Linking microtopography with post‐fire succession in bogs

Questions: Does post‐fire plant succession in boreal bogs vary microtopographically and are successional patterns reproducible among similar microtopographic features? Does succession preserve microtopography post‐fire? Location: Boreal bog peatlands near Sinkhole Lake and Athabasca, Alberta, Canada. Methods: We assessed microtopographic variation in post‐fire plant community succession through stratigraphic macrofossil analysis of bog soil cores collected from high (hummock) and low (hollow) positions. We conducted vegetation surveys and collected soil cores from ten hummocks and hollows in each bog. Pre‐fire microtopographic status was inferred based on floral composition and compared to current microtopography. Results: Hollow vegetation was more variable than hummocks, both in present composition and post‐fire succession. The successional trajectory of current hummocks was relatively uniform, showing relatively rapid shifts to Sphagnum fuscum dominance, but varied greatly in hollows. Hollows, although compositionally variable, were typically perpetuated following fire, while hummocks had an approximately equal chance of being perpetuated or becoming hollows. Conclusions: Greater compositional variability at lower microtopographic positions, both spatially and temporally, is most likely due to the ability of hollows to support a wider range of species and greater susceptibility to severe disturbance. Likewise, spatial variability in fire severity appears to be responsible for perpetuation or change in microtopographic status, favouring the creation of hollows over maintenance of hummocks.