Young plantation trees are often highly vulnerable to insect herbivory in ways that are difficult to predict as underlying mechanisms linked to plant traits and natural enemy pressure interact in context-dependent ways. We compared bottom-up and top-down forces acting on spruce budworm (Choristoneura fumiferana) on young white spruce (Picea glauca) trees in plantations vs in natural regeneration under hardwood canopy. The spruce budworm is the most important outbreaking conifer defoliator in Eastern Canada, and we aim to better understand budworm herbivory on young trees, given its importance for post-outbreak forest succession. We conducted a 4-year field survey in Northwestern Québec, Canada, to compare plant phenology, budworm density, defoliation rates, predator populations, and parasitism between the two habitats. We also designed manipulative experiments with sentinel larvae to assess bottom-up and top-down forces in these habitats. The field survey showed earlier budburst phenology in plantation trees, affecting synchronization with budworm emergence from diapause. Field survey results also included slightly higher budworm density and lower larval parasitism in plantations, but no significant difference in current-year growth defoliation. The bottom-up experiment showed slightly better budworm biological performance, indicated by higher pupal mass, in plantations. The top-down experiment suggested slightly higher predation and parasitism in the natural forests. Together, our results show how mechanisms controlling insect defoliator populations are context-dependent. In plantations both bottom-up and top-down pressures on the spruce budworm appear slightly eased, leading to marginally better biological performance and higher population density of this forest pest. However, differences are so minor that no impact on defoliation is observed.

Windthrow is a natural disturbance affecting forest dynamics, characterized by tree uprooting or stem breakage when wind forces surpass tree anchorage strength or stem resistance. Windthrow mortality has been related to several ecological biotic and abiotic factors. However, the influence of natural root grafting on windthrow mortality remains unknown. This research evaluated the influence of root grafting on windthrow mortality by excavating root systems of jack pine (Pinus banksiana) in four windthrow-affected riparian buffers and analyzing root grafts using a dendrochronological approach. Our results revealed that natural root grafting decreased the uprooting likelihood but increased the propensity for stem breakage. In addition, root grafting occurred more frequently in trees closer to one another. These results suggest that root grafting influences the windthrow mortality type, with tree proximity being a good predictor for root grafting. This study provides valuable insights into windthrow dynamics, particularly relevant for managing windthrow mortality following partial harvesting and riparian buffers, conserving soil, and mitigating the impacts of windthrow events in the face of climate change.

There are ongoing debates among different stakeholders about which forest and ungulate management strategies will sustain high levels of timber and animal harvest and maintain important ecosystem functions under climate change. Ungulate-forest interactions are complex, including periods where forest regeneration is sensitive to browsing pressure, making it difficult to predict the consequences of a given strategy over time. To aid decision-making, we simulated the impacts of moose browsing on forest succession under 18 different combinations of moose (Alces alces) harvest rate levels and forest management scenarios in a boreal forest landscape in southern Sweden given projected changes in forest growth due to climate change. We found that the current management practices are important for sustaining a moose-forest system. Increasing moose harvest rates led to slightly smaller moose populations, larger estimates of landscape carrying capacity, and less biomass removal of Scots pine (Pinus sylvestris), a commercially valuable species. However, minor changes in the moose harvest were hardly affecting timber production. Increasing the timber harvest rotation time led to the highest estimates of Scots pine biomass, while thinning younger cohorts lead to the highest estimates of Norway spruce (Picea abies) biomass. These changes came without much effect to moose population dynamics. However, the increased broadleaf production scenario had a very large positive effect on total aboveground live biomass of deciduous species and on landscape carrying capacity and moose density. This scenario subsequently resulted in the greatest estimates of biomass removal of Scots pine, highlighting the tradeoffs associated with increased moose production.

In Canada, clearcutting is the most widely used silvicultural system in boreal forests despite potential impacts on forest simplification and biodiversity loss. Retaining mature trees is suggested to maintain stand structure and biodiversity, especially for promoting the regeneration of shade-tolerant species. Partial harvesting is considered a promising alternative to the clearcutting system as a means of integrating ecological, economic, and social objectives into silvicultural planning; however, this approach must be developed for use in natural boreal forests. Here, we evaluate the effects of silvicultural treatments on natural regeneration in stands of natural even-aged mature black spruce (Picea mariana (Mill.) B.S.P.), 18 years after cutting. In 2003, in the Saguenay and North Shore regions of Quebec, an experimental design of fully randomized blocks was established across six sites, each containing two forest stand types (younger and older stands) and six silvicultural treatments. In 1 512 microplots, we categorized all tree seedlings by species and height class and assessed a dominant seedling for growth-related variables, and microenvironment. We found that 18 years after treatment, mini-strip shelterwood harvesting produced the highest black spruce seedling density (39 765 seedlings/ha). In contrast, clearcutting produced a seedling density that was three times lower than uniform shelterwood harvesting but demonstrated a twofold increase in seedling terminal shoot length growth. Mineral soil, spot scarification, moss cover with Polytrichum spp., and distance from residual strips positively correlated with black spruce seedling density. Our study highlights the potential of shelterwood systems as a silvicultural alternative to clearcutting for promoting black spruce regeneration in Canadian boreal forests.

