Martin-Michel Gauthier

Climate change is forcing us to reassess the foundational principles of forest management. Shifts in temperature, precipitation, and extreme weather events are altering both our understanding of forest ecosystems and how we steward them. Scientific research aimed at providing useful information can help forest managers make informed, evidence‐based decisions. For example, black cherry's ( Prunus serotina Ehrh.) distribution in eastern Canada represents the northern limit of its native range, where it is thought to have the potential to become a commercial tree species in the future. We documented the long‐term (1967–2022) radial increment of 1405 growth observations from 787 trees distributed among 260 ground plots in eastern Canada using the Multi‐Agency Ground Plot (MAGPlot) database. Out of several models assessed, including variables related to climate, physiography, and competition, the competition model had the best fit in absolute and relative radial growth. Increases in total basal area of the plot lowered black cherry's radial growth. Similarly, absolute and relative radial growth were much higher among dominant and codominant trees compared to intermediate and suppressed trees, but growth differences became less pronounced over time. The temporal decrease in growth likely coincided with reductions in anthropogenetic nitrogen deposition. The absence of strong climate–growth relationships in the MAGPlot database should not imply that black cherry is unaffected by climate. Rather, our findings underscore the difficulty of detecting these effects with inventory data. Implications related to forest management reside in the importance of managing the amount of competition to maintain trees in dominant or codominant positions and sustain tree growth.

Six decades of temporal changes in the abundance of sugar maple (Acer saccharum Marsh.) were investigated using a network of multi‐agency ground plots (MAGPlots) located across Ontario, Québec, and New Brunswick, Canada. Based on a composite dataset of nearly 400 plots mainly composed of sugar maple trees (≥ 50% basal area, m² ha⁻¹), results showed that the relative abundance (% total sapling basal area) of sugar maple saplings declined significantly over time. On average, the relative abundance of sugar maple saplings decreased significantly between 1970 and 2022. Out of a wide range of potential explanatory variables, including stand conditions, harvest intensity (0%–92% basal area removal), regional ecozones, and climate variables, the relative abundance of American beech (Fagus grandifolia Ehrh.) saplings was the only variable that had a negative effect on the relative abundance of sugar maple saplings. The plot‐specific distribution of change between the final and initial measurements over time revealed that many plots showing a decline in relative sugar maple sapling abundance also experienced an increase in relative American beech sapling abundance. The lack of differences between harvested and unharvested plots suggests that beech sapling control in the understory and soil liming treatments may be required to help promote sugar maple regeneration and development.

The influence of water deficits and drought on tree physiological processes, growth, and survival has been the focus of substantial research efforts and debate over the past decades, but there is still a need to quantitatively link finer scale mechanistic explanations of the influence of water status with the physiological responses of trees, particularly for those past the sapling stage. Hence, the objective of this study was to link accumulated water stress during the growing season to leaf physiological response mechanisms of Juglans nigra L. trees. Results showed that trees subjected to higher cumulative water stress had lower maximum light-saturated photosynthesis (A_max), initiated net photosynthesis at higher light levels (I_c), and displayed reduced effectiveness of CO₂ fixation per photons absorbed (Q_e) at the bottom and upper positions along the vertical canopy gradient. Results suggest that water stress integral (S_ψ), a variable that takes into account accumulated water deficits, would be useful to help future research efforts aimed at investigating responses to drought in trees past the sapling stage.

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.

Lack of available workforce in motor-manual operations has led to increased interest in mechanized precommercial thinning (PCT) treatments. We evaluated 15 years of growth and yield development of a very dense (27,000 stems ha^–1) balsam fir (Abies balsamea (L.) Mill) and black spruce (Picea mariana (Mill.) B.S.P.) stand after six PCT treatments: (1) motor-manual (MAN), (2) motor-manual with crop tree release (MAN-C), (3) mechanized (MEC), (4) mechanized with residual patches (MEC-P), (5) semi-mechanized (mechanized followed by motor-manual, MEC-S), and (6) unthinned control (CON). Compared to CON, both MAN and MEC-S increased height of balsam fir study trees by 53–56% and diameter at breast height (DBH) by 57–58%. MAN-C and MEC-S increased DBH of black spruce study trees by 15–31% over all other treatments. The proportion of merchantable basal area (BA) was higher in MAN (62%) and MEC-S (56%) than in CON (22%) and MEC (25%), without a reduction in total BA. PCT treatments that provided a uniform distribution of potential crop trees (MAN, MEC-S) performed better than MAN-C and MEC-P, while MEC yielded the poorest responses. Our findings highlight the need to develop new tailored mechanized systems for high wood production and low operational cost.

We used a permanent sample plot network established to monitor the effects of forest management practiced in mature northern hardwood and mixedwood stands in Québec, Canada to address two important questions related to tree mortality: (1) How does partial cutting affect tree mortality? (2) Which variables best explain tree mortality by different modes of death (standing death, uprooting or stem breakage)? Decennial tree deaths were lower after partial cutting than in unharvested plots, but the annual proportion of tree death was similar (1.25%·year^-1). At the tree level, a risk-product classification demonstrated the strongest evidence on influencing total mortality, followed by species, the presence of a logging injury, and tree size. Annual temperature was the only climatic variable explaining variations in total risk of tree mortality, and always among the first three variables explaining differences among the three modes of death. The risk of standing death also increased with increasing annual precipitation, while the risk of stem breakage and, to a lesser extent, of being uprooted, decreased with increasing precipitation. Additionally, we found strong evidence to support the effect of the potassium/magnesium ratio of the humus layer on the risk of being uprooted. This information is critical to better understand tree mortality processes.