by Audrey Verreault | 29 April 2021
Published in Frontiers in Earth Science 8(514). https://doi.org/10.3389/feart.2020.556781
Asynchronous hydroclimatic modeling is proposed for the construction of physically based streamflow projections over regions characterized by meteorological observation scarcity. The novel approach circumvents the requirement for meteorological observations by 1) calibrating quantile mapping transfer functions simultaneously to the parameters of the hydrologic model, 2) forcing the hydrologic model with post-processed climate simulations, and 3) intentionally ignoring the correlation between simulated streamflow values and observations. As a result, relative humidity, solar radiation and wind speed are integrated to a full hydroclimatic modeling chain, allowing the construction of streamflow projections forcing the Penman-Montheith reference evapotranspiration formulation over a forested catchment that flows into the St-Lawrence River, Canada. Results confirm a more accurate simulated hydrological response relative to a conventional hydroclimatic modeling chain employing reanalyses as description of the climate system. They also highlight the contribution to uncertainty in streamflow projections from biased climate variables issued by the reanalyses. The suggested framework assumes the hydrologic regime as a functional proxy to corresponding climate drivers. We believe the latter opens promising perspectives in the scope of producing more reliable estimations of water-related and energy-driven processes such as streamflow generation, snow accumulation and melt, river ice jams, water temperature, or vegetation growth under evolving climate conditions.
by Audrey Verreault | 29 April 2021
Published in Forests 11(9): 929. https://doi.org/10.3390/f11090929
Species with wide geographical ranges exhibit specific adaptations to local climates, which may result in diverging responses among populations to changing conditions. Climate change has advanced spring phenology worldwide, but questions of whether and how the phenological responses to warming differ among individuals across the natural range of a species remain. We conducted two experiments in January and April 2019, and performed daily observations of the timings of bud break in 1-year-old seedlings of sugar maple (Acer saccharum Marshall) from 25 Canadian provenances at two thermal conditions (14/10 and 18/14 °C day/night temperature) in a controlled environment. Overall, bud break started 6 days from the beginning of the experiments and finished after 125 days. The earlier events were observed in seedlings originating from the colder sites. Bud break was delayed by 4.8 days per additional degree Celsius in the mean annual temperature at the origin site. Warming advanced the timing of bud break by 17–27 days in January and by 3–8 days in April. Similar advancements in bud break were observed among provenances under warming conditions, which rejected our hypothesis that sugar maple populations have different phenological responses to warming. Our findings confirm the differentiation in ecotypes for the process of bud break in sugar maple. In cases of homogenous spring warming across the native range of sugar maple, similar advancements in bud phenology can be expected in different populations.
by Audrey Verreault | 29 April 2021
Published in Journal of Near Infrared Spectroscopy: 0967033520967324. https://doi.org/10.1177/0967033520967324
A near infrared (NIR) spectrometer, equipped with a 2-mm diameter fiber optic probe, was used to develop a rapid and automated method for determining the radial profiles of wood properties for six tree species of the boreal forest of eastern Canada. Partial least squares regressions were performed using individual spectra, collected every 5 mm, from the pith to the bark, using 1,538 samples previously scanned by SilviScan to provide reference data. Results obtained for density (r2 of 0.57 to 0.65; SE of 21 to 33 kg/m3), microfibril angle (0.56 to 0.82, 2.3 to 4.8°) and modulus of elasticity (0.71 to 0.85, 1.3 to 1.8 GPa) were suitable for the purpose of this study. This method was then applied to more than 30,000 tree cores and the resulting radial profiles of the properties were consistent with literature. Area-weighted average predictions also gave reliable estimates at the disk scale. NIR-estimated values were strongly correlated to the measured density (r of 0.83 to 0.93) and modulus of elasticity (0.82 to 0.88) and moderately correlated to measured microfibril angle (0.64 to 0.78). Radial profiles of wood properties are needed to characterize the proportions of juvenile and mature wood. The developed method therefore offers interesting opportunities for estimating the quality of wood fiber in trees growing in plantation or natural forest.
