by Marie-Claude Boileau | 3 February 2021
Published in Forest Ecology and Management 476: 118460. https://doi.org/10.1016/j.foreco.2020.118460
In boreal forests where the fire return interval is long, the high structural variability of stands may affect wood traits. Here, we build on earlier work that revealed a difference in wood mechanical traits of black spruce between regular (regenerated from fire in the last 200 years) and irregular (undisturbed by fire for at least 200 years) stands. This study aimed to identify the ecological drivers of this variation in wood traits. To do so, we first sought to corroborate existing results on the effects of stand structure induced by the time since the last stand-replacing fire (TSLF) on wood mechanical stiffness in the eastern boreal forest of Canada. Results confirmed that black spruce from regular stands tend to produce wood with higher modulus of elasticity (MOE) than those from irregular stands. For both regular and irregular stands, we compared a set of linear models that were defined a priori to determine the structural and site productivity variables having the largest influence on MOE. The ‘growth efficiency index’ (aboveground woody biomass production per unit leaf area) was the best predictor of MOE variation among regular stands. For irregular stands, the model with TSLF as the sole explanatory variable was a better predictor of MOE than any other candidate model. However, we did not find strong evidence of a direct relationship between TSLF and wood traits, since our best models explained a relatively small proportion of the variance. Our results suggest that differences in wood traits could be attributable to the seed or layer origin of the trees and/or to the length of time trees remain in the understory. We propose that intensive wood production strategies focus on stands of the first post-fire cohort.
by Claire Morin | 2 February 2021
Published in Forest Ecology and Management 481: 118744. https://doi.org/10.1016/j.foreco.2020.118744
Over the last century, forest management has modified the natural disturbance regime of temperate and boreal forest regions. Consequently, this new disturbance regime may have profoundly affected the structure, composition and associated carbon stocks of forest ecosystems. The aim of this study is to document structural and compositional changes (1925–2015) in an actively managed forest region of eastern North America and their effects on above-ground biomass (AGB). We reconstructed stand structure, species composition and AGB of the preindustrial forest using 54,343 plots sampled by the Price Brothers & Company from 1924 to 1930. The present-day forest was described using 9561 plots surveyed during the most recent decadal forest inventories (1980s, 1990s, 2000s, 2010s) conducted by the Government of Quebec, eastern Canada. Between 1925 and 2015, the age structure shifted from a dominance of old-growth and mature stands (>80 years) to one of immature stands (<40 years) where early successional deciduous species increased in importance. The most striking difference was the sharp increase in stand density (>72%). Accordingly, tree diameter distribution changed markedly as a result of a strong increase of the smallest tree class to the expense of larger tree classes. Despite this structural reorganization, AGB has remained stable. Forest management history has induced a major forest structure reorganization. Aerial carbon stocks remain stable and resilient despite the strong density increase of small trees. The sharp increase in stand density could have significant impacts on biodiversity and resilience. In accordance with ecological forestry principles, the restoration of more natural forest conditions is expected to reduce the possible detrimental effects of forest management.
by Claire Morin | 2 February 2021
Published in SOIL ORGANISMS 92(3): 197–202. https://doi.org/10.25674/so92iss3pp197
Over the last decades, the application of calcitic materials to soil to restore the vigor of Sugar Maple (Acer saccharum Marsh) trees has increased in northeastern North America. However, few studies have evaluated how this treatment affects other ecosystem components, especially over several years. In Sugar Maple stands, the Eastern Red-backed Salamander (Plethodon cinereus Green, 1818) is one of the most abundant vertebrates and an important terrestrial species for key ecological processes. Because the species commonly serves as an indicator of forest disturbances, it is important to know how anthropogenic disturbances, such as soil liming, might affect it. The goal of this study was to evaluate the medium-term (5-year) effects of liming on body condition in a wild population of P. cinereus in Quebec, Canada. Lime (CaCO3) was spread by helicopter on a declining Sugar Maple forest growing on an acidic and base-poor soil. The results of this study, combined with those of previous published works, show that liming has no short- or medium-term effects on the body condition of the Eastern Red-backed Salamander. This study adds to those on other species in Europe and northeastern North America that report that liming has no major effect on amphibians when it is used as a treatment to restore acidified forest ecosystems. This should help foresters decide whether or not liming treatments are compatible with conservation, ecological, and management objectives.
