Fine-root production in small experimental gaps in successional mixed boreal forests

The effects of small 10 m x 10 m experimental above-ground gaps on fine-root production for the first two years were studied in three fire-initiated stands of the northwestern mixed broad-leaf-conifer boreal forest of Quebec. The 48-yr-old forest is dominated by Populus tremuloides (Trembling aspen), the 122-yr-old forest by a mixture of P. tremuloides, Abies balsamea (balsam fir) and Picea glauca (white spruce), and the 232-yr-old forest by Thuja occidentalis (eastern white cedar) and A. balsamea, with some P. tremuloides. 40 root-ingrowth bags were installed in different locations in and around each gap (at gap center, 1 to 2 m either side of gap edge and in adjacent control plots). Half of the ingrowth bags were harvested after one year following gap creation, the other half after two years. Roots were sorted into different species grouping. Fine-root production was statistically (P < 0.05) larger in the youngest forest compared to the two older ones after one year, but not after two years. The individual species or groups of species increased, decreased or showed no change in fine-root production in gaps, but overall we did not observe a major shift in species proportion between gap and control plots after two years. Some herbs and also Taxus canadensis seemed to benefit in terms of fine-root growth from such small openings after two years. No statistical differences (P > 0.10) in total fine-root production were found among locations within and outside gaps in either year. However, there was a clear tendency for fine-root production to be smaller in gap center than in the other locations for the two younger successional forests the first year after gap creation. We conclude that small above-ground gaps (i.e. < 100 m2) do not produce a significant and long-lasting below-ground gap in terms of total fine-root production in the successional forests investigated

Overstory influences on light attenuation patterns and understory plant community diversity and composition in southern boreal forests of Quebec

We have characterized overstory light transmission, understory light levels, and plant communities in mixedwood boreal forests of northwestern Quebec with the objective of understanding how overstory light transmission interacts with composition and time since disturbance to influence the diversity and composition of understory vegetation, and, in turn, the further attenuation of light to the forest floor by the understory. Overstory light transmission differed among three forest types (aspen, mixed deciduous-conifer, and old cedar-dominated), with old forests having higher proportions of high light levels than aspen and mixed forests, which were characterized by intermediate light levels. The composition of the understory plant communities in old forests showed the weakest correlation to overstory light transmission, although those forests had the largest range of light transmission. The strongest correlation between characteristics of overstory light transmission and understory communities was found in aspen forests. Species diversity indices were consistently higher in aspen forests but showed weak relationships with overstory light transmission. Light attenuation by the understory vegetation and total height of the understory vegetation were strongly and positively related to overstory light transmission but not forest type. Therefore, light transmission through the overstory influenced the structure and function of understory plants more than their diversity and composition. This is likely due to the strong effect of the upper understory layers, which tend to homogenize light levels at the forest floor regardless of forest type. The understory plant community acts as a filter, thereby reducing light levels at the forest floor to uniformly low levels

Mountain maple and balsam fir early response to partial and clear-cut harvesting under aspen stands of northern Quebec

This study is a component of the Sylviculture et am

Temporal, spatial, and structural patterns of adult trembling aspen and white spruce mortality in Quebec's boreal forest

Temporal, spatial, and structural patterns of adult trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) mortality were studied in intact 150-year-old stands in the southwestern boreal forest of Quebec. For both species, mortality decreases (number of dead trees/total number of trees) with distance from the lake edge until 100-150 m, from which point it slightly increases. Strong peaks in mortality were found for 40- to 60-year-old aspen mainly between 1974 and 1992. Such mortality in relatively young aspen is likely related to competition for light from the dominant canopy trees. Also, the recruitment of this young aspen cohort is presumably the result of a stand breakup that occurred when the initial aspen-dominated stand was between 90 and 110 years old. For spruce, strong peaks in mortality were found in 110- to 150-year-old trees and they occurred mainly after 1980. No clear explanation could be found for these peaks, but we suggest that they may be related to senescence or weakening of the trees following the last spruce budworm outbreak. Suppressed and codominant aspen had a much higher mortality ratio than spruce in the same height class, while more surprisingly, no difference in mortality rate was found between dominant trees of the two species. Most spruce trees were found as standing dead, which leads us to reject the hypothesis that windthrow is an important cause of mortality for spruce in our forests

Modification of functional connectivity in patients with epilepsy: a clustering technique for subject vs. group

