Wildfire promotes broadleaves and species mixture in boreal forest

• Published in: Forest ecology and management 2009-01, Vol.257 (1), p.343-350
• Main Authors: Chen, Han Y.H., Vasiliauskas, Stan, Kayahara, Gordon J., Ilisson, Triin
• Format: Article
• Language: English
• Subjects: Abies balsamea; Animal and plant ecology; Animal, plant and microbial ecology; basal area; Betula papyrifera; Biological and medical sciences; Boreal forest; boreal forests; botanical composition; Compositional difference; density; Direct regeneration; Fire; fire severity; forest growth; forest regeneration; forest stands; forest trees; Forestry; Fundamental and applied biological sciences. Psychology; montane forests; Picea glauca; Picea mariana; Pinus banksiana; Populus; Populus species; post-fire regeneration; prediction; species differences; species diversity; stand composition; statistical analysis; Synecology; Terrestrial ecosystems; tree and stand measurements; tree growth; wildfires
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2008.09.022

Postfire tree species compositions are predicted to be the same prior to fire according to the direct regeneration hypothesis (DRH). We studied 94 upland boreal forest stands between 5 and 18 years after fire in Ontario, Canada. Postfire species-specific regeneration density was positively related to prefire stand basal area for Pinus banksiana, Populus spp., Betula papyrifera and Picea mariana, but not for Picea glauca and Abies balsamea. In addition, seedling density of Populus spp., B. papyrifera, P. mariana, P. glauca and A. balsamea were positively affected by build up index and, except Populus spp., their density increased with age of burn. To facilitate testing the DRH, we introduced a term called compositional difference (CD) that is the difference in a species relative percentage between the postfire and prefire stand. The testable null hypothesis is CD = 0 for a given species. CD was not different from 0 for P. banksiana, was 19.8% for Populus spp., 10.4% for B. papyrifera, −17.9% for P. mariana, −14.6% for P. glauca, and −14.9% for A. balsamea, indicating fire increases broadleaves at the expenses of mid- and late-successional coniferous species. Compositional increases of Populus spp. and B. papyrifera in postfire stands occurred mostly where these species were a minor component prior to fire. In conclusion, the DRH was supported by the specific positive relationships between postfire regeneration densities and prefire basal area for P. banksiana, Populus spp., B. papyrifera and P. mariana. However, if the DRH is used for predicting postfire composition, P. banksiana is the only species that had the same composition between postfire and prefire stands. Nevertheless, CD for P. banksiana was negatively related to its prefire composition. Similarly, CD for other species was negatively related to their prefire compositions with varying effects of build up index and age of burn. Our results suggest, if fire occurrences increase with global change, the boreal landscape will be more dominated by hardwoods and mixtures of conifers and hardwoods.