by Claire Morin | 30 January 2019
Published in Journal of Biogeography 44(6): 1268-1279. https://doi.org/10.1111/jbi.12921
Aim Wildfire activity is projected to increase under global warming in many parts of the world. Knowledge of the role of these disturbances in shaping the composition of boreal forests is needed to better anticipate their future impacts. Here, we investigate the incidence of wildfire activity (burned biomass, frequency and size) on multi-millennia vegetation trajectories in two coniferous boreal forest regions that display different types of vegetation composition and relief. We hypothesize that this difference in vegetation results from dissimilar wildfire activity during the Holocene. Location Conifer-dominated boreal forests in Quebec-Labrador, eastern North America. Methods Fire and vegetation histories during the last 8000 years were reconstructed and compared through analyses of charcoal and pollen records extracted from nine lacustrine deposits located in two spruce-moss forests: the western region, co-dominated by Pinus banksiana, and the eastern region, co-dominated by Abies balsamea. Results Between 7000 and 2000 cal. yr bp, the western region experienced fewer fires than the eastern region, but they were larger in size. The main species adapted to fire, P. banksiana and Alnus viridis ssp. crispa, progressively co-dominated with Picea sp.. Conversely, in the eastern region, P. banksiana and A. viridis ssp. crispa were very rare, and Picea sp. co-dominated with non-fire-adapted A. balsamea and Betula sp.. Then, around 2000 cal. yr bp, fires decreased in frequency but were larger in size in the eastern region than in the western one, thus allowing densification of P. banksiana and A. viridis ssp. crispa in these landscapes. Main conclusions In the coniferous boreal forests of eastern North America, fire size was relatively more important in determining the long-term vegetation trajectories in comparison with fire frequency. Changes in the rate of occurrence of large-fire episodes will have significant impacts on vegetation dynamics over the next decades under continuing warming.
by Marie-Claude Boileau | 30 January 2019
Published in Journal of Forestry Research 28(3): 95-106. https://doi.org/10.1007/s11676-018-0778-3
We studied late-entry commercial thinning effects on growth, yield, and regeneration in a 48-year-old jack pine (Pinus banksiana Lamb.) stand. Applied thinning intensities were 27, 32, and 47% of merchantable basal area (BA) excluding skidding trails. After 15 years, mean diameter at breast height of surviving trees in the 47% BA removal increased by 4.9 cm (25%) compared to the unthinned control. The 47% BA removal also increased gross merchantable volume (GMV) tree−1 by 46% compared to the control. The 27% BA removal had twice as much GMV ha−1 compared to the 47% BA removal after 15 years. Moreover, cumulative GMV ha−1 was much higher in the 27% BA removal than in the unthinned control. The highest thinning intensity produced larger trees on average, while the lowest thinning intensity maximized volume production per hectare. Maintenance of acceptable growing stock throughout the 15-year period in the 27% BA removal could provide other ecosystem functions such as biodiversity enhancement or wildlife habitat by delaying senescence. Regeneration data showed that a shift in species composition occurred in the understory. After 15 years, the understory was dominated by black spruce (Picea mariana (Mill.) B.S.P.), white birch (Betula papyrifera Marsh.), and trembling aspen (Populus tremuloides Michx.). If regenerating jack pine is an objective after final overstory removal, additional efforts will be needed to re-establish this species.
by equipewp | 30 January 2019
Published in Quat. Sci. Rev. 193: 312-322.
by Claire Morin | 30 January 2019
Published in Forests 9(8): 471. https://doi.org/10.3390/f9080471
Natural disturbances are fundamental to forest ecosystem dynamics and have been used for two decades to improve forest management, notably in the boreal forest. Initially based on fire regimes, there is now a need to extend the concept to include other types of disturbances as they can greatly contribute to forest dynamics in some regions of the boreal zone. Here we review the main descriptors—that is, the severity, specificity, spatial and temporal descriptors and legacies, of windthrow and spruce bud worm outbreak disturbance regimes in boreal forests—in order to facilitate incorporating them into a natural disturbance-based forest management framework. We also describe the biological legacies that are generated by these disturbances. Temporal and spatial descriptors characterising both disturbance types are generally variable in time and space. This makes them difficult to reproduce in an ecosystem management framework. However, severity and specificity descriptors may provide a template upon which policies for maintaining post harvesting and salvage logging biological legacies can be based. In a context in which management mainly targets mature and old-growth stages, integrating insect and wind disturbances in a management framework is an important goal, as these disturbances contribute to creating heterogeneity in mature and old-growth forest characteristics.
