by Audrey Verreault | 30 January 2019
Published in Tree Seed Working Group – News Bulletin. Canadian forest genetics association. 50(December): 15-17. https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/forestry/tree-seed/tree-seed-centre/tswgnewsbulletin50.pdf
Water activity (aw ) is a non-destructive, portable, and rapid technique currently used to assess the moisture of hygroscopic materials (e.g., agro-food, pharmaceuticals) and particularly, one of intermediate products such as orthodox seeds (Baldet et al. 2007).
by Audrey Verreault | 30 January 2019
Published in Canadian Field-Naturalist 123(3): 210-214
Artificial cover objects or coverboards have been widely used to study Eastern Red-backed Salamanders (Plethodon cinereus), a species that is very abundant in eastern North America and known to be one of the most common vertebrates within its geographical range. However, recent studies have suggested that potential bias may be associated with the use of coverboards compared with natural cover objects. In this study, age structure and body size (weight and snout-vent length, SVL) of P. cinereus found under coverboards and natural cover objects at Lake Clair (Quebec, Canada) were compared. Coverboards were made of Sugar Maple (Acer sacchrum), a native forest species dominant in the study area. In 2004 and 2005, a total of 162 P. cinereus were found under coverboards, and 156 P. cinereus were found under natural cover objects. No significant difference in the age structure, mean weight, or SVL of P. cinereus was observed between the two sets. This study suggests that the type of coverboard used at Lake Clair is a good method to obtain an accurate index of P. cinereus population demographics, and is similar to that expected under natural cover objects. This technique should help to establish a standard protocol that could better allow direct comparisons among studies in the future. However, more studies are needed to explain the high proportion of adult specimens found under both cover types at Lake Clair relative to studies in other regions in North America.
by Audrey Verreault | 30 January 2019
Published in Tree Genetics & Genomes 7: 641-653
We investigated the influence of cambial age on correlations between different wood traits and the possibility of early selection in order to help decision-making for the improvement of juvenile wood in white spruce (Picea glauca (Moench) Voss). Increment cores were analysed from 375 trees covering 25 open-pollinated families from a 30-year-old provenance–progeny trial in Quebec, Canada. Genetic and phenotypic correlations between different mechanical and fibre anatomy-related wood traits were found to vary with cambial age. Most correlations became stronger in magnitude in rings closer to the bark. An exception is the correlation between microfibril angle (MFA) and the modulus of elasticity where correlations were strongly negative from the pith to the bark. Age–age correlations for different wood traits were found to be high and possible gains from early selection were estimated to be good in ring 8 and older for most traits. MFA was the trait with the strongest potential for selection as early as ring 4, but a detrimental correlation with wood density may represent a drawback of such a juvenile selection approach. Estimates showed that selection concentrated on a few easily measurable traits such as wood density and core length holds promise to obtain superior genetic gains for mechanical properties, but negative impacts would be expected on fibre anatomy traits related to pulp quality. These findings show the need for more carefully planned breeding and selection strategies if one wishes to improve several traits for different end uses.
by Svetlana Savin | 30 January 2019
Published in Environmental Modelling & Software 26(3): 280-288
The predictions from most forest ecosystem models originate from deterministic simulations. However, few evaluation exercises for model outputs are performed by either model developers or users. This issue has important consequences for decision makers using these models to develop natural resource management policies, as they cannot evaluate the extent to which predictions stemming from the simulation of alternative management scenarios may result in significant environmental or economic differences. Various numerical methods, such as sensitivity/uncertainty analyses, or bootstrap methods, may be used to evaluate models and the errors associated with their outputs. However, the application of each of these methods carries unique challenges which decision makers do not necessarily understand; guidance is required when interpreting the output generated from each model. This paper proposes a decision flow chart in the form of an analytical framework to help decision makers apply, in an orderly fashion, different steps involved in examining the model outputs. The analytical framework is discussed with regard to the definition of problems and objectives and includes the following topics: model selection, identification of alternatives, modelling tasks and selecting alternatives for developing policy or implementing management scenarios. Its application is illustrated using an on-going exercise in developing silvicultural guidelines for a forest management enterprise in Ontario, Canada.
by Audrey Verreault | 30 January 2019
Published in Canadian Journal of Forest Research 37: 2106-2114
Tree-ring chronologies have been widely used in studies of tree mortality where variables of recent growth act as an indicator of tree physiological vigour. Comparing recent radial growth of live and dead trees thus allows estimating probabilities of tree mortality. Sampling of mature dead trees usually provides death-year distributions that may span over years or decades. Recent growth of dead trees (prior to death) is then computed during a number of periods, whereas recent growth (prior to sampling) for live trees is computed for identical periods. Because recent growth of live and dead trees is then computed for different periods, external factors such as disturbance or climate may influence growth rates and, thus, mortality probability estimations. To counteract this problem, we propose the truncating of live-growth series to obtain similar frequency distributions of the “last year of growth” for the populations of live and dead trees. In this paper, we use different growth scenarios from several tree species, from several geographic sources, and from trees with different growth patterns to evaluate the impact of truncating on predictor variables and their selection in logistic regression analysis. Also, we assess the ability of the resulting models to accurately predict the status of trees through internal and external validation. Our results suggest that the truncating of live-growth series helps decrease the influence of external factors on growth comparisons. By doing so, it reinforces the growth-vigour link of the mortality model and enhances the model’s accuracy as well as its general applicability. Hence, if model parameters are to be integrated in simulation models of greater geographical extent, truncating may be used to increase model robustness.
