by Marie-Claude Boileau | 30 January 2019
Published in Tree Physiology 34(2): 194-204. doi: 10.1093/treephys/tpt114
We examined the ecophysiology and growth of 0.31.3 m tall advance red spruce (Picea rubens Sarg.) and balsam fir (Abies balsamea [L.] Mill.) regeneration during a 5-year period following the application of different harvest types producing three sizes of canopy openings: (i) small gaps (<100 m2 in area; SMA) created by partial uniform single-tree harvest; (ii) irregular gaps of intermediate size (100300 m2; INT) created by group-selection harvest (removal of groups of trees, mainly balsam fir, with uniform partial removal between groups); and (iii) large circular gaps (700 m2; LAR) created by patch-selection harvest (removal of trees in 30-m diameter circular areas with uniform partial removal between gaps). An unharvested control (CON) was monitored for comparison. At the ecophysiological level, we mainly found differences in light-saturated photosynthesis of red spruce and specific leaf area of balsam fir among treatments. Consequently, we observed good height growth of both species in CON and INT, but fir surpassed spruce in SMA and LAR. Results suggest that intermediate 100–300 m2 irregular openings create microenvironmental conditions that may promote short-term ecophysiology and growth of red spruce, allowing the species to compete with balsam fir advance regeneration. Finally, results observed for spruce in large 700-m2 openings confirm its inability to grow as rapidly as fir in comparable open conditions.
by Marie-Claude Boileau | 30 January 2019
Published in Forestry 87: 153-164. https://doi.org/10.1093/forestry/cpt048
It is necessary to evaluate how large seedling stock, used as an alternative to chemical herbicide for vegetation management, interacts with the timing of mechanical release (MR) and if use of such stock offers a broader window of intervention for release than conventional stock. Such a context is present in Quebec (Canada), where chemical herbicides were banned from use on public lands in 2001.We thus evaluated the impact of delaying MR on the performance of large spruce seedlings established in a gradient of vegetation zones and competition environments. Fourteen experiments were conducted in Picea glauca or P. mariana plantations in the temperate hardwood (TH), temperate mixedwood or boreal mixedwood vegetation zones. On each site, we established a completely randomized block design with 5–8 replicates, each divided into four plots: (1) control; (2) MR applied the year during which light availability to the planted seedlings averaged 60 per cent of full sunlight (EARLY); (3) MR at EARLY + 1 year (LATE1); and (4) MR at EARLY + 2 years (LATE2). Vegetation data collected in controls 8 years after MR was submitted to a correspondence analysis to group the sites according to their competing species dominance. Seedling responses to the timing of MR, 5–8 years after treatment, varied across competing vegetation dominance, vegetation zone or a combination of both.On sites where intolerant hardwoods were dominant, postponing MR 1 year after light availability had reached 60 per cent of full sunlight had a positive effect on seedling dimensions, especially in the TH zone. However, the LATE2 treatment resulted in significant stem volume losses on these sites. Whereas treatment effects were limited on ericaceous dominated sites, MR promoted seedling growth on sites dominated by shrub/herbaceous species, with no difference between EARLY, LATE1 and LATE2.
by André Boily | 30 January 2019
Proceedings published in Digital Soil Assessments and Beyond. Minasny, B., B.P. Malone et A.B. McBratney (eds.). April 10-13, 2012. Sydney, Australie. p. 381-386.
by Audrey Verreault | 30 January 2019
Published in Canadian Journal of Forest Research 42: 1289-1305
The dynamics of high-altitude balsam fir (Abies balsamea (L.) Mill.) forests is mainly driven by insect outbreaks and windthrows. However, very little work has been done on the role of fire on the development and maintenance of this ecosystem. In this study, we document the role of fire in the high-altitude balsam fir forests of the Réserve Faunique des Laurentides (RFL), southern Quebec. Sixteen sites were sampled among six different forest types described according to plant composition and fire evidence.
At each site, the diameter structure was recorded and stand age was calculated based on tree-ring dating of individual trees and radiocarbon-dated surficial charcoal samples. Fire played a major role in the recent dynamics of high-altitude fir forests in the RFL. Over the last 250 years, nearly 50% of the study area burned during two fire conflagrations, i.e., around 1815 and in 1878. The fires triggered gradual changes in plant composition and forest structure, as shown by a succession of forest types ranging from white birch (Betula papyrifera Marsh.) to spruce–fir types. Absence of surficial charcoal older than 300 years suggests that high-altitude forests of the RFL area were not subjected to a constant fire regime. It is possible that recent fires were caused by human activity.
by Claire Morin | 30 January 2019
Published in Soil Biology and Biochemistry 64: 174-180
During the last several decades, colonization of soil by exotic earthworms and their effects on soil properties and biodiversity have been reported in forests of North America. In some northern hardwood stands, acid soils or harsh climate may have prevented earthworm colonization. However, climatic change and the increasing use of liming to restore the vigor of declining sugar maple (Acer saccharum Marsh.) stands, situated on base-poor soils in USA and Canada, could make many of these sites more suitable for earthworm colonization. We tested survival and reproduction of two exotic earthworm species (Lumbricus terrestris and Amynthas hawayanus) in unlimed and limed soils at the northern limit of the northern hardwood forest distribution in Canada. Improving soil parameters of base-poor, acidic soils by liming positively influenced activity, survivability and reproductive output of L. terrestris in this northern hardwood forest. In contrast, the high mortality and low vigor of L. terrestris observed in the unlimed plots show that soils in this area with a pH of 4.3 are not favorable to this species. Our results suggest that A. hawayanus was very active prior to winter at both soil pHs, but was not able to complete its life cycle during one year at this latitude. Both earthworm species significantly reduced organic C and total N, and increased the C/N ratio of the forest floor. Given that forest liming activities are increasing in proximity to human activities, there is high probability that some earthworm species, such as L. terrestris, will invade limed northern hardwood forests in the next decades, with possible consequences for soil organic matter turnover, nutrient cycling and forest biodiversity and dynamics.
