Methane and carbon dioxide exchanges between the atmosphere and northern boreal forest soils

CH 4 and CO 2 fluxes were measured in upland boreal forest soils near Thompson, Manitoba, from May 16 to September 16, 1994. Most sites consumed atmospheric CH 4 , fluxes ranging from +0.6 to −2.6 mg CH 4 m −2 d −1 , and emitted CO 2 at rates between 0.2 and 26.8 g CO 2 m −2 d −1 . There was some evidence of episodic CH 4 emissions after heavy rainfall from soils which normally consumed CH 4 . There were two distinct groups: sites in which both CO 2 and CH 4 exchange was strong (mean 5.2 g CO 2 m −2 d −1 , −1.0 mg CH 4 m −2 d −1 ); and those which had a weak exchange of both gases (mean 2.5 g CO 2 m −2 d −1 , −0.2 mg CH 4 m −2 d −1 ). The presence of black spruce trees, a Sphagnum spp. ground cover and a thick organic layer (20–50 cm) characterized the weak exchange group. These characteristics were indicative of colder, wetter conditions with slower N cycling and longer path lengths to the zone of CH 4 oxidation. The strong exchange group had either aspen, jack pine, or birch trees; a vascular plant cover; and a thin organic layer (1–5 cm). These characteristics were indicative of warmer, drier conditions with faster N cycling and shorter path lengths to the zone of CH 4 oxidation. The seasonal average of both CO 2 and CH 4 flux from 11 sites could be predicted by regressions involving the amount of soil organic matter (0–5 cm depth) and seasonal temperature at a depth of 20 cm ( r 2 =0.69 and 0.82, respectively). Using these vegetation characteristics and a Landsat image of the Boreal Ecosystem‐Atmosphere Study (BOREAS) northern study area for areal weighting, net gas fluxes were calculated for the upland soils, estimated to be −0.4 mg CH 4 m −2 d −1 and 4 g CO 2 m −2 d −1 .