Recovery of forest-floor vegetation after a wildfire in a Picea mariana forest

We aimed to detect the trajectories of forest-floor vegetation recovery in a Picea mariana forest after a wildfire. Since fire severity in boreal forests is expected to increase because of climate changes, we investigated the effects of ground-surface burn severity, a surrogate for overall fire severity, on the revegetation. We annually monitored vegetation <1.3 m high in 80 1 m × 1 m quadrats at Poker Flat Research Range (65°12′N, 147°46′W, 650 m a.s.l.) near Fairbanks, interior Alaska, where a large wildfire occurred in the summer of 2004, from 2005 to 2009. Sphagnum mosses were predominant on the unburned ground surface. In total, 66 % of the ground surface was burned completely by the wildfire. Total plant cover increased from 48 % in 2005 to 83 % in 2009. The increase was derived mostly by the vegetative reproduction of shrubs on the unburned surface and by the immigration of non-Sphagnum mosses and deciduous trees on the burned surface. Deciduous trees, which had not been established before the wildfire, colonized only on the burned surface and grew faster than P. mariana. Although species richness decreased with increasing slope gradient, these deciduous trees became established even on steep slopes. The wildfire that completely burned the ground surface distorted the revegetation, particularly on steep slopes. The restoration of the Sphagnum surface was a prerequisite after the severe wildfire occurred, although the Sphagnum cover had difficulty returning to predominance in the short term.