Climatic and Phenological Controls of the Carbon and Energy Balances of Three Contrasting Boreal Forest Ecosystems in Western Canada

  • Alan Barr
  • T. Andrew Black
  • Harry McCaughey


Seasonal and interannual variability in the carbon and energy cycles of boreal forests are controlled by the interaction of climate, ecophysiology and plant phenology. This study analyses eddy-covariance data from mature trembling aspen, black spruce and jack pine stands in western Canada. The seasonal cycles of the surface carbon and energy balances were tightly coupled to the seasonal cycle of soil temperature. The contiguous carbon-uptake period was ∼50 days longer for the black spruce and jack pine stands than the trembling aspen stand, with 30 days difference in spring and 20 days difference in autumn. The black spruce and jack pine carbon-uptake period spanned the warm season, with gross ecosystem photosynthesis beginning during spring thaw and continuing until air temperature dropped to below freezing in autumn. In contrast, the trembling aspen carbon-uptake period was determined by the timing of leaf emergence and senescence, which occurred well after spring thaw and before autumn freeze. Regression analysis identified spring temperature as the primary factor controlling annual net ecosystem production at all three sites, through its influence on the onset of the growing season. Precipitation and soil water content had significant but secondary influences on the annual carbon fluxes. The impact of spring warming on annual net ecosystem production was 2–3 times greater at the deciduous-broadleaf than the evergreen-coniferous sites, confirming the high sensitivity of boreal deciduous-broadleaf forests to spring warming. The analysis confirmed the pivotal role of phenology in the response of northern ecosystems to climate variability and change.


Normalize Difference Vegetation Index Boreal Forest Leaf Area Index Grow Season Spring Temperature 
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absorbed photosynthetically-active radiation (mol m 2 y 1) (Eqn. 8a, 8b)


carbon-uptake period (days)


day of year


end date of growing season (Table 2)


evaporative fraction (Eqn. 3)


net ecosystem production (μmol m−2 s−1) or (g C m−2 y−1)


gross ecosystem photosynthesis (μmol m−2 s−1) or (g C m−2 y−1)


ecosystem respiration (μmol m−2 s−1) or (g C m−2 y−1)


growing season


sensible heat flux density (W m−2)


leaf area index


length of growing season (days, Table 2)


broadband estimate of the normalized difference vegetation index (Eqn. 7)


onset date of growing season (Table 2)


annual total precipitation (mm)


total precipitation from current and previous years (mm)


photosynthetically-active radiation


sum of surface storage energy flux densities (W m−2)


net radiation flux density (W m−2)


global incoming shortwave flux density (W m−2)


soil volumetric water content


air temperature above the forest canopy (°C)


soil temperature at 5, 10 or 20-cm depth from the top of the surface organic horizon (°C)


Bowen ratio (Eqn. 4)


cumulative degree days (°C days, Eqn. 5)


latent heat flux density (W m 2)



We gratefully acknowledge the contributions of Charmaine Hrynkiw, Dell Bayne, Erin Thompson, Joe Eley, Alison Theede, Bruce Cole, Craig Smith and Steve Enns, who oversaw the meteorological measurements and data management; Zoran Nesic, Andrew Sauter, Rick Ketler, Dominic Lessard, Dan Finch and Sheila McQueen, who provided laboratory, field and data management support for the flux measurements; and Barry Goodison and Bob Stewart, who championed the BERMS program. Financial support was provided by the Climate Research Division of Environment Canada, the Canadian Forest Service, Parks Canada, the Action Plan 2000 on Climate Change, the Program of Energy Research and Development, the Climate Change Action Fund, the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Climate and Atmospheric Sciences, the BIOCAP Canada Foundation, and the National Aeronautic and Space Administration.


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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.Climate Research DivisionEnvironment CanadaSaskatoonCanada
  2. 2.Faculty of Land and Food SystemsUniversity of British ColumbiaVancouverCanada
  3. 3.Department of GeographyQueen’s UniversityKingstonCanada

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