by Audrey Verreault | 1 February 2023
Published in Forests 14: 280. https://doi.org/10.3390/f14020280
Northern hardwoods are susceptible to a wide range of defects that can reduce the amount of sound wood with desirable qualities, such as the clear sapwood of sugar maple trees. Yet, the rate at which trees decline in quality due to the development of such defects has never been quantified in northern hardwood forests due to a dearth of repeat inventories that record the appearance of defects over time. As a result, it remains uncertain whether, and how, selection management reduces the probability of decline in quality. In this study, we quantify the rate at which trees decline in quality due to the development of defects, and we test several hypotheses regarding the influence of selection management on quality. Our results show that (1) the probability of decline in quality increases as trees grow larger; (2) crown dieback also increases the probability of decline in quality; (3) the probability of decline in quality is slightly lower in managed stands than in unmanaged stands, and (4) the probability of decline in quality increases with the mean annual temperature of the site. Finally, we combined our estimates of the probability of decline in quality with previous estimates of the probability of mortality to assess the overall risk associated with retaining trees of different species, sizes, and vigour profiles. The resulting metric can inform efforts to improve the management of northern hardwood forests by providing an integrated estimate of the risk that the value of a tree will be reduced, or eliminated, due to mortality or decline in quality.
by Audrey Verreault | 14 December 2022
Published in Forest Ecology and Management 529: 120720. https://doi.org/10.1016/j.foreco.2022.120720
Northern hardwood forests include many degraded stands dominated by trees of low vigour due to past management. To facilitate the implementation of stand improvement, several classification systems have been developed to help tree markers visually assess tree vigour at time of harvest based on the presence of individual defects. Because very few studies have tried to empirically validate such systems, it remains uncertain whether many of these defects should be used to guide the tree marking process. In this study, we assess tree vigour using repeated measurements collected as part of long-term silvicultural trials conducted in 615 permanent plots throughout the northern hardwood forest of Quebec, Canada. We aimed to determine whether the defects that are commonly used for classification have a significant effect on both growth and survival over three decades, using 9,338 sugar maple and 1,316 yellow birch trees. We also conducted a retrospective analysis to quantify the rate at which vigorous trees develop defects. Our results confirmed that crown dieback is by far the best indicator of vigour for both sugar maple and yellow birch trees. Conversely, our results revealed that stem defects did not contribute much to explaining the variation in vigour, except for the presence of cankers and fungi, which had modest effects. Consequently, stem defects should not be used as the main indicators of tree vigour, and existing classification systems should be simplified by reducing the number of stem defects under consideration for this purpose. Lastly, our results showed that the rate that vigorous trees develop defects increased with increasing diameter, more so than the probability of surviving. Thus, assessing the risk of retaining large trees should not only be based on survival, but also on the risk of developing defects that reduce the growth and value of trees.
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.
