Low-severity fires in the boreal region: reproductive implications for black spruce stands in between stand-replacing fire events

• Published in: Annals of Botany
• Main Authors: Alfaro-Sánchez, Raquel, Johnstone, Jill F, Baltzer, Jennifer L
• Other Authors: Natural Science and Engineering Research Council Discovery
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2024
• Subjects: Northwest Territories; permafrost
• Online Access: http://dx.doi.org/10.1093/aob/mcae055; https://academic.oup.com/aob/advance-article-pdf/doi/10.1093/aob/mcae055/57360542/mcae055.pdf

Abstract Background and Aims Stand-replacing crown fires are the most prevalent type of fire regime in boreal forests in North America. However, a substantial proportion of low-severity fires are found within fire perimeters. Here, we aimed to investigate the effects of low-severity fires on the reproductive potential and seedling recruitment in boreal forest stands in between stand-replacing fire events. Methods We recorded site and tree characteristics from 149 trees within 12 sites dominated by mature black spruce [Picea mariana (Mill.) B.S.P.] trees in the Northwest Territories, Canada. The presence of fire-scarred trees supported classification of sites as unburned or affected by low-severity fires in recent history. We used non-parametric tests to evaluate differences in site conditions between unburned and low-severity sites. We used linear and additive statistical models to evaluate differences in tree age, size and reproductive traits among unburned trees and trees from low-severity sites. Key Results The results showed a significantly higher density of dead black spruce trees in low-severity sites and marginally significant higher presence of permafrost. Trees from low-severity fire sites were significantly older, exhibited significantly lower tree growth and showed a tendency towards a higher probability of cone presence and percentage of open cones compared with trees from unburned sites. Surviving fire-scarred trees affected by more recent low-severity fires showed a tendency towards a higher probability of cone presence and cone production. The density of black spruce seedlings increased significantly with recent low-severity fires. Conclusions Trees in low-severity sites appeared to have escaped mortality from up to three fires, as indicated by fire-scar records and their older ages. Shallow permafrost at low-severity sites might cause lower flammability, allowing areas to act as fire refugia. Low-severity surface fires temporarily enhanced the reproductive capacity of surviving trees and the ...