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.
by Audrey Verreault | 29 April 2021
Published in Journal of Near Infrared Spectroscopy 28(5-6): 308-314. https://doi.org/10.1177/0967033520950516
Terpenes are phytochemicals found in multiple plant genera, especially aromatic herbs and conifers. Terpene content quantification is costly and complex, requiring the extraction of oil content and gas chromatography analyses. Near infrared (NIR) spectroscopy could provide an alternative quantitative method, especially if calibration can be developed with the spectra of dried plant material, which are easier and faster to acquire than oil-based spectra. Here, multispecies NIR spectroscopy calibrations were developed for total terpene content (mono- and sesquiterpenes) and for specific terpenes (α-pinene, β-pinene and myrcene) with five conifers species (Picea glauca, Picea rubens, Pinus resinosa, Pinus strobus and Thuja occidentalis). The terpene content of fresh shoot samples was quantified with gas chromatography. The NIR spectra were measured on freeze-dried samples (n = 137). Using a subset of the samples, modified partial least squares regressions of total terpene and the three individual terpenes content were generated as a functions of the NIR spectra. The standard errors of the internal cross-validations (values between 0.25 and 2.28) and the ratio of prediction to deviation ratios (RPD values between 2.20 and 2.38) indicate that all calibrations have similar accuracy. The independent validations, however, suggest that the calibrations for total terpene and α-pinene content are more accurate (respective coefficient of determination: r2 = 0.85 and 0.82). In contrast, calibrations for β-pinene and myrcene had a low accuracy (respectively: r2 = 0.62 and 0.08), potentially because of the low concentration of these terpenes in the species studied. The calibration model fits (i.e., r2) are comparable to previously published calibration using the spectra of dried shoot samples and demonstrate the potential of this method for terpenes in conifer samples. The calibration method used could be useful in several other domains (e.g. seedling breeding program, industrial), because of the wide distribution of terpenes and especially of pinenes.
by Audrey Verreault | 29 April 2021
Published in Journal of Vegetation Science 32:e12945. https://doi.org/10.1111/jvs.12945
Aims: Selective browsing can be a chronic disturbance that reduces the survival, growth and reproduction of individual species and shapes the composition and structure of plant communities. Along with other disturbances that perturb the forest ecosystem, browsing may thus affect forest regeneration and successional trajectories after an acute perturbation such as clear-cutting. However, effects of different browsing pressures on plant species, communities and ultimately succession remain hard to predict.
Methods: We implemented a browsing exclusion experiment (n = 15 sites) along a gradient of moose browsing pressure to investigate how this factor influenced the early-successional trajectory of boreal forests following clear-cutting in eastern Canada. We used Principal Response Curve analyses to compare the trajectory of the plant communities depending on site-specific moose browsing pressure and analyzed the trajectory of individual species leveraging these curves.
Results: Our results show that all browsing pressures lead to alterations in plant communities when compared to exclosures, but the effect was stronger under heavier browsing pressure. Under heavier browsing pressure, we observed a lower ground cover of balsam fir, an increased ground cover of raspberry, reaching more than 60%, and a lower abundance of saplings for balsam fir, birches, and rowan.
Conclusion: This study demonstrated that forest response to browsing is a function of local browsing pressure and that moose mainly slowed forest succession toward a closed canopy. However, heavier browsing pressure, through reduced sapling abundance and the resulting increased cover of competitive raspberry, may delay forest succession and push the ecosystem toward an alternative successional trajectory. As heavy selective browsing can interact with anthropogenic disturbances to determine forest succession, we recommend strong integration of the forest and wildlife management sectors to promote sustainability.
by Audrey Verreault | 29 April 2021
Published in Forests 11(11): 1138. https://doi.org/doi:10.3390/f11111138
Forest vegetation management can improve planted seedling survival and growth and is thus widely used in plantation silviculture. In some jurisdictions, mechanical release using brushsaws has replaced the traditional use of chemical herbicides for forest vegetation management purposes. However, its associated costs and the increasing difficulty of finding qualified labor represent a challenge. The browsing of competition by large herbivores may represent an alternative to mechanical release when planted seedlings are resistant to browsing. Here, we compare the efficacy of moose browsing relative to mechanical release in controlling competing vegetation and in promoting white spruce growth in plantations. In a high moose density region, we used an experimental design consisting of four pairs of moose exclosures and unfenced plots; fifty percent of both the access-restricted and unrestricted study areas received a mechanical release treatment. Moose browsing was more efficient than mechanical release in diminishing the sapling density and basal area of competing species. Mechanical release only reduced the sapling density of taller competitors (height > 201 cm), whereas browsing reduced the sapling densities of competitors across a greater size range (height > 130 cm). These effects of moose browsing on competition translated into a greater positive effect of moose browsing on the basal area of planted spruces. We attribute the higher effectiveness of moose browsing relative to mechanical release to its chronic nature. Moose browsed continuously throughout the year and for multiple years, whereas mechanical release was applied only one time between the second and fourth years after planting. Our results suggest that pairing wildlife management and silviculture decisions could be in the best interest of both the hunting and forestry industries in regions where plantations are frequent and use browse-resistant crop trees. Favouring browsers in controlling the density of competing species could increase the hunting experience and income, while providing an e ective, cost-free, and socially acceptable forest vegetation management service.
