Fire effects on net radiation and energy partitioning: Contrasting responses of tundra and boreal forest ecosystems

S D Chambers,J Beringer,F S Chapin,J T Randerson

doi:10.1029/2004jd005299

Abstract

The net radiation available to drive surface‐atmosphere exchange is strongly influenced by albedo and surface temperature. Tower‐based microclimatic and eddy covariance measurements in typical Alaskan black spruce and tundra ecosystems before and immediately after fire indicated a 10% decrease in net radiation over the burned spruce stand but a 12% increase in net radiation over the burned tundra surface. In both cases, there was increased partitioning of net radiation into sensible heat flux. In terms of absolute fluxes, however, fire increased average sensible heating over tundra by ∼50 W m−2 but caused little change in average sensible heat flux over the black spruce forest. This difference in fire effects occurred because fire altered the canopy characteristics (including surface roughness) more strongly in the forest than in the tundra, leading to a greater reduction in surface‐atmosphere coupling over the forest.

Highlights

The similarities in response to fire observed between mean and clear-sky conditions indicate that the changes in radiation efficiency of each stand were primarily caused by fireinduced changes in albedo and surface temperature rather than atmospheric conditions
[28] The most striking result of our study is the dramatic effects of canopy simplification on the postfire energy budget
In the tundra, where fire had only small effects on canopy architecture, surface temperature, or longwave emission, the effects of surface charring dominated over effects of canopy coupling with the atmosphere, causing an increase in net radiation

Summary

Introduction

[2] Fire plays an important role in the functioning and spatial heterogeneity of boreal forests. Under current climatic conditions, $3 million hectares of North American boreal forest burn annually [Kasischke et al, 1995]. This rate has doubled in western North America in the last 40 years and has been linked to high-latitude warming [Murphy et al, 2000]. Measurements by Rouse [1976] examined the radiation balance but neglected the surface energy budget. A more comprehensive suite of airborne measurements were made over some Canadian boreal forest stands in early postfire succession by Amiro et al [1999], they are limited in temporal

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Discussion

Conclusions