now guiding data collection in the experiment, with the expectation that the guided experimental data collection will optimally inform future model improvements.

Summary
A major uncertainty in Earth System models (ESMs) is the response of terrestrial ecosystems to rising atmospheric carbon dioxide (CO2) concentration, particularly in nutrient-limited environments. The EucFACE experiment, established in a nutrient- and water-limited woodland, presents a unique opportunity to address uncertainty in ESMs, but it can best do so if key model uncertainties have been identified in advance. The research team applied seven representative vegetation models to simulate a priori possible outcomes from EucFACE. Simulated responses to elevated CO2 of annual net primary productivity (NPP) ranged from 0.5% to 25% across models. The simulated reduction of NPP during a low-rainfall year varied even more widely than the CO2 response—from 24% to 70%. Key processes where assumptions caused disagreement among models included nutrient limitations to growth, feedbacks to nutrient uptake, autotrophic respiration, and the impact of low soil moisture availability on plant processes.

Contacts
BER Program Manager
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)
Jared.DeForest@science.doe.gov (301-903-1678)

Principal Investigator
Anthony Walker
Environmental Sciences Division, Climate Change Science Institute
Oak Ridge National Laboratory
Oak Ridge, TN 37831
walkerap@ornl.gov

Funding
The Primary Industries Adaptation Research Network (PIARN), set up under the National Climate Change Adaptation Research Facility (NCCARF), supported this project and travel for the participants to Sydney, Australia. Support via EucFACE as an initiative supported by the Australian government through the Education Investment Fund and the Department of Industry and Science, in partnership with the University of Western Sydney. Research support from the Australian Research Council. Other support from the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy (DOE) Office of Science and the European Community's Seventh Framework Programme (FP7 2007–2013) under grant agreement n° 238366 (Greencycles II).

Publications
Medlyn, B. E., et al. "Using models to guide field experiments: A priori predictions for the CO2 response of a nutrient- and water-limited native Eucalypt woodland." Global Change Biology 22(8), 2834–2851 (2016). [DOI:10.1111/gcb.13268].

Related Links
Data

FACE Model-Data Synthesis project, funded by DOE Office of Science, BER, supported participation by Anthony Walker, Richard Norby, and Xiajuan Yang. Primary funding sources were Australian and are listed on the highlight document. CLM4.0 and CLM-CNP models were used in this study. 

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