Ecological factors shaping postfire resilience in mature black spruce forests of eastern North America

This dataset encompasses 536 entries, each representing a 400 m² stand of post-fire regeneration of black spruce (Picea mariana) in the eastern North American boreal zone, affected by 21 fires that occurred between 1995 and 2016. It focuses on the post-fire recovery and resilience of mature stand of black spruce (Picea mariana), a species adapted to stand-replacing fires. The dataset includes unique identifiers, geographical locations, fire characteristics, and metrics for both pre-fire and post-fire vegetation, particularly post-fire seedling density (seedlings/ha).

The dataset allows for exploring key ecological determinants of post-fire regeneration, including seed bank conditions, fire severity, and seedbed condition. This comprehensive network facilitates an unprecedented spatial and temporal analysis of black spruce regeneration. Legal and ethical considerations involve ensuring proper data handling.

Research utilizing this dataset can inform forest management strategies and ecological assessments, underscoring the potential shifts, principally toward loss of black-spruce density, in boreal forest dynamics under climate-induced fire regime changes.

Methods
The studied fires were selected because: (i) they were located within the boreal closed crown forest in the province of Quebec; (ii) they were composed of mature (60 years) BS-dominated pre-fire stands (>50% of the basal area occupied by BS); (iii) they had burned a minimum of three years before field surveys to allow time for post-fire seedling establishment; (iv) they had burned after 1984 (v) they had not been salvage logged; and (vi) they were accessible by road. Across all selected fires, 536 circular plots of 400 m² (r = 11.28 m) were sampled during the summers of 2017, 2018, 2019, and 2020 following a systematic sampling design, with at least three plots distributed along the lower, middle, and upper portions of each slope and spaced at least 100 meters apart. Depending on the fire size and accessibility, between 4 and 152 plots were established by fire. The percentage cover of each understory plant species in each plot was assessed using the point-intercept method. This involved two perpendicular transect lines, each measuring 22.56 m, resulting in a total length of 45.12 m across the plot. At every 0.5 m increment along these lines,1.5-metre-long metal rods were placed perpendicularly. The number of rods that were touched by eachspecies across a plot was counted and divided by the total number of rods, yielding a percent cover value. The percentage ground cover of understory plants was obtained, including living Sphagnum spp. moss and ericaceous shrubs. All living post-fire tree seedlings (height > 0.01 m) of each of the main tree species, which included BS, JP, paper birch or trembling aspen (forming 99.9% of all tree stems), were counted in 10 evenly distributed 4m2 subplots. Within-plot, stocking was also calculated as the percentage of subplots occupied by at least one seedling. The thickness (cm) of the post-fire residual organic layer was measured at the center of each of the 10 subplots.