by Audrey Verreault | 8 December 2022
Published in Canadian Journal of Forest Research 52(12): 1499-1512. https://doi.org/10.1139/cjfr-2022-0092
The reproductive ecology of the semi-serotinous species black spruce (Picea mariana (Mill.) BSP) in northern boreal forests remains poorly understood. There is a general lack of data on cone/seed production and viability as a function of biotic treelevel characteristics and abiotic variables. No studies currently exist to quantify these differences over a large gradient in temperature, elevation, and precipitation. Extensive physical, ecological, dendrometric, and reproductive data were collected from young to very old black spruce stands in northern Quebec. ANOVA and general linear mixed models were used to examine interannual cone production, and the relative importance of the biotic and abiotic explanatory factors in determining total cone production; length of the cone-bearing zone; filled seeds per cone; proportion of filled seeds; and seed viability. The results illustrate that the reproductive ecology of black spruce in northern cold forests is mainly explained by biotic variables such as age and diameter at breast height, and by abiotic variables related to temperature such as elevation, length of the growing season, and growing degree-days. Black spruce exhibits a lower reproductive potential in northern cold forests, making it possibly less resilient to increased fire frequency, particularly in unproductive and very young or very old stands.
by Audrey Verreault | 2 December 2022
Published in Forests 13(12): 1975. https://doi.org/10.3390/f13121975
In recent decades, forest nurseries in eastern Canada have been faced with periods of mild winter weather, delayed snowfall, and low seedling protective snow cover combined with winter rains instead of snowfall. These extreme conditions have resulted in the loss of millions of seedlings, in particular those that overwinter outdoors, probably due to their winter dehardening. The main objective of this study is to simulate different periods of warm weather at the beginning and end of winter and evaluate their effects on the dehardening and growth of Picea mariana and Picea glauca seedlings in response to different freezing temperatures. Three warming treatments were simulated (control, 1 day, and 3 days of warming at 10 C) followed by three freezing temperatures (?4, ?12, and ?20 C). In winter, regardless of the warming treatment, the seedlings of the two species tolerated the different freezing temperatures without any apparent damage. However, at the end of winter and in the absence of snow cover, the seedlings did not show frost tolerance at ?20 C. On the other hand, the seedlings showed normal growth after undergoing frosts at ?4 C and ?12 C, similar to that observed for control seedlings. Different cultural practices and protection strategies are proposed to improve frost tolerance and reduce the winter loss of seedlings.
by Audrey Verreault | 16 November 2022
Published in Forests 2022(13): 1926. https://doi.org/10.3390/f13111926
Eastern spruce budworm (Choristoneura fumiferana Clem.) is considered the most important disturbing insect in coniferous stands in eastern North America. During an outbreak, spruce budworm can cause severe defoliation in balsam fir (Abies balsamea (L.) Mill.), which can affect wood properties such as moisture content and mechanical properties. This project aimed to assess the influence of the duration of spruce budworm defoliation on the wood quality of mature balsam fir trees. To do this, we studied sapwood proportion, decay, moisture content, mechanical properties and tracheid dimensions in stands that had suffered three, four or five years of defoliation. We also compared living and dead balsam firs and evaluated the change in wood properties with time. Our results showed that dead balsam firs suffered from a loss of wood quality rapidly after their death, particularly in terms of moisture content and decay in the sapwood. Sapwood proportion was similar between living and dead trees, but the sapwood of dead trees contained more decay and had a lower moisture content than living trees. Mechanical properties and tracheid dimensions were 10% and 4% lower in dead trees than in living trees. We did not observe any major differences in wood properties between the three durations of defoliation, suggesting that wood degradation occurs before that. The study did not make it possible to determine the optimal duration of defoliation to harvest the stands.
by Marie-Claude Boileau | 14 November 2022
Published in Forestry: An International Journal of Forest Research, vol. 94(5): 611–629.
Manual aerial photo interpretation is used as a cost-effective source of data for forest inventories; however, the process of photo interpretation is inherently subjective and is often undertaken by multiple photo-interpreters for a given forest management area. In contrast, airborne laser scanning (ALS) data enable characterization of forest structures in a systematic fashion with quantifiable levels of accuracy and precision that often exceed required targets and standards. Yet, the gains associated with the use of new technologies for forest inventory are difficult to measure because the quality of existing photo-interpreted inventories have rarely been quantified.
Using ALS data as a reference, the objective of this study was to quantify the precision of photo-interpreted estimates of forest stand height and canopy cover (CC). We examined forest inventories from three study sites in three different forest regions of Canada. Each of the study sites was located within a different provincial jurisdiction with unique photo interpretation standards and forest ecosystems. Stand-level estimates of forest height and cover were compared to reference estimates generated from the ALS data. Overall, our results indicated that precision was greater for photo-interpreted estimates of height. While the relationship between photo-interpreted estimates of height and ALS estimates of height were generally linear and consistent for all study sites, relationships for CC were non-linear. Precision for both stand height and cover varied by dominant species, inventory stand structure, age and ALS canopy complexity. In most cases, the difference between the photo-interpreted estimate and the ALS estimate was statistically significant. Also, the variability in photointerpretation precision as a function of the aforementioned factors was not consistent among our three study sites, indicating that site-specific forest conditions and photo-interpretation procedures influence the precision of photo-interpreted estimates. The influence of local forest conditions and interpretation procedures are therefore important considerations to quantify the potential relative gains in precision, which may be afforded by technologies such as ALS for forest inventory programs.
by Marie-Claude Boileau | 14 November 2022
Paru dans Canadian Journal of Forest Research, vol. 4, p. 1750-1757.
A shadow fraction method was previously developed for mapping forest attributes of northern black spruce forests. This paper evaluates application of the method to (i) balsam fir stands, (ii) stands with higher volume and biomass than those of previous studies, and (iii) stands with a higher composition of deciduous trees and steeper slopes. Models developed for new test sites in central Labrador and western Newfoundland were not statistically different from previous models for biomass, volume, and basal area. Relative root-mean-square errors (RMSEr) for central Labrador were slightly lower than those found in other test sites (RMSEr = 24%–29%) but higher for western Newfoundland (RMSEr = 37%–43%), attributed to the higher upper limit of measured attributes and increased presence of deciduous trees. Results suggest that reasonable estimates can be generated for conifer forests of northeastern Canada; however, an alternative solution is needed where mixed and deciduous stands prevail. Measurement of ground plots over a wider range of species composition and forest structure is recommended for broader application to northern boreal forests and to further assess the potential role of the shadow fraction method in national-scale inventory programs.
