Reconstitution dendrochronologique et fréquence des grosses avalanches de neige dans un couloir subalpin du mont Hog’s Back, en Gaspésie centrale (Québec)

Cette étude porte sur l’activité des grosses avalanches de neige dans un couloir de 660 m de longueur, sur le versant est du mont Hog’s Back, en Gaspésie centrale (Québec). L’analyse dendrochronologique des arbres échantillonnés dans la zone d’arrivée des coulées de neige a permis de faire ressortir 35 événements survenus entre 1895 et 1996, ce qui correspond à un intervalle de retour des grosses avalanches de près de 3 ans et à une fréquence ou probabilité d’incidence annuelle d’environ 34 %. Les décennies 1950 et 1980 rassemblent le plus grand nombre d’événements, respectivement 5 et 6 grosses avalanches, et la décennie 1930, aucun. La probabilité annuelle d’incidence de grosses avalanches dans le couloir étudié a été évaluée à 27 % et 41 % respectivement pour la première (1895-1945) et la seconde (1946-1996) parties du XXe siècle. Les données sur les précipitations de neige obtenues d’une station (Cap-Seize) située à proximité du couloir étudié montrent qu’entre 1969 et 1994, 8 des 13 années de grosses avalanches (62 %) ont enregistré des précipitations totales de neige supérieures à la moyenne (457 cm). Les facteurs d’ordres topographique, écologique et climatique favorisant le déclenchement d’avalanches en Gaspésie centrale sont aussi abordés.High-magnitude snow avalanche activity was studied in a 660-m long avalanche track on the east slope of Mont Hog’s Back in central Gaspésie (Québec). Tree-ring data from trees growing in the runout zone, which were damaged during snow wasting events, indicated that 35 high-magnitude avalanches occurred between 1895 and 1996, which corresponds to a ~3-year return interval with a ~34 % probability that an avalanche will occur in any one year. The highest number of events was recorded in the 1950s and the 1980s, with 5 and 6 events, respectively, whereas no avalanche was recorded in the 1930s. A 27 % and 41 % annual frequency or probability of high-magnitude avalanches in the avalanche track studied was calculated for the first (1895-1945) and the second part (1946-1996) of the 20th century. Snowfall from a nearby meteorological station (Cap-Seize) indicated that 8 out the 13 high-magnitude avalanche years (62 %) between 1969 and 1994 had total snowfall above average (457 cm). Geographical, ecological and meteorological factors responsible for avalanche activity in central Gaspésie were also discussed.El presente estudio trata de la actividad de las avalanchas importantes en un corredor de 600 m de largo, en la vertiente este del Mont Hog’s Back, en la región de la Gaspésie central (Québec). El análisis dendrocronológico de los árboles seleccionados en la zona donde atraviesan las caídas de nieve permitió identificar 35 eventos acontecidos entre 1895 y 1996, que corresponden a intervalos de ocurrencia de avalanchas importantes de cerca de 3 años y de una frecuencia o probabilidad de acontecimiento anual cercana al 34 %. Las décadas de 1950 y 1980 reúnen el mayor número de ocurrencia de grandes avalanchas, 5 y 6 respectivamente; mientras que la década de 1930 no registra ninguna. La probabilidad anual de ocurrencia de grandes avalanchas en el corredor estudiado fue estimada entre 27 y 41 % para la primera y la segunda parte del siglo XX, 1895-1945 y 1946-1996 respectivamente. Los registros de caída de nieve obtenidos de la estación de Cap-Seize, situada a proximidad del corredor subalpino, muestran que entre 1969 y 1994, 8 de los 13 años que registran avalanchas importantes (62 %) poseen un nivel de caída de nieve total superior al promedio (457 cm). En el presente manuscrito se discuten también los factores de tipo topográfico, ecológico y climático que favorecen la formación de avalanchas en la región de la Gaspésie central

Émersion des terres et développement des sols bien drainés au lac Guillaume-Delisle, Québec subarctique

Dans la région du lac Guillaume-Delisle, au Québec subarctique, des cônes de déjection d’âge et d’altitude variables se sont déposés tout au cours de l’Holocène sur des plages soulevées, offrant ainsi la possibilité d’étudier une chronoséquence holocène de sols. Le cadre temporel a été établi par la datation radiocarbone de 38 horizons organiques enfouis et la mise à jour de la courbe d’émersion des terres pour la région. L’émersion se serait effectuée selon un taux moyen de 5,6 m/siècle entre 8500 et 4500 années cal. BP et de 1,2 m/siècle après 4500 années cal. BP. Les analyses morphologiques et chimiques ont montré que les sols et paléosols subarctiques sableux, bien drainés et soustraits à l’influence des combes à neige, sont formés principalement par l’accumulation dans l’horizon B de matière organique humifiée combinée à de l’aluminium et du fer (podzolisation). L’enrichissement de l’horizon B en fer et en aluminium se fait lentement en suivant une fonction linéaire. La durée de pédogenèse requise pour obtenir le seuil minimal (Fep+Alp) de 0,4 % pour l’horizon Bf fixé par le Système canadien de classification des sols serait d’environ 12 400 années. Bien que théorique, cette durée indique à quel point les conditions nécessaires à la formation des podzols sont difficiles à réunir dans les sols subarctiques où la végétation demeure basse et le couvert nival peu épais.In the Lake Guillaume-Delisle area, alluvial fans of various ages and elevations were deposited throughout the Holocene over raised beach deposits, which allowed the studying of a subarctic soil chronosequence. The temporal framework is based on 38 14C dates obtained from buried organic soil horizons, and on an update of the Lake Guillaume-Delisle emersion curve. Postglacial uplift due to glacio-isostatic rebound occurred at a mean rate of 5.6 m/century from 8500 to 4500 cal. yr BP, and of 1.2 m/century after 4500 cal. yr BP. Soil morphology and chemistry showed that well-drained sandy soil and paleosoil development, when not influenced by late-lying snowpatches and snowmelt, is characterized by B horizons having a dominant accumulation product of amorphous material composed mainly of humified organic matter combined with Al and Fe (podzolisation). However, pedogenic development is weak and would take about 12 400 years to reach the minimum values of (Fep+Alp) ≥0,4% required for meeting the criteria of a Bf horizon in the Canadian system of soil classification, according to a linear function. Although theoretical, this value indicates that conditions required for Podzol formation are hard to reach in subarctic soils with low vegetation and thin snow cover

