Impacts des conditions pré-récolte sur l’efficacité des traitements sylvicoles dans la pessière à mousse de la ceinture d’argile du Québec

Dans l'écosystème forestier, les perturbations naturelles telles que les feux ont une grande influence sur la composition et la structure de la forêt. La ceinture d’argile du Québec est caractérisée par des cycles de feux relativement longs qui facilitent le processus de paludification réduisant la productivité du site à long terme sans l’intervention humaine. Ce n’est que suite à des feux sévères que la couche organique peut être diminuée et que la productivité des sites puisse se rétablir. L’aménagement forestier dans la ceinture d’argile vise donc à utiliser des traitements sylvicoles qui perturbent fortement la couche de sol. Ces traitements sylvicoles consistent à assurer à long terme la continuité des fonctions écologiques de l'écosystème forestier. Néanmoins, l'impact d’une perturbation sur le sol ne dépend pas seulement de la sévérité de la perturbation, mais aussi des conditions pré-perturbation. Cette étude examine comment 1) les conditions pré-récolte influencent la sévérité des traitements sylvicoles et 2) comment la composition du sous-bois répond à ces traitements. L'étude a été effectuée dans la région de la ceinture d’argile dans neuf (9) blocs expérimentaux, chacun d’au moins 20 ha. La récolte a été suivie par deux techniques de préparation mécaniques du sol (PMS). La herse forestière et le scarificateur T26 ont été assignés de façon aléatoire aux neuf sites traités. Le troisième traitement, qui a été perturbé uniquement par la récolte, a été considéré comme le témoin. Des données sur la composition et la couverture de plantes vasculaires et non vasculaires, ainsi que sur l’épaisseur des différentes couches de la matière organique (fibrique, mésique et humique) avant et après coupe, ainsi qu’après PMS ont été récoltées. Les résultats ont montré que l’épaisseur de la couche organique et l‘abondance des bryophytes pré-récolte avaient une relation avec la proportion de la couche organique réduite par la PMS ainsi que l’exposition des différentes couches de sol. Par ailleurs, le taux de décomposition était plus élevé dans les sites traités par rapport aux sites témoins. Bien que la herse ait causé un plus gros changement dans les concentrations des éléments nutritifs du sol que le traitement du T26, la concentration de l'azote et du phosphore disponible aux plantes n'a pas affectée. En outre, la fréquence et l’abondance de la composition des bryophytes et des graminoïdes ont été plus affectées par la herse que par le T26. En revanche, l’abondance de Kalmia angustifolia L. et Rhododendron groenlandicum (Oeder) Kron & Judd n'a pas été affecté significativement différente entre les traitements. Cette étude suggère que même si les conditions pré-récolte ont affecté l’efficacité des traitements sylvicoles, les PMS ont pu créer plus de microsite de bonne qualité ainsi d’augmenter les taux de décomposition. En outre, il n'y avait pas de différence entre l'effet créé par les deux techniques de PMS suggérant que l'utilisation de l'une ou l’autre des techniques peut créer suffisamment de microsites favorables. Puisque l'objectif de ce projet est de réduire le taux de paludification et d’augmenter la productivité du site, des suivis seront nécessaires pour examiner à plus long terme l'effet des différents traitements sur la croissance des arbres, les éléments nutritifs et l’abondance des éricacées

Mid- and long-term effects of stock type on the growth and yield of spruce seedlings in a non-herbicide scenario

Stock types used in reforestation projects can influence plantation success, as they determine the morphological attributes of the planted seedlings. They can also interact with silviculture treatments to influence early seedling survival and growth. As nurseries develop and produce new stock types in response to –and in interaction with– manager needs, research efforts must be pursued to validate early seedling performance and long-term growth and yields. In this context, we aimed to evaluate the main and interactive effects of mechanical site preparation and stock type on planted black (Picea mariana [Mill.] BSP) and white spruce (P. glauca [Moench.] Voss) seedling dimensions at 16-y, and estimate the long-term impact of stock type on the merchantable volume at rotation age for white spruce. We hence compared medium (200 cm3 root plug) and large (350 cm3 root plug) containerized seedlings, as well as large bare-root seedlings of both species, in a field experiment established in Quebec (Canada), where there is a ban on the use of chemical herbicides for vegetation management treatments. Our results confirm that there is a significant, although limited impact of stock type on the size of black and white spruce at the juvenile stage, when medium and large stock types are compared, but that these small differences have a negligible effect on the estimated merchantable volume produced at rotation age (60 years). Mechanical site preparation does not promote seedling growth on these rich sites with thin humus. Therefore, selection of a medium or larger stock type for reforestation projects and application of mechanical site preparation in ecosystems similar to the one studied here should be based on other considerations than growth and yield, such as seedling availability, production and planting costs, or operational constraints