Analysis of resting–state (RS) functional networks is a new concept in neuroimaging, which consists in studying slow fluctuations of hemodynamic activity. These fluctuations can be evaluated using the blood-oxygen-level dependent (BOLD) signal measured with functional magnetic resonance imaging (fMRI). Studies have demonstrated that these patterns are organized in space and highly reproducible from subject to subject: the so-called consistent RS networks (RSNs). Assuming that RS activity of patients with epilepsy is affected even when no epileptic activity is observed, the objective of the study is to propose a methodology to identify potential abnormal individual-level networks of patients with epilepsy and to investigate whether the identification of these RSNs could be of some clinical relevance. To do so, we have developed a technique to detect "aberrant" RSNs, as outliers from consistent RSNs extracted from a healthy control population. The identification of RSNs at a group and individual levels was obtained using a spatial clustering technique, the so-called Bootstrap Analysis of Stable Clusters (BASC) (Bellec, Rosa-Neto et al. 2010), which is a statistical framework assessing the stability of the RSNs at the group and at the individual level. Based on the results of BASC, we developed a method to identify, for each patient, the outlier RSNs that statistically differ from the consistent RSNs of the healthy population, thus suggesting the occurrence of aberrant networks.The proposed detection method was evaluated using simulated data (real RS fMRI data on which we added random signals and structured signals at different signal to noise ratio levels) in an attempt to assess its performance and limitations. We demonstrated that the proposed method was highly robust to random noise interference and sensitive to correlated variations between brain structures. Therefore, the proposed method seems promising for future clinical investigation of neurological disorders or drug testing by identifying functionally aberrant networks. This complementary information regarding the abnormal interactions between specific brain regions and other functional network could provide relevant information regarding the extent of a disease.L'analyse de réseaux fonctionnels au repos est un concept récent en neuroimagerie qui consiste en l'étude de fluctuations lentes d'activité hémodynamique. Ces fluctuations peuvent être observées grâce au signal BOLD (Blood oxygenation level dependant) provenant de l'imagerie par résonance magnétique fonctionnelle (IRMf). Plusieurs études ont démontré l'existence d'une organisation spatiale de ces fluctuations lentes, et que cette organisation est hautement reproductible d'un sujet à l'autre: cette organisation spatiale est représentée sous forme de réseaux fonctionnels appelés "consistent resting state networks" (CRSNs). En supposant que l'activité cérébrale d'un sujet épileptique au repos est affectée même pendant les périodes où aucune activité épileptique n'est observée, l'objectif de cette étude propose une méthodologie pour identifier des réseaux fonctionnels potentiellement anormaux au niveau individuel et déterminer si ces derniers peuvent avoir un intérêt clinique. Pour ce faire, nous avons développé une technique de détection de réseaux fonctionnels anormaux en état de repos en partant de l'hypothèse qu'ils diffèrent radicalement des réseaux identifiés chez une population contrôle de sujets sains. L'identification des réseaux fonctionnels au niveau du groupe ou au niveau individuel a été obtenue par une technique de classification spatiale dénommée "Bootstrap Analysis of Stable Clusters" (BASC) (Bellec, Rosa-Neto et al. 2010), un outil d'analyse statistique de réseaux fonctionnels fournissant une mesure de stabilité des différents réseaux identifiés tant au niveau du groupe qu'au niveau individuel. En nous basant sur les résultats fournis par BASC, nous avons développé une méthode d'identification des réseaux aberrants (divergeant significativement de ceux identifiés chez notre population de contrôle) et ce pour chaque patient. La méthode de détection a été évaluée sur des données simulées (de vraies données IRMf acquises durant une période de repos, auxquelles sont ajoutés des signaux aléatoires ou structurés ayant différents rapports signal sur bruit) afin de d'estimer les limitations et performances de la méthode. Nous avons démontré que cette méthode est hautement robuste aux interférences provenant de bruit aléatoire et sensible aux variations de corrélation entre différentes structures cérébrales. De ce fait, la méthode proposée semble prometteuse pour de futures investigations cliniques portant sur des maladies neurologiques ou sur l'impact de certains médicaments sur les réseaux fonctionnels. La méthode permettrait d'identifier les régions dépeignant une organisation fonctionnelle aberrante par rapport à ce qui est identifié au sein d'une population de sujets contrôle. Cette information complémentaire, portant sur l'interaction anormale de certaines régions du cerveau avec d'autres réseaux fonctionnels, pourrait fournir une piste intéressante en ce qui a trait à l'étendue spatiale de la maladie

Partition in 7 networks from a parcellation of 100 regions

Data for multisite pape