Canadian Forest Service Publications

Burn severity dominates understory plant community response to fire in xeric jack pine forests. 2016. Pinno, B.D.; Errington, R.C. Forests 7(4):83.

Year: 2016

Issued by: Northern Forestry Centre

Catalog ID: 36752

Language: English

CFS Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.3390/f7040083

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Abstract

Fire is the most common disturbance in northern boreal forests, and large fires are often associated with highly variable burn severities across the burnt area. We studied the understory plant community response to a range of burn severities and pre-fire stand age four growing seasons after the 2011 Richardson Fire in xeric jack pine forests of northern Alberta, Canada. Burn severity had the greatest impact on post-fire plant communities, while pre-fire stand age did not have a significant impact. Total plant species richness and cover decreased with disturbance severity, such that the greatest richness was in low severity burns (average 28 species per 1-m2 quadrat) and plant cover was lowest in the high severity burns (average 16%). However, the response of individual plant groups differed. Lichens and bryophytes were most common in low severity burns and were effectively eliminated from the regenerating plant community at higher burn severities. In contrast, graminoid cover and richness were positively related to burn severity, while forbs did not respond significantly to burn severity, but were impacted by changes in soil chemistry with increased cover at pH >4.9. Our results indicate the importance of non-vascular plants to the overall plant community in this harsh environment and that the plant community is environmentally limited rather than recruitment or competition limited, as is often the case in more mesic forest types. If fire frequency and severity increase as predicted, we may see a shift in plant communities from stress-tolerant species, such as lichens and ericaceous shrubs, to more colonizing species, such as certain graminoids.

Plain Language Summary

Fire is the most common disturbance in northern boreal forests, and large fires often burn within consistent degrees of intensity. Four growing seasons after the 2011 Richardson Fire, we studied the understory plant community response to a range of fire intensities and pre-fire stand age in dry jack pine forests of northern Alberta, Canada. Burn severity (the fire’s degree of intensity) had the greatest effect on post-fire plant communities while pre-fire stand age did not have a significant effect. Total plant richness and cover decreased with the severity of the disturbance. However, the response of individual plant groups differed. Lichens and mosses were most common in areas where low severity fires burned and were effectively eliminated from the regenerating plant community in areas that experienced more intense fires. In contrast, the cover and richness of grasses were positively related to burn severity, while other types of plants did not respond significantly to severe burns but were affected by changes in soil chemistry. Our results indicate the importance of non-vascular plants to the overall plant community in this harsh environment and that the plant community is limited by environmental constraints rather than being limited by newly introduced plants or competition from other plants, as is often the case in moderately moist forest types. If fire frequency and intensity increases as predicted, we may see a shift in plant communities from stress-tolerant species such as lichens and some shrubs to more colonizing species such as certain grasses.