by Audrey Verreault | 17 April 2020
Published in Canadian Field-Naturalist 130(2): 133-136
The Eastern Red-backed Salamander (Plethodon cinereus) is well known for its colour polymorphism, which includes 8 colour phenotypes: the red-backed (striped), lead-backed (unstriped), and erythristic morphs, as well as the iridistic, albino, leucistic, amelanistic, and melanistic anomalies. Among these, the prevalence and geographic distribution of rare morphs have received little attention. In this article, we report 2 occurrences of silver-white variants of the red-backed morph of P. cinereus from Québec, Canada. To our knowledge, these variations in stripe colour on the red-backed phenotype represent the first 2 documented mentions for eastern Canada.
by Audrey Verreault | 17 April 2020
Published in Forestry 91(3): 259-270. doi: 10.1093/forestry/cpw059
Long-term success of forest management requires knowledge of standing tree characteristics and, an estimation of their evolution over time. In this study, hardwood stem quality was assessed using a specifically designed, non-destructive quality classification system that comprises four categorical output classes based on stem size and occurrence of external defects. We used data from national forest inventory sample plots distributed across Quebec (Canada) to predict hardwood stem quality and its evolution over time. We used ordinal logistic regression to model multiple stem quality classes. Hardwood stem quality was strongly related to stem harvest priority class and bioclimatic subdomain. Stem quality generally improved with d.b.h. and stand basal area. Changes in hardwood stem quality were strongly related to initial stem quality, with most trees retaining their initial quality over time. Stem quality evolution was also positively related to diameter growth. Overall, both initial and future stem quality were estimated with acceptable precision and minimal bias. Our results suggest that the equations could predict hardwood stem quality distribution and evolution among groups of forest stands.
by Marie-Claude Boileau | 17 April 2020
Published in Forest Science 63(1): 62-70. doi: 10.5849/forsci.15-178
Early successional competition among boreal forest tree and shrub species and its effects on growth of commercial tree species have been a major source of uncertainty in establishing efficient precommercial thinning and brushing prescriptions. We examined the effect of prethinning competitor density, postthinning competitor regrowth density, prethinning stem diameter, and the timing of thinning operations on the growth response of black spruce (Picea mariana [Mill.] BSP) and jack pine (Pinus banksiana Lamb.). In addition, we examined the mortality rate of hardwoods after thinning and the number of new shoots produced per surviving thinned stem. For jack pine, growth response was greatest when thinning occurred between 4 and 9 years after establishment, whereas for black spruce we observed no significant relationship between growth response and the timing of treatment. For jack pine, growth response was significantly affected by pretreatment competitor density, posttreatment competitor regrowth density, and pretreatment stem diameter. For black spruce, no significant relationship was observed between growth response and any variables. Mortality rates and production of new shoots in hardwoods varied significantly between species. Considering the high regrowth potential of willow (Salix spp.) and alder (Alnus spp.), we recommend that stands exhibiting low densities of these species should be left unthinned. Our results help foresters identify stands that require precommercial thinning and call for modification of currently used thinning strategies.
by Marie-Claude Boileau | 13 April 2020
Published in New Forests 47(6): 877–895
We studied three hybrid poplar plantations in Quebec (Canada) established on sites with varying soil and environmental characteristics to investigate the effects of logging residues on the water potential, carbon isotope ratio and foliar nutrients of planted trees. On each site, four treatments representing different residue loads, as well as treatments aimed at manipulating specific factors of the environment (Herbicide, Geotextile) were applied to test their effects on seedling water potential, carbon isotope ratio and foliar nutrients. Along with analyses of variance, we used structural equation modelling to infer causal relationships of logging residues on height, basal diameter and foliar nutrition of trees through their effects on soil temperature, soil water content and competing vegetation cover. Logging residues decreased soil temperature at all sites and woody plants cover at one site out of three. Height, basal diameter and unit leaf mass were strongly related to each other. Foliar d13C, N concentration and unit leaf mass increased with decreasing cover of woody plants suggesting an important role of competition for resources. Overall, logging residues had no direct influence on hybrid poplar dimensions after two growing seasons: their effects on the microenvironment of this resource demanding tree species were either cancelling out each other, or were not significant enough to have a significant impact on the growth drivers measured. For example, presence of logging residues might reduce soil temperature, impeding overall seedling performance. Our study highlights the fact that any given silvicultural method aimed at manipulating logging residues has a complex influence involving the interaction of multiple environmental drivers and that the net effect on tree productivity will depend on species and site specific conditions.
by Audrey Verreault | 13 April 2020
Published in Frontiers in Plant Science 7: 1450. doi: 10.3389/fpls.2016.01450
Because of changes in climatic conditions, tree seeds originating from breeding programs may no longer be suited to sites where they are currently sent. As a consequence, new seed zones may have to be delineated. Assisted migration consists of transferring seed sources that match the future climatic conditions to which they are currently adapted. It represents a strategy that could be used to mitigate the potential negative consequences of climate change on forest productivity. Decisions with regard to the choice of the most appropriate seed sources have to rely on appropriate knowledge of morpho-physiological responses of trees. To meet this goal, white spruce (Picea glauca [Moench] Voss) seedlings from eight seed orchards were evaluated during two years in a forest nursery, and at the end of the first growing season on three plantation sites located in different bioclimatic domains in Quebec. The morphophysiological responses obtained at the end of the second growing season (2+0) in the nursery made it possible to cluster the orchards into three distinct groups. Modeling growth curves of these different groups showed that the height growth of seedlings from the second-generation and southern first-generation seed orchards was significantly higher than that of those from other orchards, by at least 6%. A multiple regression model with three climatic variables (average growing season temperature, average July temperature, length of the growing season) showed that the final height of seedlings (2+0) from the first-generation seed orchards was significantly related to the local climatic conditions at the orchard sites of origin where parental trees from surrounding natural populations were sampled to provide grafts for orchard establishment. Seedling height growth was significantly affected by both seed source origins and planting sites, but the relative ranking of the different seed sources was maintained regardless of reforestation site. This knowledge could be used, in conjunction with transfer models, to refine operational seed transfer rules and select the most suitable sites in an assisted migration strategy.
