by Claire Morin | 24 August 2022
Published in Frontiers in Plant Science 13(920852). https://doi.org/10.3389/fpls.2022.920852
Global warming is predicted to extend the growing season of trees and plants, and advance spring phenology. However, intensification of extreme climate events in midlatitude forests, from weakening of the jet stream and atmospheric blockings, may expose trees to increased risk associated with more frequent late-spring frosts. Still, little is known regarding the intraspecific variation in frost tolerance and how it may be shaped by local adaptation to the climate of seed origin. As part of an assisted migration trial located in different bioclimatic zones in the province of Quebec, Canada, and following an extensive late-spring frost that occurred at the end of May 2021, we evaluated the frost damages on various white spruce (Picea glauca) seed sources tested on three sites (south, central, and north). The severity of frost damages was assessed on 5,376 trees after the cold spell and an early spring warming which advanced bud flush by approximately 10 days on average. The frost damage rate was similar among sites and seed sources and averaged 99.8%. Frost damage severity was unrelated to the latitude of seed origin but was variable among sites. The proportion of severely damaged trees was higher in the northern site, followed by central and southern sites. The proportion of severely damaged trees was linearly and inversely related to tree height before the frost event. Apical growth cancelation was not significantly different among seed sources including local ones, and averaged 74, 46, and 22%, respectively, in central, northern, and southern plantation sites. This study provides recommendations to limit the loss of plantation productivity associated with such a succession of spring climate anomalies. Implications for seed transfer models in the context of climate change and productivity of spruce plantations are discussed in the light of lack of local adaptation to such pronounced climate instability and ensuing large-scale maladaptation.
by Audrey Verreault | 24 August 2022
Published in Frontiers in Forests and Global Change 5(818474). https://doi.org/10.3389/ffgc.2022.818474
Sustainable management of forest ecosystems requires the use of reliable and easy to implement biodiversity and naturalness indicators. Tree-relatedmicrohabitats (TreMs) can fulfill these roles as they harbor specialized species that directly or indirectly depend on them, and are generally more abundant and diverse in natural forests or forests unmanaged for several decades. The TreM concept is however still recent, implying the
existence of many knowledge gaps that can challenge its robustness and applicability. To evaluate the current state of knowledge on TreMs, we conducted a systematic review followed by a bibliometric analysis of the literature identified. A total of 101 articles constituted the final corpus. Most of the articles (60.3%) were published in 2017 or after. TreM research presented a marked lack of geographical representativity, as the vast majority (68.3%) of the articles studied French, German or Italian forests. The main themes addressed by the literature were the value of TreMs as biodiversity indicators, the impact of forest management on TreMs and the factors at the tree- and stand-scales favoring TreMs occurrence. Old-growth and unmanaged forests played a key role as a “natural” forest reference for these previous themes, as TreMs were often much more abundant and diverse compared to managed forests. Arthropods were the main phylum studied for the theme of TreMs as biodiversity indicators. Other more diverse themes were identified, such as restoration, remote sensing, climate change and economy and there was a lack of research related to the social sciences. Overall, current research on TreMs has focused on assessing its robustness as an indicator of biodiversity and
naturalness at the stand scale. The important geographical gap identified underscores the importance of expanding the use of the TreMs in other forest ecosystems of the world. The notable efforts made in recent years to standardize TreM studies are an important step in this direction. The novelty of the TreM concept can partially explain the thematic knowledge gaps. Our results nevertheless stress the high potential of TreMs for
multidisciplinary research, and we discuss the benefits of expanding the use of TreMs on a larger spatial scale.