by Marie-Claude Boileau | 2 February 2021
Published in Applied Geochemistry 125: 104860. https://doi.org/10.1016/j.apgeochem.2020.104860
How calcium (Ca) uptake by trees in eastern Canadian forests has responded to decades of atmospheric acid deposition and its sharp decrease that started three decades ago is still largely unknown. Here, we tested a novel approach based on the measurements of Ca and strontium (Sr) concentrations and Sr isotope signature (87Sr/86Sr ratio) in sequential extracts of sugar maple tree rings and soils to assess changes in Ca availability and sources through time. The study was conducted at three sites showing a gradient of one order of magnitude in soil mineral weathering fluxes and exchangeable pools of Ca. We found that wood Ca and Sr concentrations increased with Ca and Sr concentrations in the exchangeable fraction (NH4Cl extracts) of the top mineral soil across sites. In addition, wood 87Sr/86Sr ratio was strongly correlated with 87Sr/86Sr ratio of this soil fraction. Both Ca and Sr concentrations in the exchangeable fraction of the wood decreased from pith to bark at all sites, whereas no trend was observed for the wood residual fraction. This was interpreted as a result of radial mobility of Ca in sapwood rather than a decline in the uptake of Ca and Sr by tree roots over time. The 87Sr/86Sr ratio of tree rings slightly increased over time only at the site with the higher soil exchangeable Ca pool, suggesting an increase in the contribution of soil mineral weathering relative to atmospheric deposition. In contrast with our hypothesis, our results show i) no evidence of pronounced changes in the relative contribution of the atmospheric vs. soil mineral weathering Ca components over time at the site with the smallest soil exchangeable Ca pools; and ii) the difficulty of assessing the temporal changes in the availability and the sources of Ca from sequential extractions of the wood due to a dynamic exchange process of Sr (and therefore Ca) between the exchangeable and residual fractions of the wood.
by Marie-Claude Boileau | 2 February 2021
Published in Forest Ecology and Management 482: 118872. https://doi.org/10.1016/j.foreco.2020.118872
The demand for wood products continues to increase globally. Productivity of forest plantations can be greater than that of naturally regenerated forests. Plantation forestry could thus be employed to meet up to 75% of global wood supply by 2050. The resilience of natural forests could jeopardize plantation productivity. If the plantation scenario is not oriented in the same direction as the natural successional trajectories that are driven by resilience, then naturally regenerating tree species could recover to the detriment of planted species. Unproductive plantations will likely generate sustainability issues, as they must provide ecosystem services (e.g., wood fiber production) while being economically viable for forest management to be sustainable. Our general objective of our study was to assess whether resilience of natural forests can jeopardized plantation productivity. We studied successional trajectories in recent, young and old black spruce plantations that are located within the balsam fir ecological region on balsam fir ecological site types. To compare with a plantation scenario that was more susceptible to aiming in the same direction as resilience-driven successional trajectories, we also studied successional trajectories in recent, young and old black spruce plantations that are not only located within the balsam fir ecological region, but on black spruce ecological site types. Successional trajectories on balsam fir ecological site types pointed towards recovery of balsam fir and white birch, to the detriment of black spruce. Successional trajectories on black spruce ecological site types pointed towards the recovery of black spruce. Thus, we showed that resilience of natural forests could jeopardize plantation productivity when the plantation scenario is not oriented in the same direction as resilience-driven successional trajectories. It also can enhance plantation productivity when the regime is oriented in the same direction as resilience-driven successional trajectories. To ensure that plantations are economically viable and promote sustainability, forest managers should thus favor plantation scenarios that point in the same direction as resilience-driven successional trajectories. Finally, we suggest adopting such scenarios, and stress that it would also be necessary to develop regimes that would promote sustainability in the context of alternative successional trajectories that will undoubtedly arise because of global changes.
