title: Emergent climate and CO2sensitivities of net primary productivity in ecosystem models do not agree with empirical data in temperate forests of eastern North America.
abstract: Ecosystem models show divergent responses of the terrestrial carbon cycle to global change over the next century. Individual model evaluation and multimodel comparisons with data have largely focused on individual processes at subannual to decadal scales. Thus far, data-based evaluations of emergent ecosystem responses to climate and CO2at multidecadal and centennial timescales have been rare. We compared the sensitivity of net primary productivity (NPP) to temperature, precipitation, and CO2in ten ecosystem models with the sensitivities found in tree-ring reconstructions of NPP and raw ring-width series at six temperate forest sites. These model-data comparisons were evaluated at three temporal extents to determine whether the rapid, directional changes in temperature and CO2in the recent past skew our observed responses to multiple drivers of change. All models tested here were more sensitive to low growing season precipitation than tree-ring NPP and ring widths in the past 30 years, although some model precipitation responses were more consistent with tree rings when evaluated over a full century. Similarly, all models had negative or no response to warm-growing season temperatures, while tree-ring data showed consistently positive effects of temperature. Although precipitation responses were least consistent among models, differences among models to CO2drive divergence and ensemble uncertainty in relative change in NPP over the past century. Changes in forest composition within models had no effect on climate or CO2sensitivity. Fire in model simulations reduced model sensitivity to climate and CO2, but only over the course of multiple centuries. Formal evaluation of emergent model behavior at multidecadal and multicentennial timescales is essential to reconciling model projections with observed ecosystem responses to past climate change. Future evaluation should focus on improved representation of disturbance and biomass change as well as the feedbacks with moisture balance and CO2in individual models.
authors.affiliation: Department of Earth & Environment, Boston University, 685 Commonwealth Ave, Boston, MA, 02215, USA.|Morton Arboretum, 4100 Illinois Route 53, Lisle, IL, 60532, USA.
authors.forename: Christine R
authors.identifier: 0000-0003-0181-7293
authors.initials: CR
authors.lastname: Rollinson
authors.affiliation: School of Natural Resources, University of Arizona, 1064 E. Lowell St., Tucson, AZ, 85721, USA.
authors.forename: Yao
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Biological Sciences, University of Notre Dame, 176 Galvin Life Science Center, Notre Dame, IN, 46556, USA.
authors.forename: Ann
authors.initials: A
authors.lastname: Raiho
authors.affiliation: School of Natural Resources, University of Arizona, 1064 E. Lowell St., Tucson, AZ, 85721, USA.
authors.forename: David J P
authors.initials: DJP
authors.lastname: Moore
authors.affiliation: Department of Biological Sciences, University of Notre Dame, 176 Galvin Life Science Center, Notre Dame, IN, 46556, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: McLachlan
authors.affiliation: Havard Forest, 324 N. Main St, Petersham, MA, 10366, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Bishop
authors.affiliation: Department of Geology and Geography, West Virginia University, P.O. Box 6300, Morgantown, WV, 26506, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Dye
authors.affiliation: Department of Biological Sciences, Wellesley College, 106 Central Street, Wellesley, MA, 02481, USA.
authors.forename: Jaclyn H
authors.initials: JH
authors.lastname: Matthes
authors.affiliation: Department of Geology and Geography, West Virginia University, P.O. Box 6300, Morgantown, WV, 26506, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Hessl
authors.affiliation: Senkenberg Biodiversity and Climate Research Centre (BiK-F), Senkenberganlage 25, Frankfurt am Main, D-60325, Germany.|Department of Physical Geography and Geosciences, Goethe University, Altenhöferallee 1, Frankfurt am Main, 60438, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hickler
authors.affiliation: Havard Forest, 324 N. Main St, Petersham, MA, 10366, USA.
authors.forename: Neil
authors.initials: N
authors.lastname: Pederson
authors.affiliation: Biospheric Science Laboratory, NASA Goodard Space Flight Center, Greenbelt, MD, 22071, USA.|Institute on Ecosystem and Department of Ecology, Montana State University, Bozeman, MT, 59717, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Poulter
authors.affiliation: Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading, RG6 6BB, UK.
authors.forename: Tristan
authors.initials: T
authors.lastname: Quaife
authors.affiliation: National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, 449 UCB, Boulder, CO, 80309, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Schaefer
authors.affiliation: Senkenberg Biodiversity and Climate Research Centre (BiK-F), Senkenberganlage 25, Frankfurt am Main, D-60325, Germany.
authors.forename: Jörg
authors.identifier: 0000-0002-7861-8789
authors.initials: J
authors.lastname: Steinkamp
authors.affiliation: Department of Earth & Environment, Boston University, 685 Commonwealth Ave, Boston, MA, 02215, USA.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Dietze
mesh_terms: D002245:Carbon Dioxide; D002980:Climate; D057231:Climate Change; D017753:Ecosystem; D065928:Forests; D009656:North America; D014197:Trees
chemical_list: D002245:Carbon Dioxide
keywords: climate change; climate sensitivity; ecosystem model; emergent response; model-data comparison; net primary productivity; paleoecology; tree rings