Year: 2007
Abstract:
Peatland ecosystems, which are predominantly found in northern boreal regions of Canada and Russia, accumulate carbon because photosynthetic production of the mosses dominating the ground layer exceeds their decomposition, thereby generating peat. Production and decomposition rates, and therefore peat accumulation, are species-specific. Therefore, changes in ground layer composition will have an effect on boreal peatland function.Fire is the most prevalent disturbance for boreal, western Canadian peatlands. Ombrotrophic, forested bogs are most affected by fire due to a drier peat surface relative to other peatland landforms and an extensive Picea mariana canopy. In addition to direct C losses during peat combustion, fire has indirect effects on bog C cycling through removal of the ground layer vegetation and alteration of the surface environment. Because peat accumulation varies among species, functional recovery post-fire is linked to ground layer succession, which varies with combustion severityTo assess the post-fire compositional and functional recovery trajectories of western Canadian bogs, I monitored the ground layer community structure, production, and decomposition from 2003 to 2006 along a chronosequence of historically burned bogs (1-106 years since fire). Ground layer succession was tri-phasic, grading from pioneer true mosses early post-fire (1-10 ysf) to a Sphagnum -dominated community (20-80 ysf), followed by feathermoss encroachment at the longest recovery times (>90 ysf). However, the ground layer biomass production trajectory was asymptotic, stabilizing at ca. 20 years post-fire and coinciding with Sphagnum dominance of the ground layer community. Decomposition in the upper peat column (top 40-cm) did not vary along the chronosequence.From my results, I developed models to assess the impact of an altered fire regime on peatland C storage. Increases in annual extent of wildfire and combustion severity under a 2xCO 2 scenario substantially extend the peatland C pool recovery time. Furthermore, other models suggest a substantial reduction of the fire return interval (< 70 yrs) will cause peatlands to become sources, rather than sinks, of atmospheric C. Warming will enhance this effect, requiring less of a reduction in fire interval to trigger the functional switch from carbon sink to source.
