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Published July 16, 2005 | Supplemental Material + Published
Journal Article Open

Changes in the surface energy budget after fire in boreal ecosystems of interior Alaska: An annual perspective


Understanding links between the disturbance regime and regional climate in boreal regions requires observations of the surface energy budget from ecosystems in various stages of secondary succession. While several studies have characterized fire‐induced differences in surface energy fluxes from boreal ecosystems during summer months, much less is known about these differences over the full annual cycle. Here we measured components of the surface energy budget (including both radiative and turbulent fluxes) at three sites from a fire chronosequence in interior Alaska for a 1‐year period. Our sites consisted of large burn scars resulting from fires in 1999, 1987, and ∼1920 (hereinafter referred to as the 3‐, 15‐, and 80‐year sites, respectively). Vegetation cover consisted primarily of bunch grasses at the 3‐year site, aspen and willow at the 15‐year site, and black spruce at the 80‐year site. Annual net radiation declined by 31% (17 W m^(−2)) for both the 3‐ and the 15‐year sites as compared with the 80‐year site (which had an annual mean of 55 W m^(−2)). Annual sensible heat fluxes were reduced by an even greater amount, by 55% at the 3‐year site and by 52% at the 15‐year site as compared with the 80‐year site (which had an annual mean of 21 W m^(−2)). Absolute differences between the postfire ecosystems and the mature black spruce forest for both net radiation and sensible heat fluxes were greatest during spring (because of differences in snow cover and surface albedo), substantial during summer and winter, and relatively small during fall. Fire‐induced disturbance also initially reduced annual evapotranspiration (ET). Annual ET decreased by 33% (99 mm yr^(−1)) at the 3‐year site as compared with the 80‐year site (which had an annual flux of 301 mm yr^(−1)). Annual ET at the 15‐year site (283 mm yr^(−1)) was approximately the same as that from the 80‐year site, even though the 15‐year site had substantially higher ET during July. Our study suggests that differences in annual ET between deciduous and conifer stands may be smaller than that inferred solely from summer observations. This study provides a direct means to validate land surface processes in global climate models attempting to capture vegetation‐climate feedbacks in northern terrestrial regions.

Additional Information

© 2005 by the American Geophysical Union. Received 23 June 2004; revised 28 January 2005; accepted 25 February 2005; published 1 July 2005. We thank M. Mack, E. A. G. Schuur, K. Treseder, and J. Harden for providing data on vegetation and soils at these sites and S. D. Chambers for providing invaluable insight about eddy covariance measurement techniques in boreal ecosystems. C. Dunn, J. Henkelman, and J. Smith contributed substantially to the development of these sites. J. Garron provided invaluable technical assistance throughout the year of this study. We are grateful for constructive suggestions and comments from three anonymous reviewers. This work was supported by an NSF RAISE grant OPP‐0097439, the Powell Foundation, and a gift from the Davidows to Caltech.

Attached Files

Published - Liu_et_al-2005-Journal_of_Geophysical_Research_3A_Atmospheres__281984-2012_29.pdf

Supplemental Material - downloadSupplement_doi=10.1029_2F2004JD005158_file=jgrd11688-sup-0001-t01.txt

Supplemental Material - downloadSupplement_doi=10.1029_2F2004JD005158_file=jgrd11688-sup-0002-t02.txt

Supplemental Material - downloadSupplement_doi=10.1029_2F2004JD005158_file=jgrd11688-sup-0003-t03.txt

Supplemental Material - downloadSupplement_doi=10.1029_2F2004JD005158_file=jgrd11688-sup-0004-t04.txt



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