title: Warming experiments underpredict plant phenological responses to climate change.
abstract: Warming experiments are increasingly relied on to estimate plant responses to global climate change. 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 leafing. 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.
authors.affiliation: Division of Biological Sciences, University of California San Diego, 9500 Gilman Drive 0116, La Jolla, California 92093, USA. wolkovich@biodiversity.ubc.ca
authors.forename: E M
authors.initials: EM
authors.lastname: Wolkovich
authors.forename: B I
authors.initials: BI
authors.lastname: Cook
authors.forename: J M
authors.initials: JM
authors.lastname: Allen
authors.forename: T M
authors.initials: TM
authors.lastname: Crimmins
authors.forename: J L
authors.initials: JL
authors.lastname: Betancourt
authors.forename: S E
authors.initials: SE
authors.lastname: Travers
authors.forename: S
authors.initials: S
authors.lastname: Pau
authors.forename: J
authors.initials: J
authors.lastname: Regetz
authors.forename: T J
authors.initials: TJ
authors.lastname: Davies
authors.forename: N J B
authors.initials: NJ
authors.lastname: Kraft
authors.forename: T R
authors.initials: TR
authors.lastname: Ault
authors.forename: K
authors.initials: K
authors.lastname: Bolmgren
authors.forename: S J
authors.initials: SJ
authors.lastname: Mazer
authors.forename: G J
authors.initials: GJ
authors.lastname: McCabe
authors.forename: B J
authors.initials: BJ
authors.lastname: McGill
authors.forename: C
authors.initials: C
authors.lastname: Parmesan
authors.forename: N
authors.initials: N
authors.lastname: Salamin
authors.forename: M D
authors.initials: MD
authors.lastname: Schwartz
authors.forename: E E
authors.initials: EE
authors.lastname: Cleland
mesh_terms: D016477:Artifacts; D017753:Ecosystem; D035264:Flowers / Q000254:growth & development / Q000502:physiology; D057232:Global Warming; D008954:Models, Biological; D010507:Periodicity; D063245:Plant Development; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology; D018521:Plant Physiological Phenomena; D010944:Plants / Q000145:classification; D015203:Reproducibility of Results; D012987:Soil / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D035501:Uncertainty
chemical_list: D012987:Soil