by Audrey Verreault | 23 October 2023
Published in Tree Genetics & Genomes 19(49). https://doi.org/10.1007/s11295-023-01625-7
Genetic parameters for growth, trunk quality, and susceptibility to frost and Sphaerulina musiva attack were estimated from 34 half-sib families of hybrid poplar from the crossing of non-native parents, Populus maximowiczii A. Henry, and Populus trichocarpa Torr. & Gray, 3 and 6 years after planting. The use of spatial analysis proved to be the best method for quantitative growth data. The proportion of the among-family variance to the total (phenotypic) variance as well as the high heritabilities of growth and susceptibility to frost and Spaherulina musiva showed a high potential for selection for these traits while the quality traits were under low genetic control. Some families showed gains for several traits, suggesting the possibility of developing a selection index to obtain superior families that show gain for not only growth but quality and adaptive traits as well. Type B correlations were high, suggesting that families responded in the same way regardless of the site. High type A correlation between growth traits at 3 and 6 years showed early selection potential, although these relationships should be confirmed with future measurements to evaluate this effect at maturity. These results can be integrated into the strategy for improving hybrid poplar parental populations and, in the longer term, will make it possible to optimize the selection of individuals with traits of interest for the operational deployment of hybrid poplar clones.
by Audrey Verreault | 12 October 2023
Published in Forest Ecology and Management 549: 121483. https://doi.org/10.1016/j.foreco.2023.121483
Forest management can enhance the ecosystem services forests provide, but it can also alter the capacity of forests to provide those services in the future. Ecosystem-based management has been widely implemented to mitigate the deterioration of forest ecosystems by reducing dissimilarities between managed and natural forests. Ecosystem-based management objectives generally aim to maintain community composition, stand structure, ecosystem functions and services. Heavy browsing pressure by ungulates at densities unrepresentative of past abundance could interfere with these objectives by chronically and selectively browsing tree regeneration following logging.
Using a browsing exclusion experiment, we investigated how the effects of different moose browsing pressures on tree regeneration could interfere with ecosystem management objectives in boreal forests of Quebec, Canada. Management objectives in this region include, among others, reaching targeted coniferous trees densities for commercial harvest, favouring the conservation of birches (Betula spp.) to maintain soil quality and conserving fruit-bearing trees due to their ecological significance for biodiversity. We used path analyses to differentiate direct and indirect effects of moose on seedling density and mixed models to investigate how browsing affected sapling recruitment and whether resulting densities are compatible with ecosystem management objectives.
By directly reducing the overall sapling density, moose browsing indirectly increased seedlings densities of all deciduous species. This indirect effect increased with browsing pressure and favoured raspberry cover, which was positively or negatively linked to seedling density, depending on tree species. Moderate and heavier browsing pressures reduced coniferous sapling density below the ecosystem management target. Moose suppressed birch saplings so that the minimal target of 50 birches ha−1 was not met under heavier browsing pressure. Sapling density of fruit-bearing trees was low under all browsing pressures when compared to exclosures.
Policy implications
Heavy moose browsing is preventing the achievement of ecosystem management objectives in our study area. Positive indirect effects on seedling densities suggest that reducing moose density could allow released seedlings to replenish the sapling layer, but we discuss why this would not guarantee reaching ecosystem management objectives. To help forest managers evaluate and respond to challenges posed by high ungulate densities, we suggest incorporating browsing inventories in national forest surveys to monitor this chronic disturbance and modulate decisions for forest ecosystem management.
by Audrey Verreault | 6 October 2023
Published in International Journal of Forest Research 2023: cpad045.https://doi.org/10.1093/forestry/cpad045
In northern hardwood forests, tree markers select the trees to be harvested during logging operations using classification systems that assign harvest priorities based on the presence of a wide range of individual defects. According to the most recent advances in our understanding of the impact of defects on both tree vigour (the risk of mortality or decline in growth) and quality (the potential for recovering valuable sawlogs), tree markers should adopt a simpler classification system that considers fewer defects than the current operational practice, and they should prioritize the removal of trees with crown dieback. Since the probability of developing defects and dying increases substantially with tree diameter, tree markers should also favour the removal of larger trees that have maintained their quality. However, these recommendations were developed based on tree-level analyses. To provide further validation at the stand scale, we compared stand improvement and value recovery under three tree marking regimes: a new, simplified regime based on the recommendations above, and two regimes used in the province of Quebec, Canada. To do so, we conducted tree marking simulations and value recovery assessments in 14 managed stands distributed across the northern hardwood range of Quebec. Our results confirmed that the simplified tree marking regime not only facilitated stand improvement by removing a greater proportion of low-vigour trees, but also recovered significantly more value (17% on average) at the stand scale. By prioritizing the removal of trees with crown dieback, the simplified regime was superior at salvaging the current value of low-vigour trees before they die or decline in quality. Based on our results, we propose simplified and empirically-validated tree marking guidelines for northern hardwood forests.
by Claire Morin | 18 September 2023
An aerial survey was conducted from February 8 to 25, 2022, over an area of 33,203 km², covering the Detour woodland caribou population’s winter range as delineated by the Québec government. This population, whose range overlaps the provinces of Québec and Ontario, has sometimes been referred to as the La Sarre herd or the Quebec-Ontario Frontier herd in Québec. A total of 338 animals were enumerated during the survey, including 83 in Québec and 255 in Ontario. At the time of the survey, calves accounted for roughly 22.4% of the population, giving a recruitment figure of 39.9 calves/100 females. The sex ratio was 37.8 males per 100 females. Based on detection rates estimated during the survey, the total abundance of the Detour population in winter 2022 would be between 446 and 465 individuals. This survey achieved the first abundance estimate for the entire cross-border Detour population. Comparison of the present results with those from earlier work is limited, since the latter covered only certain portions of the population’s range. Nevertheless, there are several indications that the Detour population has undergone a reduction in abundance since the 1980s.
by Audrey Verreault | 11 September 2023
Published in Forest Ecology and Management 545: 121304. https://doi.org/10.1016/j.foreco.2023.121304
Sugar maple (Acer saccharum Marshall) growth in the species’ southern range has been declining since the 1980s, putting at risk a variety of ecosystem services that the species provides. Heatwaves, drought, frosts, acidic deposition, and insect defoliation, all reducing photosynthetic activity, have been suggested to be behind the phenomenon. Because the geographic scope of previous studies on maple growth is limited to the southern temperate biome, it is not currently understood whether the same negative trends and factors affecting growth rates apply to the species in more northern regions of its distribution range. Here we used annual ring-width data of 1675 trees from a network of 21 sites in Quebec and Ontario between 45˚N and 48˚N to reconstruct maple growth and to analyze its trends and climatic drivers since 1950 CE. We developed a retrospective tree growth index by employing a Generalized Additive Mixed Model (GAMM) that accounted for tree age and size, terrain altitude, slope, competition and mean site climatology. Our reconstruction suggested considerable geographical variations in maple growth trends, with declining growth being less pronounced in the central portion of the study region. The growth decline persisted at the time of sampling in 2019 and 2020. Maple growth negatively correlated with the summer vapour pressure deficit (VPD) during both the previous and current growth seasons. As the decline in sugar maple growth is observed at the northern limit of its distribution, climate change may not favor the expansion of sugar maples to the north. The observed decline along with increasing VPD will likely have a negative impact on the ecosystem services supported by this species and calls for management adaptation measures.
