by Marie-Claude Boileau | 7 October 2020
Published in Canadian Journal of Forest Research 49(12): 1516-1524. https://doi.org/10.1139/cjfr-2018-0409
The increased pressure on timber supply due to a reduced forest land base urges the development of new approaches to fully capture the value of forest products. This paper investigates the effects of knowing the position of knots on lumber volume, value, and grade recoveries in curve sawing of 31 white spruce (Picea glauca (Moench) Voss) and 22 jack pine (Pinus banksiana Lamb.) trees. Internal knot position was evidenced by X-ray computed tomography (CT) imaging, followed by the application of a knot-detection algorithm allowing log reconstruction for use as input in the Optitek sawing simulation software. Comparisons of the three levels of sawing optimization (sweep up, shape optimized, and knot optimized) revealed that considering internal knots before log sawing (e.g., knot optimized) generated 23% more lumber value for jack pine and 15% more for white spruce compared with the traditional sweep-up sawing strategy. In terms of lumber quality, the knot-optimized strategy produced 38% more pieces of grade No. 2 and better in jack pine and 15% more such pieces in white spruce compared with the sweep-up strategy. These results indicate a great potential to increase manufacturing efficiency and profitability by implementing the CT scanning technology, which should aid in developing a strong bioeconomy based on an optimized use of wood.
by Marie-Claude Boileau | 7 October 2020
Published in Forest Ecology and Management 458: 117801. https://doi.org/10.1016/j.foreco.2019.117801
Boreal ericaceous shrubs, such as Kalmia angustifolia, have evolved various traits allowing them to interfere with the growth of conifer trees. These include the ability to spread through rhizomatous growth and to produce high amounts of tannins that interfere with soil N cycling. We examined how pre-commercial thinning (PCT) of young black spruce (Picea mariana) stands, a common silvicultural practice, increases the aboveground and belowground spread of various ericaceous shrubs, the chemical quality of leaves and litter, as well as soil nitrogen cycling. We compared these effects in relatively cool-moist and relatively warm-dry climates. Within the warm-dry climate, we also compared the effects of PCT on fertile clay and on nutrient-poor till deposits. The total cover of ericaceous shrubs was higher in PCT than in control plots in all three site types. On nutrient poor till deposits (in both climates), the current-year rhizome length and specific rhizome mass of K. angustifolia were higher in PCT than in control plots. Soil mineralizable NH4+-N was lower under patches of K. angustifolia than under patches of feather moss (Pleurozium schreberi). Across all 24 plots, canopy openness had a positive relationship with ericaceous shrub cover, current-year rhizome length, foliar tannins and phenolic concentrations. Although PCT might increase tree growth in the short-term, its positive effects on ericaceous shrubs increases the risk of conifer seedling growth check when the next clearcut harvest occurs, especially in cool moist climates and on nutrient poor soil deposits.
by Claire Morin | 7 October 2020
Published in PLOS ONE 14(12): e0226909. https://doi.org/10.1371/journal.pone.0226909
The forest floor of boreal forest stores large amounts of organic C that may react to a warming climate and increased N deposition. It is therefore crucial to assess the impact of these factors on the temperature sensitivity of this C pool to help predict future soil CO2 emissions from boreal forest soils to the atmosphere. In this study, soil warming (+2–4°C) and canopy N addition (CNA; +0.30–0.35 kg·N·ha-1·yr-1) were replicated along a topographic gradient (upper, back and lower slope) in a boreal forest in Quebec, Canada. After nine years of treatment, the forest floor was collected in each plot, and its organic C composition was characterized through solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Forest floor samples were incubated at four temperatures (16, 24, 32 and 40°C) and respiration rates (RR) measured to assess the temperature sensitivity of forest floor RR (Q10 = e10k) and basal RR (B). Both soil warming and CNA had no significant effect on forest floor chemistry (e.g., C, N, Ca and Mg content, amount of soil organic matter, pH, chemical functional groups). The NMR analyses did not show evidence of significant changes in the forest floor organic C quality. Nonetheless, a significant effect of soil warming on both the Q10 of RR and B was observed. On average, B was 72% lower and Q10 45% higher in the warmed, versus the control plots. This result implies that forest floor respiration will more strongly react to changes in soil temperature in a future warmer climate. CNA had no significant effect on the measured soil and respiration parameters, and no interaction effects with warming. In contrast, slope position had a significant effect on forest floor organic C quality. Upper slope plots had higher soil alkyl C:O-alkyl C ratios and lower B values than those in the lower slope, across all different treatments. This result likely resulted from a relative decrease in the labile C fraction in the upper slope, characterized by lower moisture levels. Our results point towards higher temperature sensitivity of RR under warmer conditions, accompanied by an overall down-regulation of RR at low temperatures (lower B). Since soil C quantity and quality were unaffected by the nine years of warming, the observed patterns could result from microbial adaptations to warming.
