title: No growth stimulation of Canada's boreal forest under half-century of combined warming and CO2 fertilization.
abstract: Considerable evidence exists that current global temperatures are higher than at any time during the past millennium. However, the long-term impacts of rising temperatures and associated shifts in the hydrological cycle on the productivity of ecosystems remain poorly understood for mid to high northern latitudes. Here, we quantify species-specific spatiotemporal variability in terrestrial aboveground biomass stem growth across Canada's boreal forests from 1950 to the present. We use 873 newly developed tree-ring chronologies from Canada's National Forest Inventory, representing an unprecedented degree of sampling standardization for a large-scale dendrochronological study. We find significant regional- and species-related trends in growth, but the positive and negative trends compensate each other to yield no strong overall trend in forest growth when averaged across the Canadian boreal forest. The spatial patterns of growth trends identified in our analysis were to some extent coherent with trends estimated by remote sensing, but there are wide areas where remote-sensing information did not match the forest growth trends. Quantifications of tree growth variability as a function of climate factors and atmospheric CO2concentration reveal strong negative temperature and positive moisture controls on spatial patterns of tree growth rates, emphasizing the ecological sensitivity to regime shifts in the hydrological cycle. An enhanced dependence of forest growth on soil moisture during the late-20th century coincides with a rapid rise in summer temperatures and occurs despite potential compensating effects from increased atmospheric CO2concentration.
authors.affiliation: Laurentian Forestry Centre, Canadian Forest Service, Natural Resources Canada, Quebec, QC, Canada G1V 4C7; martin.girardin@canada.ca.
authors.forename: Martin P
authors.initials: MP
authors.lastname: Girardin
authors.affiliation: Northern Forestry Centre, Canadian Forest Service, Natural Resources Canada, Edmonton, AB, Canada T6H 3S5.
authors.forename: Olivier
authors.identifier: 0000-0002-8046-466X
authors.initials: O
authors.lastname: Bouriaud
authors.affiliation: Northern Forestry Centre, Canadian Forest Service, Natural Resources Canada, Edmonton, AB, Canada T6H 3S5.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Hogg
authors.affiliation: Pacific Forestry Centre, Canadian Forest Service, Natural Resources Canada, Victoria, BC, Canada V8Z 1M5.
authors.forename: Werner
authors.initials: W
authors.lastname: Kurz
authors.affiliation: Landscape Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland.|Department of Environmental Systems Sciences, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland.
authors.forename: Niklaus E
authors.initials: NE
authors.lastname: Zimmermann
authors.affiliation: Northern Forestry Centre, Canadian Forest Service, Natural Resources Canada, Edmonton, AB, Canada T6H 3S5.
authors.forename: Juha M
authors.initials: JM
authors.lastname: Metsaranta
authors.affiliation: Remote Sensing Laboratories, University of Zurich, CH-8057 Zurich, Switzerland.
authors.forename: Rogier
authors.initials: R
authors.lastname: de Jong
authors.affiliation: Landscape Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland.|Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721.
authors.forename: David C
authors.initials: DC
authors.lastname: Frank
authors.affiliation: Department of Geography, Johannes Gutenberg University, 55099 Mainz, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Esper
authors.affiliation: Landscape Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research, CH-8903 Birmensdorf, Switzerland.|Oeschger Centre for Climate Change Research, 3012 Bern, Switzerland.
authors.forename: Ulf
authors.initials: U
authors.lastname: Büntgen
authors.affiliation: Laurentian Forestry Centre, Canadian Forest Service, Natural Resources Canada, Quebec, QC, Canada G1V 4C7.
authors.forename: Xiao Jing
authors.initials: XJ
authors.lastname: Guo
authors.affiliation: Northern Forestry Centre, Canadian Forest Service, Natural Resources Canada, Edmonton, AB, Canada T6H 3S5.
authors.forename: Jagtar
authors.initials: J
authors.lastname: Bhatti
mesh_terms: D018533:Biomass; D002170:Canada; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000737:chemistry*; D057231:Climate Change; D004463:Ecology; D065928:Forests; D005843:Geography; D015233:Models, Statistical; D012044:Regression Analysis; D066188:Taiga; D013696:Temperature; D013997:Time Factors; D014197:Trees / Q000254:growth & development*
chemical_list: D002245:Carbon Dioxide
keywords: climate change; dendrochronology; drought impacts; ecology; normalized difference vegetation index