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Abstract:
Multi-factor experiments are often advocated as important for advancing terrestrial biosphere
models (TBMs), yet to date such models have only been tested against single-factor
experiments. We applied 10 TBMs to the multi-factor Prairie Heating and CO2 Enrichment
(PHACE) experiment in Wyoming, USA. Our goals were to investigate how multi-factor
experiments can be used to constrain models, and to identify a road map for model
improvement. We found models performed poorly in current ambient conditions; there was a
wide spread in simulated above-ground net primary productivity (range: 31-390 g C m-2 yr-1).
Comparison with data highlighted model failures particularly in respect to carbon allocation,
phenology, and the impact of water stress on phenology. Performance against observations
from single-factors experiments was also relatively poor. In addition, similar responses were
predicted for different reasons across models: there were large differences among models in
sensitivity to water stress and, among the N cycle models, N availability during the experiment.