by Audrey Verreault | 29 April 2021
Published in Forest Ecology and Management 478: 118514. https://doi.org/10.1016/j.foreco.2020.118514
In order to compensate for regeneration failure of red spruce (Picea rubens) in the managed temperate mixedwood forest, an enrichment planting study was conducted in yellow birch (Betula alleghaniensis)–conifer stands, in Quebec, Canada. The experimental design compared four cutting treatments: an uncut control (26 m2·ha−1 of merchantable basal area [BA], with mean natural canopy gap areas of ≤ 100 m2 each) and three hybrid single-tree and group-selection cuttings corresponding to a light cut (20% removal; residual BA [RBA]: 21 m2·ha−1; mean harvest gap area: 220 m2), a moderate cut (31% removal; RBA: 18 m2·ha−1; gap area: 270 m2), and a heavy cut (42% removal; RBA: 15 m2·ha−1; gap area: 340 m2). In the cuts, large-sized containerized seedlings of red spruce were planted within harvest gaps, while in the control, seedlings were planted systematically, for comparison. Three years later, a mechanical release treatment was applied in half of planted plots to limit competing vegetation. After eight years, seedling survival in the three cuts was equally high (> 80%), and greater than in the control (40%). Morphophysiological performance of seedlings was best in the heavy cut creating the largest gaps. In general, the release treatment enhanced survival in the control and in the light cut with the smallest gap sizes. Release also improved morphophysiological performance (which, however, remained suboptimal) in all cutting treatments, but especially in the heavy cut. Although red spruce is highly shade-tolerant, the low survival and performance in the control suggest that for this species, seedlings grown with traditional forest nursery practices are not adapted to plantation under a closed canopy. Results indicate that enrichment planting in intermediate-size harvest gaps (of about 340 m2 in area) of partially cut stands (of about 40% in BA) combined to mechanical release could be a good strategy to maintain or reintroduce red spruce and promote its morphophysiological performance.
by Audrey Verreault | 29 April 2021
Published in Frontiers in Forests and Global Change 3(121). https://doi.org/10.3389/ffgc.2020.581363
The increase in soil organic matter mineralization rate in boreal forests that may result from global warming is a major concern as it could release large amounts of C to the atmosphere. On the other hand, this may also release N to the soil and stimulate tree growth, which could partly offset the C losses from the soil. The long-term interaction between increased N deposition and soil warming on soil organic N mineralization and tree growth is still uncertain in the boreal zone. In this study, soil temperature was increased by +2–4°C from April to July with heating cables for a period of 9 years and N was applied above the canopy of mature stands from June to September for 7–9 years in two eastern Canada boreal forests [Bernatchez (BER) and Simoncouche (SIM)]. We assessed the effects of these treatments on organic N mineralization rate and on the growth, phenology and foliar N of Abies balsamea (L.) Mill. (balsam fir; BF) and Picea mariana (Mill.) BSP (black spruce; BS) seedlings. The soil warming (SW) treatment had no significant effect on N mineralization rates, whereas canopy N addition (CNA) decreased gross N mineralization rate by 23% and forest floor’s alkyl/O-alkyl C ratio by ∼15% relative to unfertilized plots. Foliar δ15N in the control plots was markedly lower in BS than in BF and at BER than at SIM (–4.8 and –2.9‰ in BS at BER and SIM, respectively; 1.6 and 3.8‰ in BF at BER and SIM, respectively) likely due to a higher contribution of 15N-depleted N derived from mycorrhizal fungi in BS and at BER, the colder and the more N-depleted site. The treatments had non-significant effects on seedling growth and foliar chemistry but SW caused a premature bud outbreak and faster bud development for both species at both sites. Overall, our results show that increased soil temperature and N deposition in boreal forests may not impact soil fertility and vegetation growth as much as previously thought, but climate warming, by initiating earlier and faster bud development, may however expose seedlings to late spring frosts in the future.
