Warming experiments are increasingly relied on to estimate plant responses to global climate change1,2. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing3,4,5. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.
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This work was conducted as part of the Forecasting Phenology Working Group supported by the National Center for Ecological Analysis & Synthesis (EF-0553768), with additional support from National Science Foundation grants DBI-0905806, IOS-0639794, DEB-0922080 and the Natural Sciences and Engineering Research Council of Canada CREATE Training Program. Special thanks to the many data managers, including G. Aldridge, P. Huth, D. Inouye, G. Johansson, A. Miller-Rushing, J. O’Keefe, R. Primack, S. Smiley, T. Sparks and J. Thompson. We thank M. Ayres, L. Kueppers, D. Moore and M. O’Connor for comments on earlier drafts.
This file contains the raw sensitivities that are shown in Figure S2c, which are from the PEP725 database and which are discussed in the Supplementary Data, Methods and Results.
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Scientific Reports (2018)