Effects of forest floor organic layer and root biomass on soil respiration following boreal forest fire

Soil respiration and its spatial and temporal variation were studied at three boreal forest sites in central Saskatchewan, Canada, burned in 1998, 1989, and 1977. Soil respiration, soil temperature, and organic layer thickness were measured at 100 points in a grid pattern of 2 m x 2 m at each site in 2004 and 2005. The mean within-site spatial coefficient of variation was 35%, and the measurements were not spatially autocorrelated. We found no significant difference in variance between the two youngest sites (P > 0.05), whereas the older site showed significantly lower variance (P < 0.05). Soil respiration was not correlated with the forest floor organic layer thickness at any of the sites (R-2 < 0.1). Removal of the forest floor layer reduced the soil respiration by 17% to 38%, depending on the site. Thus, the respiration from the mineral soil seemed to contribute a major fraction of the total soil respiration (62%-83%). Soil respiration was positively linearly related to the fine root biomass (R-2 = 0.63-0.85, P < 0.05) at all sites. We conclude that variation in root biomass has a larger effect than differential forest floor organic layers on variation in soil respiration in young boreal postfire forests.