Spatial Patterns and Temporal Trajectories of the Bog Ground Layer Along a Post-Fire Chronosequence

Peatland ground layer species composition is intricately tied to ecosystem function (for example, carbon storage). As the primary disturbance in boreal bogs, wildfire selectively removes the ground layer vegetation, creating heterogeneous habitat conditions and initiating succession. However, the successional trajectory of the ground layer community following fire is poorly understood. Here we assess spatial and temporal changes in community composition along a chronosequence of post-fire bogs (1-105 years since fire) in north central Alberta, Canada. We established vegetation plots in 13 bogs and repeatedly monitored them from 2003-2006. We found three phases of the post-fire bog community, grading from pioneer true moss (for example, Polytrichum strictum) dominance soon post-fire (< 10 ysf) to persistent Sphagnum dominance in mature sites (20-80 ysf) with partial replacement by feathermosses (for example, Pleurozium schreberi) in older bogs (> 80 ysf). Mature bogs dominated by Sphagnum fuscum had the greatest species richness, although species evenness was low. Spatial heterogeneity of ground layer community composition was bimodal, peaking approximately 10 ysf (co-occurrence of true mosses and Sphagnum) and more than 80 ysf when feathermosses encroach and break-up Sphagnum dominance, resulting in inverse relationships of community species richness and diversity along the post-fire recovery gradient. Based on these results, we develop a conceptual model of post-fire bog recolonization and succession, in which microtopography, soil moisture, and combustion severity interact, thereby presenting the first comprehensive description of the spatio-temporal post-fire successional trajectory of the bog ground layer.