Postfire carbon balance in boreal bogs of Alberta, Canada

• Published in: Global change biology 2009, Vol.15 (1), p.63-81
• Main Authors: WIEDER, R. KELMAN, SCOTT, KIMBERLI D, KAMMINGA, KATHERINE, VILE, MELANIE A, VITT, DALE H, BONE, TIFFANY, XU, BIN, BENSCOTER, BRIAN W, BHATTI, JAGTAR S
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; black spruce; bog; boreal; Canada; Carbon; carbon cycling; Climate change; Climatology. Bioclimatology. Climate change; Earth, ocean, space; Exact sciences and technology; External geophysics; fire; fires; Forest & brush fires; Fundamental and applied biological sciences. Psychology; General aspects; Human influences; Meteorology; peatland; Picea mariana; roots; Sphagnum; Wetlands
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/j.1365-2486.2008.01756.x

Boreal peatland ecosystems occupy about 3.5 million km² of the earth's land surface and store between 250 and 455 Pg of carbon (C) as peat. While northern hemisphere boreal peatlands have functioned as net sinks for atmospheric C since the most recent deglaciation, natural and anthropogenic disturbances, and most importantly wildfire, may compromise peatland C sinks. To examine the effects of fire on local and regional C sink strength, we focused on a 12 000 km² region near Wabasca, AB, Canada, where ombrotrophic Sphagnum-dominated bogs cover 2280 km² that burn with a fire return interval of 123±26 years. We characterized annual C accumulation along a chronosequence of 10 bog sites, spanning 1-102 years-since-fire (in 2002). Immediately after fire, bogs represent a net C source of 8.9±8.4 mol m⁻² yr⁻¹. At about 13 years after fire, bogs switch from net C sources to net C sinks, mainly because of recovery of the moss and shrub layers. Subsequently, black spruce biomass accumulation contributes to the net C sink, with fine root biomass accumulation peaking at 34 years after fire and aboveground biomass and coarse root accumulation peaking at 74 years after fire. The overall C sink strength peaks at 18.4 mol C m⁻² yr⁻¹ at 75 years after fire. As the tree biomass accumulation rate declines, the net C sink decreases to about 10 mol C m⁻² yr⁻¹ at 100 years-since-fire. We estimate that across the Wabasca study region, bogs currently represent a C sink of 14.7±5.1 Gmol yr⁻¹. A decrease in the fire return interval to 61 years with no change in air temperature would convert the region's bogs to a net C source. An increase in nonwinter air temperature of 2 °C would decrease the regional C sink to 6.8±2.3 Gmol yr⁻¹. Under scenarios of predicted climate change, the current C sink status of Alberta bogs is likely to diminish to the point where these peatlands become net sources of atmospheric CO₂-C.