Comparison of net ecosystem production at mature and disturbed forest sites, Saskatchewan, Canada 2001–02

Fire and harvesting are important disturbances in the boreal forest, driving net biome production. Measurements of net ecosystem production (NEP) over mature forest stands have been made from flux towers for about a decade at the Boreal Ecosystem Research and Monitoring Sites (BERMS) in central Saskatchewan, Canada. Over the last few years, the network of towers has been expanded to include stands that were recently disturbed by fire or harvesting. These new towers are part of Fluxnet-Canada, a national network that ties into the international Fluxnet network. Data from 2001 and 2002 show that forests burned in 1998 or harvested in 1994 are net carbon sources to the atmosphere with annual NEP values in the range of -50 to -100 g C m^-2 y^-1. A site burned in 1989 is a carbon sink of about 60 g C m^-2 y^-1, whereas NEP at a mature jack pine or black spruce stand ranged from carbon neutral to about 70 g C m^-2 y^-1. A mature aspen site had the greatest NEP with 360 g C m^-2 y^-1 in 2001 and 140 g C m^-2 y^-1 in 2002, the decrease likely caused by a long-term drought at the site. These data indicate that there is still a broad gap in our knowledge of carbon fluxes to forest stands between about 10 and 50 years of age. This is especially important in view of predictions of more boreal fire disturbance in the future.