by Audrey Verreault | 17 January 2024
Published in Biogeosciences 20(24): 5087-5108. https://doi.org/10.5194/bg-20-5087-2023
The carbon cycle in Arctic–boreal regions (ABRs) is an important component of the planetary carbon balance, with growing concerns about the consequences of ABR warming for the global climate system. The greatest uncertainty in annual carbon dioxide (CO2) budgets exists during winter, primarily due to challenges with data availability and limited spatial coverage in measurements. The goal of this study was to determine the main environmental controls of winter CO2 fluxes in ABRs over a latitudinal gradient (45∘ to 69∘ N) featuring four different ecosystem types: closed-crown coniferous boreal forest, open-crown coniferous boreal forest, erect-shrub tundra, and prostrate-shrub tundra. CO2 fluxes calculated using a snowpack diffusion gradient method (n=560) ranged from 0 to 1.05 g C m2 d−1. To assess the dominant environmental controls governing CO2 fluxes, a random forest machine learning approach was used. We identified soil temperature as the main control of winter CO2 fluxes with 68 % of relative model importance, except when soil liquid water occurred during 0 ∘C curtain conditions (i.e., Tsoil≈0 ∘C and liquid water coexist with ice in soil pores). Under zero-curtain conditions, liquid water content became the main control of CO2 fluxes with 87 % of relative model importance. We observed exponential regressions between CO2 fluxes and soil temperature in fully frozen soils (RMSE=0.024 ; 70.3 % of mean ) and soils around the freezing point (RMSE=0.286 ; 112.4 % of mean ). increases more rapidly with Tsoil around the freezing point than at Tsoil<5 ∘C. In zero-curtain conditions, the strongest regression was found with soil liquid water content (RMSE=0.137 ; 49.1 % of mean ). This study shows the role of several variables in the spatio-temporal variability in CO2 fluxes in ABRs during winter and highlights that the complex vegetation–snow–soil interactions in northern environments must be considered when studying what drives the spatial variability in soil carbon emissions during winter.
by Audrey Verreault | 7 December 2023
Published in ZooKeys 927: 153-154. https://doi.org/10.3897/zookeys.927.52153
In a paper about the biodiversity of Microgastrinae (Hymenoptera: Braconidae) in Ottawa Canada (Fernandez-Triana et al. 2016) some figure captions are incorrect. That includes three cases where the species name shown does not correspond with the actual species being depicted in those figures. To correct those mistakes, we detail below the correct captions for the corresponding figures.
by Audrey Verreault | 4 December 2023
Published in Forest Ecology and Management 553: 121600. https://doi.org/10.1016/j.foreco.2023.121600
Soil scarification is a common soil mechanical preparation (MSP) method in forestry aimed to enhance the success of reforestation. However, by turning over and displacing the humus (forming a mound; M), and producing furrows of bare mineral soil (F), it is believed that this method has a substantial effect on soil C stocks. Here, we assessed the influence of this MSP on soil C stocks in two boreal lichen woodlands (LWs) in Québec, Canada, scarified ten and two years before sampling (2012 and 2020 sites, respectively). Carbon stocks averaged 11.8–15.4 kg C m−2 in the undisturbed section of the LWs (IF) with 9–15 % located in the vegetation, 36–42 % in the humus and 42–55 % in the mineral soil (0–30 cm). MSP caused a C concentration decline of ∼105 g C kg−1 in the displaced humus. Unexpectedly, this decrease was similar at both sites, suggesting that most C losses from this horizon occurred within two years. Higher C stock in the mineral horizons of the M than of the IF compartment at the 2012 site, suggests that a fraction of the C lost from the displaced humus may not have been released to the atmosphere but rather translocated to the underlying mineral soil. However, no such phenomenon was detected at the 2020 site, where a net C loss from the mineral soil was observed. Overall, the use of mass balance equations did not show evidence of net C losses at the scale of the whole profile in the disturbed sections of both LWs following MSP. This was partly due to site heterogeneity and a sampling bias, but also to mechanisms such as C translocation from the organic to the mineral soil horizons, and the replenishment of the soil C pool owing to natural regeneration occurring at the surface of the furrows. Overall, this study suggests that MSP may not have as strong an impact on soil C stocks as previously believed. Additionally, it highlights the challenges associated with estimating C changes in the soil following MSP and discusses ways to improve the assessment of C dynamics in such heterogeneous habitats.
by Audrey Verreault | 17 November 2023
Published in Forest Ecology and Management 552(2024): 121584. https://doi.org/10.1016/j.foreco.2023.121584
Regeneration failures in the closed-crown boreal forest, which lead to the creation of open lichen woodlands, are expected to increase with climate change due to a rise in burn rates. Past studies have shown that it was possible to restore the productivity of those stands through planting. Since most lichen woodland stands are remotely located, afforestation through planting can be prohibitive. Therefore, the objective of this research was to measure the afforestation efficiency of lichen woodlands through scarification and natural seeding after clear-cutting. Our results showed that clear-cutting, when combined with scarification, promoted seedling establishment more strongly than clear-cutting alone. Scarification was also necessary for creating suitable microsites for germination, which were essentially bare mineral soil and decomposed organic matter. Last, seedling growth was higher in lichen woodlands when logging and scarification were combined, but lower than their counterpart feather moss stands. We conclude that afforestation of lichen woodlands in the closed-crown boreal forest is possible through natural seeding following scarification and could be a cost-effective option compared to planting.
by Audrey Verreault | 23 October 2023
Published in Tree Genetics & Genomes 19(49). https://doi.org/10.1007/s11295-023-01625-7
Genetic parameters for growth, trunk quality, and susceptibility to frost and Sphaerulina musiva attack were estimated from 34 half-sib families of hybrid poplar from the crossing of non-native parents, Populus maximowiczii A. Henry, and Populus trichocarpa Torr. & Gray, 3 and 6 years after planting. The use of spatial analysis proved to be the best method for quantitative growth data. The proportion of the among-family variance to the total (phenotypic) variance as well as the high heritabilities of growth and susceptibility to frost and Spaherulina musiva showed a high potential for selection for these traits while the quality traits were under low genetic control. Some families showed gains for several traits, suggesting the possibility of developing a selection index to obtain superior families that show gain for not only growth but quality and adaptive traits as well. Type B correlations were high, suggesting that families responded in the same way regardless of the site. High type A correlation between growth traits at 3 and 6 years showed early selection potential, although these relationships should be confirmed with future measurements to evaluate this effect at maturity. These results can be integrated into the strategy for improving hybrid poplar parental populations and, in the longer term, will make it possible to optimize the selection of individuals with traits of interest for the operational deployment of hybrid poplar clones.