Despite the wide application of riparian buffers in the managed boreal forest, their long-term effectiveness as freshwater protection tools remains unknown. Here, we evaluate windthrow incidence in riparian buffers in the eastern Canadian boreal forest and determine the effect of windthrow on the water quality index of the adjacent freshwater ecosystems. We studied 40 sites—20 riparian buffers, aged 10 to 20 years after harvesting and 20 control sites within intact riparian environments—distributed among clay and sandy (esker) soils and black spruce (Picea mariana) and jack pine (Pinus banksiana) stands. We observed more windthrow in the harvested stands (36%) relative to the control sites (16%), regardless of substrate and species. We determined that the most important factors explaining windthrow were exposition, harvesting, aquatic environment size, and stand characteristics. These factors drive wind exposure, speed, and force, which determine post-harvest windthrow risk. Furthermore, windthrow negatively affected the water quality index of the adjacent aquatic systems, i.e., greater windthrow decreased the protective effect of the riparian buffer. We recommend increasing the use of partial harvest near riparian environments and adapting riparian buffers to site conditions to ensure the long-term protection of adjacent freshwater ecosystems.

Partial cutting has lower canopy removal intensities than clearcutting and has been proposed as an alternative harvesting approach to enhance ecosystem services, including carbon sequestration and storage. However, the ideal partial cutting/clearcutting proportion that should be applied to managed areas of the eastern Canadian boreal forest to enhance long-term carbon sequestration and storage at the landscape scale remains uncertain. Our study projected carbon dynamics over 100 years (2010–2110) under a portfolio of management strategies and future climate scenarios within three boreal forest management units in Quebec, Canada, distributed along an east–west gradient. To model future carbon dynamics, we used LANDIS-II, its Forest Carbon Succession extension, and several extensions that account for natural disturbances in the boreal forest (wind, fire, spruce budworm). We simulated the effects of several management strategies on carbon dynamics, including a business-as-usual strategy (clearcutting applied to more than 95 % of the annually managed area), and compared these projections against a no-harvest natural dynamics scenario. We projected an overall increase in total ecosystem carbon storage, mostly because of increased productivity and broadleaf presence under limited climate change. The drier Western region under climate scenario RCP8.5 was an exception, as stocks decreased after 2090 because of the direct negative effects of extreme climate change on coniferous species’ productivity. Under the natural dynamic scenario, our simulations suggest that the Quebec Forest in the Central and Western regions may act as a carbon sink, despite high fire-related carbon emissions, particularly under RCP4.5 and RCP8.5 Conversely, the eastern region periodically switched from carbon sink to source following SBW outbreaks, thus being a weak sink over the simulation period. Applying partial cutting to over 50 % of the managed forest area effectively mitigated the negative impacts of climate change on carbon balance, reducing differences in stand composition and carbon storage between naturally dynamic forests and those managed for timber. In contrast, clearcutting-based scenarios, including the business-as-usual approach, substantially reduced total ecosystem carbon storage— by approximately double (10 tC ha−1 yr−1) compared to partial cutting scenarios (<5 tC ha−1 yr−1). Clearcutting led to higher heterotrophic respiration due to the proliferation of fast-decomposing broadleaves, resulting in lower carbon accumulation compared to partial cuts. Our findings underscore the importance of balancing canopy removal intensities to increase carbon sequestration and storage while preserving other ecosystem qualities under climate change.

Nitrogen is an essential nutrient for plant functioning, photosynthesis, and metabolic activities. In terrestrial settings, nitrogen is not always sufficiently available because its basic form (N2) must be fixed into other forms, such as nitrate and ammonium, to be usable by plants. Adding nitrogenous fertilizer to soils may provide a means of increasing forest productivity. Ammoniacal nitrogen (N-NH3), an effluent produced during gold extraction, requires mining companies to manage its long-distance and costly transportation offsite for disposal. Applying this nitrogenous effluent, in its treated form of ammonium sulfate (ammoniacal nitrogen from mine water was converted into ammonium sulfate locally), to regional forest stands could provide a cost-effective and more environmentally sound means of managing this waste product and enhance forest productivity. Here, we conducted greenhouse- and field-based experiments to evaluate ammonium sulfate fertilization on black spruce (Picea mariana) and jack pine (Pinus banksiana) seedling growth. We assigned five treatments, varying in terms of the fertilizer concentration and presence/absence of biochar, to seedlings in greenhouse trials. We also applied various concentrations of ammonium sulfate to an 8-year-old black spruce plantation in Abitibi-Témiscamingue, Québec. We found that black spruce and jack pine seedlings experienced greater growth than the controls in terms of the stem diameter (32–44%), seedling height (21–49%), and biomass (86–154%). In the field experiment, we observed 37% greater volumetric growth in plots receiving medium-level fertilization than the control. Although nitrogen fertilization lowered the soil pH, essential nutrients increased to favor greater seedling growth. Thus, ammonium sulfate, derived from local mining effluent, appears to offer a suitable alternative for enriching nitrogen-limited boreal soils and increasing tree growth. This application could benefit both regional mining industries and forest management bodies.

Extreme weather events are expected to increase in frequency and intensity in South America, likely causing decreased plant productivity and altering species distributions. Yerba mate (Ilex paraguariensis) is a tree species native to South America and has an ecological, social, and economic importance in several countries. Natural forests and cultivated areas of yerba mate will be endangered by climate change because of the expected reduction in water availability. Here we determined how clonal genotypes of yerba mate (BRS BLD Yari, BRS BLD Aupaba, BRS 408, and EC40) respond to four levels of soil water holding capacity (100%, 80%, 60%, and 40% WHC) over 60 days, by evaluating the plants’ morphophysiological and biochemical characteristics. We observed a reduction in plant height and biomass accumulation related to the decrease in water availability; physiological and biochemical parameters indicated that water-deficit stress reduced the plants’ C assimilation and increased their production of bioactive compounds. BRS BLD Yari had a higher tolerance to low water availability, with greater biomass accumulation and photosynthetic rates that indicate greater water use efficiency. Understanding how different yerba mate genotypes respond to water deficit is essential for species conservation and developing climate-adapted breeding programs.