title: Evaluating theories of drought-induced vegetation mortality using a multimodel-experiment framework.
abstract: Model-data comparisons of plant physiological processes provide an understanding of mechanisms underlying vegetation responses to climate. We simulated the physiology of a piñon pine-juniper woodland (Pinus edulis-Juniperus monosperma) that experienced mortality during a 5 yr precipitation-reduction experiment, allowing a framework with which to examine our knowledge of drought-induced tree mortality. We used six models designed for scales ranging from individual plants to a global level, all containing state-of-the-art representations of the internal hydraulic and carbohydrate dynamics of woody plants. Despite the large range of model structures, tuning, and parameterization employed, all simulations predicted hydraulic failure and carbon starvation processes co-occurring in dying trees of both species, with the time spent with severe hydraulic failure and carbon starvation, rather than absolute thresholds per se, being a better predictor of impending mortality. Model and empirical data suggest that limited carbon and water exchanges at stomatal, phloem, and below-ground interfaces were associated with mortality of both species. The model-data comparison suggests that the introduction of a mechanistic process into physiology-based models provides equal or improved predictive power over traditional process-model or empirical thresholds. Both biophysical and empirical modeling approaches are useful in understanding processes, particularly when the models fail, because they reveal mechanisms that are likely to underlie mortality. We suggest that for some ecosystems, integration of mechanistic pathogen models into current vegetation models, and evaluation against observations, could result in a breakthrough capability to simulate vegetation dynamics.
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Nate G
authors.initials: NG
authors.lastname: McDowell
authors.affiliation: Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, 80305, USA.
authors.forename: Rosie A
authors.initials: RA
authors.lastname: Fisher
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Chonggang
authors.initials: C
authors.lastname: Xu
authors.affiliation: University of Bordeaux, Bordeaux Sciences Agro, UMR INRA-TCEM 1220, 33140, Villenave d'Ornon, France.|Nicholas School of the Environment, Duke University, Box 90328, Durham, NC, 27708, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Domec
authors.affiliation: Department of Forest Sciences, University of Helsinki, PO Box 24, 00014, Helsinki, Finland.
authors.forename: Teemu
authors.initials: T
authors.lastname: Hölttä
authors.affiliation: Department of Geography, State University of New York at Buffalo, 105 Wilkeson Quadrangle, Buffalo, NY, 14261, USA.
authors.forename: D Scott
authors.initials: DS
authors.lastname: Mackay
authors.affiliation: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT, 84112, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Sperry
authors.affiliation: Department of Biology, MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131-0001, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Boutz
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Lee
authors.initials: L
authors.lastname: Dickman
authors.affiliation: Department of Biology, MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131-0001, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Gehres
authors.affiliation: Department of Biology, MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131-0001, USA.
authors.forename: Jean Marc
authors.initials: JM
authors.lastname: Limousin
authors.affiliation: School of Geography and Development and Laboratory of Tree-Ring Research, University of Arizona, 1215 Lowell Street, Tucson, AZ, 85721-0058, USA.
authors.forename: Alison
authors.initials: A
authors.lastname: Macalady
authors.affiliation: CREAF, Cerdanyola del Vallès, 08193, Spain.|Univ Autònoma Barcelona, Cerdanyola del Vallès, 08193, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Martínez-Vilalta
authors.affiliation: ICREA at CREAF, Cerdanyola del Vallès, 08193, Spain.|School of GeoSciences, University of Edinburgh Crew Building, West Mains Road, Edinburgh, EH9 3JN, UK.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Mencuccini
authors.affiliation: Department of Biology, MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131-0001, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Plaut
authors.affiliation: INRA, UR1263 EPHYSE, F-33140, Villenave d'Ornon, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Ogée
authors.affiliation: Department of Biology, MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131-0001, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Pangle
authors.affiliation: Bioforsk - Norwegian Institute for Agricultural and Environmental Research, Ås, Norway.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Rasse
authors.affiliation: Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523-1499, USA.|USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO, 80526, USA.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Ryan
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: Sanna
authors.initials: S
authors.lastname: Sevanto
authors.affiliation: College of Forestry, Oregon State University, Corvallis, OR, 97331-5704, USA.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Waring
authors.affiliation: Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: A Park
authors.initials: AP
authors.lastname: Williams
authors.affiliation: Departamento de Ciencias del Agua y del Medio Ambiente, Instituto Tecnológico de Sonora, Ciudad Obregón, Sonora, 85000, Mexico.
authors.forename: Enrico A
authors.initials: EA
authors.lastname: Yepez
authors.affiliation: Department of Biology, MSC03 2020, 1 University of New Mexico, Albuquerque, NM, 87131-0001, USA.
authors.forename: William T
authors.initials: WT
authors.lastname: Pockman
mesh_terms: D002244:Carbon / Q000378:metabolism*; D055864:Droughts; D018653:Juniperus / Q000254:growth & development / Q000502:physiology*; D008954:Models, Biological; D052585:Phloem / Q000254:growth & development / Q000502:physiology; D028223:Pinus / Q000254:growth & development / Q000502:physiology*; D054046:Plant Stomata / Q000254:growth & development / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D011891:Rain; D013312:Stress, Physiological; D013696:Temperature; D014197:Trees; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water; D002244:Carbon
keywords: carbon starvation; cavitation; die-off; dynamic global vegetation models (DGVMs); hydraulic failure; photosynthesis; process-based models