Steve Bédard

Beech bark disease is a major concern for northern hardwood forest management that affects most of the American beech range in North America. In infected stands, mitigating effects of the disease and promoting more resistant beech populations for natural regeneration relies heavily on our ability to identify high-risk trees and adapt tree marking for partial harvesting. We monitored several individual characteristics, including external signs of disease, on 871 beech trees in recently infected northern hardwood stands at the northern range limit of American beech in Canada, to assess their ability to predict mortality over an 8-year period. At the stand level, the mortality rate over the study period was 29.3%, while the uninfected rate was 16.6%. At the tree level, the diameter, the levels of Neonectria perithecia coverage on the stem, crown dieback, and the level of canker coverage on the bark had the greatest capacity to predict individual short-term mortality. Therefore, tree markers should first select trees with a diameter > 20 cm that are affected by any sign or symptom of the disease, followed by smaller trees with >10% coverage of Neonectria perithecia or crown dieback >25%, and lastly, trees with >50% coverage of canker.

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.

Multi-cohort forest management in northern hardwood stands may well be the best way to successfully regenerate tree species of intermediate shade tolerance, such as yellow birch (Betula alleghaniensis Britt.). The creation of large enough gaps in the canopy favors increased light availability within the opening, while soil scarification provides suitable germination seedbeds. Evidence of these methods’ success nonetheless remains mostly the purview of experimental studies rather than operational tests. In Quebec, Canada, the multi-cohort methods promoted include group selection cutting and patch cutting. The present study tested their implementation at an operational scale and over a large territory in both hardwood-dominated and mixedwood stands. We assessed their efficacy in promoting natural regeneration of commercial hardwood trees, notably yellow birch and sugar maple (Acer saccharum Marsh.). We conducted regeneration surveys at 2, 5, 10, and 15 years after harvest. Overall, group selection and patch cuttings were successful in regenerating the target species. Yellow birch, for instance, showed a mean stocking around 60% and a mean sapling density around 3400 stems ha⁻¹ after 15 years. We compared several variables for measuring regeneration in early years, and found that the relative abundance, the stocking based on one stem per sampling unit, and the mean maximum height were good predictors of the relative presence of yellow birch and sugar maple in 15-year-old canopy openings. Using smaller sampling units (6.25 m² rather than 25 m²) and waiting until year 5 may be more useful for making such predictions. In addition, there was an important turnover in vertical dominance in these openings. Non-commercial woody competitors were frequently dominant in early years but were often replaced by commercial hardwoods, notably yellow birch. We propose certain thresholds for assessing the success of post-harvest regeneration and for evaluating the need for a cleaning treatment.

The management of sugar maple (Acer saccharum) at the northern edge of its range is mainly oriented toward timber production, from trees of higher grades. However, both the quality of mature trees in natural stands and how the quality may vary depending on the silvicultural treatment are unknown, especially under northern conditions. The objective of this study was to describe the variation in stem quality of mature maple trees (diameter >33 cm) according to climatic, geographic or soil variables, and to evaluate the effects of a first selection cutting cycle on this quality. Annual temperature (1.7–4.1° C) was the most important variable explaining differences in the proportion of higher-grade trees, with a 16 percent gain associated with every additional increase in degrees Celsius. The practice of a first selection cutting was associated with an 11 percent gain in this proportion. Although the actual proportion of high-quality trees was below 35 percent on the coolest sites, a proper tree selection through silviculture could likely improve this proportion in future decades, whereas the potential effects of climate change are unclear.

We used 11 silvicultural trials in forests dominated by sugar maple (Acer saccharum Marsh.) to compare the development of structural attributes between unmanaged stands and stands subjected to two selection cuttings. Results showed that managed stands had significantly lower amounts of large live and dead trees, lower downed coarse woody debris (CWD) volume and lower density of large trees with wildlife cavities compared to unmanaged stands. Despite these differences, both managed and unmanaged stands had sufficient amounts of large trees and large trees with wildlife cavities to maintain excavator bird habitat based on minimum target guidelines from the literature. In both managed and unmanaged stands, minimum target guidelines to emulate old-growth conditions were not met: at least 30 live trees ha⁻¹ >49.0 cm in diameter at breast height, and at least 11 m³ ha⁻¹ of downed CWD volume with large-end diameter >44.0 cm. We discuss management options to promote the development of structural attributes in managed, uneven-aged sugar maple stands.

Many northern hardwood stands include several low-vigor trees as a result of past management. To restore these degraded stands, partial cuts are applied with partly validated tree classification systems that are based upon apparent stem defects. We sampled 214 sugar maple (Acer saccharum Marsh.) and 84 yellow birch (Betula alleghaniensis Britt.) trees from six sites covering the northern hardwood forest zone of the Province of Quebec, Canada. We evaluated their vigor with a four-class system, and quantified the growth efficiency index and several indices that were based solely upon radial growth. The growth efficiency index increased non-significantly with increasing tree vigor class. The five-year basal area increment (BAI_-1-5) was significantly different between the lowest and highest tree vigor classes. Yet, temporal changes in BAI_-1-5 helped classify correctly only 16% of high-vigor trees that became poorly vigorous 8–10 years later. Overall, these results suggest that the tree classification system is weakly related to actual tree vigor and its application likely generates few significant gains in future stand vigor. Modifying and simplifying the tree vigor system must be considered to facilitate the tree marking process that is required to improve the vigor of degraded stands.