by Claire Morin | 9 September 2022
Published in Annals of Forest Science 79(39). https://doi.org/10.1186/s13595-022-01152-w
Context: In temperate hardwood forests, increased intensity of soil and canopy disturbances tends to increase species richness due to the establishment of numerous early-successional plant species. However, while competitive pioneer species from early stages of succession can become recalcitrant and alter patterns of natural regeneration, very few studies have examined longer-term effects of these treatments on plant biodiversity.
Aims: In this study, we investigated mid-term (ca. 20 years) effects of different regeneration treatments with varying soil and canopy disturbance intensities. We compared understory plant communities in temperate hardwood forests from all the South of Quebec (Canada).
Methods: Using circular experimental plots of 1962.5 m2 (radius = 25 m), we measured taxonomic and functional diversity indices and soil properties using four levels of disturbance intensity in six temperate hardwood forests of Quebec distributed along a longitudinal gradient. Reference forests, i.e. control forests with no silvicultural treatment known for ≥ 80 years, were compared to 20-year-old single-tree selection cuts, group-selection cuts and group-selection cuts with soil scarification.
Results: Species richness in both group-selection treatments was higher than that in reference forests. Plant equitability and beta diversity among sites in both group-selection treatments were lower than in single-tree selection cuts and control forests. More intense treatments contributed to the mid-term persistence of recalcitrant competitor species (e.g. Rubus idaeus L., Prunus pensylvanica L.f.) whereas soil scarification appears to have negative sustained effects on species known to be sensitive to regeneration treatments (e.g. Monotropa uniflora L., Dryopteris spinulosa Kuhn).
Conclusions: In temperate hardwood forests of Southern Quebec, silvicultural treatments of higher intensities resulted in detrimental effects on soil properties, especially in the surface horizon, 20 years after disturbance. This legacy, in turn, affected the composition and diversity of understory plant communities. The more intense silvicultural treatments contributed to the persistence of pioneer species better adapted to a wider range of environmental conditions and resulted in a decrease in understory plant community heterogeneity among sites. Conversely, singletree selection cutting appeared to be the most appropriate silvicultural treatment for maintaining soil functions and heterogeneity of understory plant communities after 20 years; composition and structure being similar to long-undisturbed forests.
by Audrey Verreault | 25 August 2022
Published in Canadian Journal of Forest Research 52(8): 1186-1200. https://doi.org/10.1139/cjfr-2022-0073
The temperate mixedwood forests of eastern North America have been managed by partial cutting for several decades. To ensure that regeneration contributes to replacing the commercial-size stems that are removed by partial cutting, forest managers need to anticipate how saplings (i.e., regenerating trees with a diameter at breast height >1.0 cm) develop in terms of number and diameter. Using up to 20 years of monitoring data from three study sites, we developed a transition matrix model to predict the future number of saplings and their diameter distribution for mixed yellow birch (Betula alleghaniensis Britton) – conifer stands. Our results show that partial cutting allowed yellow birch, redmaple (Acer rubrum L.), red spruce (Picea rubens Sarg.), and balsam fir (Abies balsamea (L.) Mill.) saplings to reach merchantable size faster and in greater numbers than in untreated control plots.We also found that fewer hardwood saplings (yellow birch and red maple) than softwood saplings (red spruce and balsam fir) were required to produce 1 m2·ha−1 of merchantable basal area after 20–40 years. Finally, our model provides a tool for forest managers to predict sapling development in mixed hardwood and softwood stands over a full cutting cycle.
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.