by Claire Morin | 24 August 2022
Published in Forest Ecology and Management 512: 120139. https://doi.org/10.1016/j.foreco.2022.120139
Northern hardwoods are an economically, ecologically, and culturally important forest type spanning the upper latitudes of the United States and the lower latitudes of Canada. The prevalence and value of these forests have driven silviculture research for over a century. During this time, silvicultural approaches have varied widely, searching for scenarios to meet traditional commodity-based and diversifying ecological forestry objectives. To better understand this forest type and the spectrum of appropriate silvicultural options, we analyzed regional inventory data from the United States and Canada and synthesized decades of scientific studies. Calculated overstory tree (stems ≥ 12.5 cm diameter at breast height) metrics show common structural conditions across mature northern hardwood forests and dominance of sugar maple (Acer saccharum). However, density and composition metrics for established reproduction (saplings 2.5 to 12 cm dbh) emphasize challenges for establishing and maintaining economically and ecologically valued trees species broadly and regionally. Our work underscores the variation in northern hardwoods within and across its distribution, driven by characteristics like disturbance regimes, land use history, and ownership patterns. We conclude maintaining this important forest type amid climate uncertainty and associated effects, like proliferation of exotic insects and diseases, requires recalibration of historically applied silvicultural systems and application of emerging tools.
by Svetlana Savin | 24 August 2022
Published in Forest Ecology and Management 511: 120142. https://doi.org/10.1016/j.foreco.2022.120142
In northern hardwood stands of the northeastern USA and southeastern Canada, the abundance and occurrence of American beech (Fagus grandifolia Ehrh) regeneration have increased substantially over the past decades, to the detriment of other deciduous species such as sugar maple (Acer saccharum Marshall) and yellow birch (Betula alleghaniensis Britton). To promote the regeneration of these declining species, we established an experimental study near Qu´ebec City (Quebec, Canada) to compare the effects of various partial cutting treatments and mechanical control of understory American beech. The design comprises 4 randomized complete blocks, each containing an uncut control, a hybrid single-tree and group selection cutting (SC), two intensities of continuous cover irregular shelterwood (CCIS) and an extended irregular shelterwood (EIS). American beech regeneration, which dominated the sapling layer before cutting, was removed with brush saws in gaps created in the SC and CCIS treatments as well as in the entire understory of the EIS treatment. In addition, gaps and the EIS understory were scarified to favor yellow birch regeneration, and 12 exclosures were built to prevent cervid browsing in CCIS gaps and in entire understory of the EIS treatment. Ten years after cutting, yellow birch regeneration was more abundant in gaps and in the EIS treatment than in the uncut control. These results confirm that increasing the understory light level, eliminating American beech saplings and scarifying the soil can successfully favor yellow birch establishment. However, preferential browsing of yellow birch outside exclosures maintained the overall dominance of American beech in the long term. Thus, under these conditions, damage from repetitive browsing outweighed the positive effects of actions aimed at promoting the regeneration of yellow birch. In the end, despite abundant seed availability, sugar maple remained only a minor component of the regeneration
by Claire Morin | 24 August 2022
Published in Frontiers in Forests and Global Change 5: 879382. https://doi.org/10.3389/ffgc.2022.879382
Under climate change, drought conditions are projected to intensify and soil water stress is identified as one of the primary drivers of the decline of forests. While there is strong evidence of such megadisturbance in semi-arid regions, large uncertainties remain in North American temperate forests and fine-scale assessments of future soil water stress are needed to guide adaptation decisions. The objectives of this study were to (i) assess the impact of climate change on the severity and duration of soil water stress in a temperate forest of eastern North America and (ii) identify environmental factors driving the spatial variability of soil water stress levels. We modeled current and future soil moisture at a 1 km resolution with the Canadian Land Surface Scheme (CLASS). Despite a slight increase in precipitation during the growing season, the severity (95th percentile of absolute soil water potential) and duration (number of days where absolute soil water potential is greater than or equal to 9,000 hPa) of soil water stress were projected to increase on average by 1,680 hPa and 6.7 days in 80 years under RCP8.5, which correspond to a 33 and 158% increase compared to current levels. The largest increase in severity was projected to occur in areas currently experiencing short periods of soil water stress, while the largest increase in duration is rather likely to occur in areas already experiencing prolonged periods of soil water stress. Soil depth and, to a lesser extent, soil texture, were identified as the main controls of the spatial variability of projected changes in the severity and duration of soil water stress. Overall, these results highlight the need to disentangle impacts associated with an increase in the severity vs. in the duration of soil water stress to guide the management of temperate forests under climate change.
