Introduction

Boreal peatlands of Western Canada

Boreal peatland ecosystems occupy less than 3% of the earth's land surface, yet store between 250 and 455 Pg of C, which is roughly 20%–30% of the world's soil carbon (Gorham 1991; Charman 2002; Joosten & Clarke 2002; Vasander & Kettunen 2006). In continental western Canada, peatlands cover 365,157 km2 (Vitt et al. 2000) and dominate the landscape in northern Alberta, Saskatchewan, and Manitoba (Tarnocai 1984, 1998; Vitt et al. 2000; Tarnocai et al. 2005). Overall, these western Canadian peatlands have sequestered about 48 Pg of C during the past 10,000 years, with about half of this peat accumulated in the past 4000 years (Vitt et al. 2000). Peatlands provide a wide diversity of ecosystem services, not the least of which is the conversion of atmospheric CO2 into large accumulations of stored organic carbon (C) – a testament to the long-term function of these ecosystems as net C sinks since their widespread initiation after the most recent glacial retreat (Halsey et al. 2000). Bryophytes typically are dominant components of the vegetation in northern peatlands and play central roles with regard to nutrient cycling and carbon accumulation.

The initiation, development, succession, and rate of peat accumulation in boreal peatlands are dependent on regional factors such as climate, substrate chemistry, landscape position, and hydrological regime.

Introduction

Peatlands are unbalanced ecosystems where plant production exceeds decomposition of organic material. As a result, considerable quantities of organic material, or peat, accumulate over long periods of time: millennia. This organic material is composed primarily of plant fragments remaining after partial decomposition of the plants that at one time lived on the surface of the peatland. Decomposition occurs through the action of micro-organisms that have the ability to utilize dead plant components as sources of carbon for respiration (Thormann & Bayley 1997) in both the upper, aerobic peat column (the acrotelm) and the lower, anaerobic peat (the catotelm) (Ingram 1978, Clymo 1984, Wieder et al. 1990, Kuhry & Vitt 1996). Labile cell contents, cellulose, and hemicellulose are more readily available sources of carbon than recalcitrant fractions that contain lignin-like compounds, with these latter compounds being concentrated in peat by decomposition (Williams et al. 1998, Turetsky et al. 2000). The vascular plant-dominated, tree, shrub, and herb layers produce less biomass (Campbell et al. 2000) and decompose more readily than the bryophyte-dominated ground layer (Moore 1989). Surfaces of northern peatlands are almost always completely covered by a continuous mat of moss (National Wetlands Working Group 1988, Vitt 1990), and the large amount of biomass contained in this layer is composed of cell wall material that decomposes slowly. This slow decomposition, coupled with water-saturated, anaerobic conditions in the peat, cool climate, and a cool moist growing season conducive to bryophyte growth, allows organic matter to accumulate over large areas.