by Claire Morin | 7 October 2020
Published in The Forestry Chronicle 95(3): 196-206. https://doi.org/10.5558/tfc2019-028
Forest managers have to take into account multiple objectives such as stand yield, wood quality attributes, ecological constraints and social considerations when making their decisions. The objective of the present study is to build
(i) a dynamic modulus of elasticity (MOEdyn) model and
(ii) a core wood density (WDcore) model for white spruce plantations in the Bas-Saint-Laurent Region (Québec, Canada) to quantify their inter- and intra-stand variations in order for managers to better weigh their different options.
Using data obtained from 54 sample plots in 31 white spruce plantations from Eastern Québec, the MOEdyn of 143 trees and the WDcore of 162 trees were analysed. Dendrometric and stand variables were used to build a MOEdyn linear mixed-effect model and a WDcore multiple linear regression model. The MOEdyn model explained 66.8% of the total variation, 1.1% of which originated from inter-stand variations. MOEdyn was proportional to diameter at breast height (DBH) and non-linearly decreased with tree growth rate. The WDcore model explained 16.0% of the total variation. The intra-stand variations were represented by a negative relationship between WDcore and growth rate. Inter-stand variations were accounted for by site index and altitude. The performance of the MOEdyn model was satisfactory and in accordance with the literature. However, the WDcore model was below standard, mainly as a consequence of unaccounted intra-individual variations. Nonetheless, raw simulations using these models suggest that white spruce wood from plantations may benefit from intensive forest management.
by Audrey Verreault | 7 October 2020
Published in Journal of Chemical Ecology 46(1): 84-98. https://doi.org/10.1007/s10886-019-01130-z
Non-nutritive phytochemicals (secondary metabolites and fibre) can influence plant resistance to herbivores and have ecological impacts on animal and plant population dynamics. A major hindrance to the ecological study of these phytochemicals is the uncertainty in the compounds one should measure, especially when limited by cost and expertise. With the underlying goal of identifying proxies of plant resistance to herbivores, we performed a systematic review of the effects of non-nutritive phytochemicals on consumption by leporids (rabbits and hares) and cervids (deer family). We identified 133 out of 1790 articles that fit our selection criteria (leporids = 33, cervids = 97, both herbivore types = 3). These articles cover 18 species of herbivores, on four continents. The most prevalent group of phytochemicals in the selected articles was phenolics, followed by terpenes for leporids and by fibre for cervids. In general, the results were variable but phenolic concentration seems linked with high resistance to both types of herbivores. Terpene concentration is also linked to high plant resistance; this relationship seems driven by total terpene content for cervids and specific terpenes for leporids. Tannins and fibre did not have a consistent positive effect on plant resistance. Because of the high variability in results reported and the synergistic effects of phytochemicals, we propose that the choice of chemical analyses must be tightly tailored to research objectives. While researchers pursuing ecological or evolutionary objectives should consider multiple specific analyses, researchers in applied studies could focus on a fewer number of specific analyses. An improved consideration of plant defence, based on meaningful chemical analyses, could improve studies of plant resistance and allow us to predict novel or changing plant-herbivore interactions.