Regional Climate, Edaphic Conditions and Establishment Substrates Interact to Influence Initial Growth of Black Spruce and Jack Pine Planted in the Boreal Forest

In eastern Canada, spruces (Picea spp.) and pines (Pinus spp.) are among the main commercial species being logged for their lumber or wood fiber. Annually, about 175 million seedlings are planted in areas totaling ~100,000 ha. Appropriate microsite selection is essential during reforestation operations, given that it can improve the chances of survival and initial growth of the seedlings. In fir (Abies spp.) and spruce forests of eastern Canada, the optimal characteristics of establishment microsites have yet to be identified; these would be determined by different physical and climatic variables operating at several scales. Our study determined the influence of climatic (regional-scale), edaphic (stand-scale), local (microsite-scale) and planting conditions on the establishment substrate and initial growth of black spruce (Picea mariana Britton, Sterns and Poggenb.) and jack pine (Pinus banksiana Lamb.). Substrate characterization and growth monitoring (three growing seasons) for the two species were conducted on 29 planted cutblocks that were distributed over an east-west climatic gradient (precipitation and temperature) in the balsam fir and black spruce-feather moss forests of Quebec (Canada). Linear mixed models and multivariate analyses (PCAs) determined the effects of climatic, edaphic and micro-environmental variables and their interactions on the establishment substrate and seedling initial growth. The predictive models explained, respectively, 61% and 75% of the growth variability of black spruce and jack pine. Successful establishment of black spruce and jack pine depended upon regional conditions of precipitations and temperature, as well as on their interactions with stand-scale edaphic variables (surface deposit, drainage and slope) and local variables (micro-environmental) at the microsite-scale (establishment substrate types and substrate temperature). Mineral, organo-mineral and organic establishment substrates exerted mixed effects on seedling growth according to regional precipitation and temperature conditions, as well as their interactions with edaphic and local variables at the stand and microsite-scales, respectively

Exploring the potential of two-aged white spruce plantations for the production of sawlog volume with simulations using SORTIE-ND

The main objective for even-aged plantation (EAP) management of producing sawlog material has driven practices towards low initial planting densities and lower post thinning densities. For semi-shade tolerant species, the resulting stand density potentially leaves enough growing space for the introduction of a second cohort of trees in the understory, making it a two-aged plantation (TAP). TAPs could have many silvicultural benefits, especially in sensitive areas where intensive treatments associated with EAPs are incompatible with local management objectives. White spruce (Picea glauca) is a good candidate species for modeling TAPs because it is the most widely planted tree species in Canada and has proven tolerance to understory planting. SORTIE-ND, a single-tree spatially explicit growth model was used to explore the yield of variable density and rotation length scenarios when each white spruce cohort is introduced mid rotation, compared to traditional even-aged management. All TAP scenarios tested produced more sawlog volume and more merchantable volume than equivalent densities of EAPs. The lowest density tested, 400 stems ha-1 planted every 35 years, had the highest sawlog yields (3.23 m3 ha-1 yr-1). Considering smaller size products changes the optimum TAP scenario but maintains the advantage over EAPs

Issues and perspectives on the use of exotic species in the sustainable management of Canadian forests

