Beyond black spruce: shift in plant communities after frequent fire in a Yukon subarctic boreal forest

Wasyliw, Carissa (2023) Beyond black spruce: shift in plant communities after frequent fire in a Yukon subarctic boreal forest. Masters thesis, Memorial University of Newfoundland.

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Abstract

Rapid warming in northern climates is altering plant successional trajectories at their northern extent. Changing fire regimes under ongoing climate change are predicted to further influence shifts in vegetation successional trajectories in boreal forests. New fire regimes impact ecosystem vegetation legacies, which dictate the regeneration success of forests and can rapidly change ecosystem states to non-forested trajectories. Two closely timed fires (1990/1, 2005) in the Eagle Plains region of northern Yukon resulted in a failure of black spruce (Picea mariana) regeneration. Our study characterized the alternate regeneration trajectories in the absence of black spruce regeneration and examined possible abiotic factors driving those changes. We found evidence of alternate regeneration trajectories favouring tall shrub growth in sites experiencing a shortened fire return interval. Particularly, denser tall-shrub regeneration occurred in sites with deeper active layers. Increased shrub dominance may have implications on culturally significant species such as barren-ground caribou (Rangifer tarandus), berry producing plants, and those that depend on these species. Increased shrub growth will impact ecological processes like carbon sequestration, nutrient cycling, and permafrost dynamics. As disturbance regimes evolve, divergent post-fire successional pathways will continue to emerge, influencing other landscape processes, and impact important species to Indigenous communities of the area.

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