by Audrey Verreault | 2 March 2021
Published in Trees 35(1). https://doi.org/10.1007/s00468-020-02001-x
Some studies suggest that tapping sugar maple (Acer saccharum Marshall) trees can cause their growth to decline, particularly on poor and acidic soils. We tested this hypothesis in seven sugar bushes located in the Quebec Appalachians by comparing the growth of tapped trees with nearby untapped trees. The sites represented a range of soil fertility, from very good for sugar maple to strongly deficient in calcium. Trees were cored, and individual dendrochronology series were used to analyze trends in basal area growth, from a period of 10 years before, to 8–10 years after tapping began. Basal area growth of sugar maples did not appear to be influenced by tapping (p ≥ 0.134), except at one site (p < 0.001), where the growth of tapped trees decreased by 33% over 10 years. This decline could not be explained only by the poor soil fertility observed at the site. Although a tree biomass distribution budget indicated that maple syrup production represented only 4–6% of the carbon allocated annually to net primary production, the long-term relationship between maple syrup production and tree growth requires further study.
by Audrey Verreault | 2 March 2021
Published in Energies 14(1): 93. https://doi.org/10.3390/en14010093
Unharvested hardwoods are abundant in eastern Canada, due to the low quality of their fiber and the absence of outlets in conventional wood transformation industries. The objective of this study was to assess the biochemical and thermochemical energy conversion potential of decaying hardwoods and compare their relationships with external and internal indicators of tree degradation. We characterized how wood-decay processes altered the physical and chemical properties of these woods and affected their digestibility yield and their performance according to indexes of stability and efficiency of combustion. DNA analysis on wood samples was also performed to determine the relative abundance of white-rot fungi compared to that of other saprotrophs. All properties stayed within the range of variations allowing the wood to remain suitable for conversion into bioenergy, even with increased decay. We found no significant differences in the physical and chemical properties that are crucial for energy production between wood from externally-assessed live and decayed trees. However, the proportion of wood area affected by rot was significantly associated with increased digestibility yield, and with decreased combustion reactivity. We could not detect any specific effect associated with increased relative abundance of white-rot fungi. These results suggest that the utilization of biomass from decayed hardwoods instead of live trees for bioenergy production should not alter the conversion efficiency and even potentially increase the performance of biochemical pathways, and hence, support their use as feedstock for bioenergy production.
by Marie-Claude Boileau | 4 February 2021
Publish in Forest Science 65(4): 411-419
The management of sugar maple (Acer saccharum) at the northern edge of its range is mainly oriented toward timber production, from trees of higher grades. However, both the quality of mature trees in natural stands and how the quality may vary depending on the silvicultural treatment are unknown, especially under northern conditions. The objective of this study was to describe the variation in stem quality of mature maple trees (diameter >33 cm) according to climatic, geographic or soil variables, and to evaluate the effects of a first selection cutting cycle on this quality. Annual temperature (1.7–4.1° C) was the most important variable explaining differences in the proportion of higher-grade trees, with a 16 percent gain associated with every additional increase in degrees Celsius. The practice of a first selection cutting was associated with an 11 percent gain in this proportion. Although the actual proportion of high-quality trees was below 35 percent on the coolest sites, a proper tree selection through silviculture could likely improve this proportion in future decades, whereas the potential effects of climate change are unclear.
by Marie-Claude Boileau | 3 February 2021
Published in Forest Ecology and Management 476: 118460. https://doi.org/10.1016/j.foreco.2020.118460
In boreal forests where the fire return interval is long, the high structural variability of stands may affect wood traits. Here, we build on earlier work that revealed a difference in wood mechanical traits of black spruce between regular (regenerated from fire in the last 200 years) and irregular (undisturbed by fire for at least 200 years) stands. This study aimed to identify the ecological drivers of this variation in wood traits. To do so, we first sought to corroborate existing results on the effects of stand structure induced by the time since the last stand-replacing fire (TSLF) on wood mechanical stiffness in the eastern boreal forest of Canada. Results confirmed that black spruce from regular stands tend to produce wood with higher modulus of elasticity (MOE) than those from irregular stands. For both regular and irregular stands, we compared a set of linear models that were defined a priori to determine the structural and site productivity variables having the largest influence on MOE. The ‘growth efficiency index’ (aboveground woody biomass production per unit leaf area) was the best predictor of MOE variation among regular stands. For irregular stands, the model with TSLF as the sole explanatory variable was a better predictor of MOE than any other candidate model. However, we did not find strong evidence of a direct relationship between TSLF and wood traits, since our best models explained a relatively small proportion of the variance. Our results suggest that differences in wood traits could be attributable to the seed or layer origin of the trees and/or to the length of time trees remain in the understory. We propose that intensive wood production strategies focus on stands of the first post-fire cohort.
by Claire Morin | 2 February 2021
Published in Forest Ecology and Management 481: 118744. https://doi.org/10.1016/j.foreco.2020.118744
Over the last century, forest management has modified the natural disturbance regime of temperate and boreal forest regions. Consequently, this new disturbance regime may have profoundly affected the structure, composition and associated carbon stocks of forest ecosystems. The aim of this study is to document structural and compositional changes (1925–2015) in an actively managed forest region of eastern North America and their effects on above-ground biomass (AGB). We reconstructed stand structure, species composition and AGB of the preindustrial forest using 54,343 plots sampled by the Price Brothers & Company from 1924 to 1930. The present-day forest was described using 9561 plots surveyed during the most recent decadal forest inventories (1980s, 1990s, 2000s, 2010s) conducted by the Government of Quebec, eastern Canada. Between 1925 and 2015, the age structure shifted from a dominance of old-growth and mature stands (>80 years) to one of immature stands (<40 years) where early successional deciduous species increased in importance. The most striking difference was the sharp increase in stand density (>72%). Accordingly, tree diameter distribution changed markedly as a result of a strong increase of the smallest tree class to the expense of larger tree classes. Despite this structural reorganization, AGB has remained stable. Forest management history has induced a major forest structure reorganization. Aerial carbon stocks remain stable and resilient despite the strong density increase of small trees. The sharp increase in stand density could have significant impacts on biodiversity and resilience. In accordance with ecological forestry principles, the restoration of more natural forest conditions is expected to reduce the possible detrimental effects of forest management.