Plantations offer a high potential to respond to the increasing pressure on forests to deliver social, economic, and environmental services. Exotic tree species have a long history of use in plantation forestry, mostly because of their improved productivity compared with that of native species. Because of their impacts on land management and the environment, questions arise regarding the compatibility of exotic tree plantations with sustainable forest management (SFM), the overarching paradigm driving forest legislations in Canada. Our objectives were thus to i) briefly review the historical and current use of exotic tree species in Canada, ii) identify the social, economic and environmental issues related to the use of exotic tree species in Canadian forestry, based on sustainable forest management criteria, and iii) identify perspectives related to the use of exotic tree species in the sustainable management of Canadian forests. Results show that six out of ten Canadian provinces do not have specific legislations to control the use of exotic tree species for reforestation within their borders. The use of exotic tree species is mainly controlled through third-party certification agencies. Exotic tree species represent a small proportion of the planted seedlings in Canada and Norway spruce is the most common one. The use of exotic tree species is compatible with sustainable forest management criteria used in Canada, but forest managers must take into account several issues related to their use and maintain a social license to be entitled to plant them. Issues are highly dependent upon scale. The zoning of management intensity could provide environmental, economic and social benefits, but costs/benefits analyses should be carried out. The concept of naturalness could also be useful to integrate plantations of exotic species in jurisdiction where SFM strategies are based on ecosystem management principles. Monitoring of hybridization and invasiveness of exotic species must be included in landscape analyses to forestall loss of resilience leading to compromised structural and functional ecosystem states. The use of exotics species is recognized as a tool to sequester carbon and facilitate adaptation of forests to global changes, but it is necessary to carefully identified contexts where assisted migration is justified and disentangle planned novel ecosystems coherent with global changes generated by assisted migration from those emerging from invasive species forming undesired states

Impact de la neuromodulation des cortex dorsolatéraux préfrontaux sur le traitement des émotions : une perspective électrophysiologique chez l'humain

La neuromodulation non-invasive appliquée au niveau des cortex dorsolatéraux préfrontaux (CDLPF) est utilisée dans le traitement des troubles dépressifs majeurs. Or, ces troubles sont caractérisés par un traitement des informations émotionnelles anormal. Donc, il se pourrait que l'impact bénéfique sur l'humeur de la neuromodulation soit généré par une amélioration du traitement des émotions. Le but de ce projet de maîtrise était de déterminer l'impact de la neuromodulation appliquée au niveau des CDLPF sur le traitement des émotions chez les individus en santé. Pour ce faire, nous avons mené une revue de la littérature des études de neuromodulation ayant pour but de modifier le traitement des émotions ou l'humeur chez le sujet sain. Les résultats de cette revue suggèrent que la neuromodulation modifie peu ou pas l'humeur, mais qu'elle influence le traitement des émotions. Bien que ces études contribuent aux connaissances quant aux substrats neuronaux du traitement des émotions, elles renseignent peu sur les mécanismes neurophysiologiques impliqués. Nous avons donc mené une seconde étude afin de vérifier l'hypothèse si l'un de ces mécanismes était relié aux oscillations électrophysiologiques enregistrées dans la bande alpha (8 -12 Hz), laquelle a été associée au traitement des émotions. Nous avons choisi d'étudier comme traitement des émotions le biais attentionnel (BA) envers les émotions chez le sujet sain et d'utiliser comme technique de neuromodulation la stimulation transcrânienne par courant alternatif (StCA) afin d’amplifier la puissance du signal alpha. Les résultats proposent que la StCA ne module pas l’amplitude de la bande alpha enregistrée au niveau de F3 et F4 (régions préfrontales), ni le BA envers les émotions. Toutefois, ces résultats négatifs sont à interpréter avec prudence étant donné que cette étude est préliminaire. En conclusion, il est possible de modifier le traitement des émotions par la neuromodulation appliquée au niveau des CDLPF, mais les mécanismes de cette modification demeurent essentiellement inconnus.Noninvasive neuromodulation targeting the dorsolateral prefrontal cortex (DLPFC) is used to treat major depressive disorder. Major depressive disorder is characterized by emotional processing deficits. However, mechanics of action remain unclear. A potential mechanism underlying this clinical benefit might involve modulation of emotional processing, which in turn would alleviate depressive mood. The goal of this master thesis was to contribute to this field by studying the impact of neuromodulation applied over the DLPFC on emotional processing in healthy individuals by conducting a review of the literature and a proof-of-principle study in healthy adults. The literature review suggests that neuromodulation does not significantly modify mood but influences emotional processing in healthy participants. Because it indicates the importance of the DLPFC in emotional processing, we thus conducted a second study to examine whether one mechanism of action involves modulation of frontal oscillations of the alpha band (8 – 12 Hz), which is known to be implicated in emotional processing. We chose to study attentional bias (AB) to emotion with transcranial alternating current stimulation (tACS) in order to increase alpha power. Results suggest that tACS did not significantly influence alpha power at F3 and F4 (prefrontal regions) or emotional AB. These results are, however, to be interpreted with caution as this was a preliminary study. In conclusion, it is possible to modify emotional processing with the neuromodulation of the DLPFC, but the mechanisms of these modifications still mostly unknown