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.
by Audrey Verreault | 28 April 2021
Published in Ecological Indicators 119: 106832. https://doi.org/10.1016/j.ecolind.2020.106832
One-quarter of forest areas worldwide are managed for forestry purposes. Depending upon the type of practice and intensity of management, forestry may alter forests to various degrees and raise sustainability issues. To mitigate the alteration of natural forests by forestry and to promote sustainability, ecosystem management has been implemented widely over the past quarter century. A need remains for the development of comprehensive and operational assessment approaches to validate its effectiveness. Naturalness assessment could be used to validate effectiveness of ecosystem management since this concept relates to the degree to which a natural state has been altered. We developed an approach that integrates stand- and landscape- scale traits of naturalness into a single comprehensive assessment that can be performed using only forestry maps. To illustrate our approach, we assessed naturalness in four managed forest landscapes (2184 km2), representing a management gradient of increasing intensity from passive restoration to plantation forestry. We defined four naturalness classes, i.e., natural, semi-natural, altered and artificial. Assessment was performed in two steps. At step one, we attributed a class to each managed stand by comparing its current composition with natural stand compositions of its potential natural vegetation. At the landscape scale, certain developmental stages or forest types could be in excess in managed forest landscapes compared with natural forest landscapes. At step two, we transferred numbers of stages or types in excess from the natural class to more altered classes. We demonstrated that naturalness decreased as management intensity increased. Passive restoration and extensive management generated a landscape where semi-natural forests predominated in mixtures with a lower abundance of natural forests. Intensive management generated a largely semi-natural forest landscape. Plantation forestry generated a landscape where semi-natural and altered forests predominated. In conclusion, it should now be possible to validate the effectiveness of different practices and intensity of ecosystem management in promoting sustainability, by performing our assessment approach periodically following every update of forestry maps. Our approach could also allow for more comprehensive assessment of forest management strategies developed to mitigate global change by putting into better perspective their potential effects upon forest alteration of various forestry practices that have been implemented to sequester carbon.
by Audrey Verreault | 28 April 2021
Published in Energies 13(18): 4609. https://doi.org/doi:10.3390/en13184609
Natural disturbances are common in Canadian boreal managed forests. For example, during and after insect epidemics, foresters must deal with significant amounts of degraded or dead wood that cannot be processed into sawn timber or pulp. Bioenergy could be an alternative pathway for this wood. A case study in Quebec (Canada) was used to evaluate the profitability of pellet production for bioenergy using degraded trees from insect epidemics. A bioenergy scenario was simulated in which degraded trees were harvested for bioenergy alongside sound wood for timber and pulp. This scenario was compared to a reference scenario in which degraded trees were left on cutovers. Using wood pellets as a case study, the results showed that at current market prices, harvesting degraded trees for pellet production is not as profitable as leaving them in the forest. Nevertheless, the overall forest operations for procuring wood for timber and pulp were still profitable, even with very high degradation levels. Procuring degraded trees reduced the overall fixed costs per harvested m3 and allowed average savings of C$2.83/harvested m3. The silvicultural savings associated with lower site preparation needs following procurement of degraded trees ranged from C$0/ha to C$500/ha, resulting in average savings of C$2.31/harvested m3. Depending on the stand conditions, the distribution of fixed costs and silvicultural savings of biomass procurement could be either low or significant.
