Association of postfire peat accumulation and microtopography in boreal bogs

Abstract

Peatlands accumulate organic matter as peat because of disproportionate rates of production and decomposition. However, peat accumulation heterogeneity has not been well studied along the microtopographic gradient (hummocks vs. hollows), particularly with respect to fire. Fire affects peatland species composition by differentially removing vegetation and resetting succession, resulting in peat accumulation changes. We examined peat accumulation and microtopography in two historically burned bogs in Alberta, Canada. Measurements of current and historic microtopography were made, and cores were collected along the gradient to identify depth of peat accumulated since fire, as well as to assess properties of the accumulated peat. Current microtopography is significant and correlated with the immediate postfire surface relief. However, differences in the magnitude of variability between sites suggests that differential rates of growth between features are exacerbated between sites and reflected in bog microtopography. Rates of organic matter accumulation, ranging from 156 to 257 g·m–2·year–1, were elevated but comparable to published rates of recent accumulation. Organic matter content and accumulation rate were greater for hummocks than hollows at Athabasca bog, but the difference between features diminished at Sinkhole Lake, suggesting that the pattern and properties of peat accumulation and microtopography postfire may be attributable to differences in site conditions.