Effects of Plant Cover Improvements for Nesting Ducks on Grassland Songbirds

Several islands located along the St. Lawrence River in southern Quebec have been used as natural pastureland by cattle for decades. Recently, a rest-rotation grazing system and dense nesting cover were established on four islands near Varennes to improve duck nesting conditions. The effects of these two plant cover improvements on the abundance of grassland songbirds were assessed through four treatments: (1) idle fields with no vegetation improvement but exclusion of cattle (IDLE), (2) improved pastures with seeding of forage plants for cattle (IMPP), (3) dense seeded nesting cover fields improved for ducks and where cattle were excluded (DNC), and (4) natural or unimproved pastures grazed by cattle after the duck nesting season (UIPP). The overall abundance of birds was similar among treatments before cover improvements as well as two years after. The abundance of Bobolinks (Dolichonyx oryzivorus) was significantly greater in DNC and UIPP two years after treatments while Red-winged Blackbirds (Agelaius phoeniceus) were more abundant in DNC and IDLE. Plant cover improvements had little impact on Savannah Sparrow (Passerculus sandwichensis) abundance. Furthermore, few annual or treatment-related changes were observed for less abundant species. On the short-term, duck nesting cover improvements in natural pastures did not have any major effect on grassland songbirds on Varennes islands

How do polydisperse repulsive colloids crystallize?

A modified version of the Gibbs-ensemble Monte-Carlo method reveals how polydisperse charged colloidal particles can build complex colloidal crystals. It provides general rules that are applicable to this fractionated crystallization that stems from size segregation. It explains the spontaneous formation of complex crystals with very large unit-cells in suspensions of nanoparticles with a broad size distribution

Proteins that bind methylated DNA and human cancer: reading the wrong words

DNA methylation and the machinery involved in epigenetic regulation are key elements in the maintenance of cellular homeostasis. Epigenetic mechanisms are involved in embryonic development and the establishment of tissue-specific expression, X-chromosome inactivation and imprinting patterns, and maintenance of chromosome stability. The balance between all the enzymes and factors involved in DNA methylation and its interpretation by different groups of nuclear factors is crucial for normal cell behaviour. In cancer and other diseases, misregulation of epigenetic marks is a common feature, also including DNA methylation and histone post-translational modifications. In this scenario, it is worth mentioning a family of proteins characterized by the presence of a methyl-CpG-binding domain (MBDs) that are involved in interpreting the information encoded by DNA methylation and the recruitment of the enzymes responsible for establishing a silenced state of the chromatin. The generation of novel aberrantly hypermethylated regions during cancer development and progression makes MBD proteins interesting targets for their biological and clinical implications

Epigenetic engineering shows that a human centromere resists silencing mediated by H3K27me3/K9me3

Centromeres are characterized by the centromere-specific H3 variant CENP-A, which is embedded in chromatin with a pattern characteristic of active transcription that is required for centromere identity. It is unclear how centromeres remain transcriptionally active despite being flanked by repressive pericentric heterochromatin. To further understand centrochromatin’s response to repressive signals, we nucleated a Polycomb-like chromatin state within the centromere of a human artificial chromosome (HAC) by tethering the methyltransferase EZH2. This led to deposition of the H3K27me3 mark and PRC1 repressor binding. Surprisingly, this state did not abolish HAC centromere function or transcription, and this apparent resistance was not observed on a noncentromeric locus, where transcription was silenced. Directly tethering the reader/repressor PRC1 bypassed this resistance, inactivating the centromere. We observed analogous responses when tethering the heterochromatin Editor Suv39h1-methyltransferase domain (centromere resistance) or reader HP1α (centromere inactivation), respectively. Our results reveal that the HAC centromere can resist repressive pathways driven by H3K9me3/H3K27me3 and may help to explain how centromeres are able to resist inactivation by flanking heterochromatin

The seeds of divergence: the economy of French North America, 1688 to 1760

Generally, Canada has been ignored in the literature on the colonial origins of divergence with most of the attention going to the United States. Late nineteenth century estimates of income per capita show that Canada was relatively poorer than the United States and that within Canada, the French and Catholic population of Quebec was considerably poorer. Was this gap long standing? Some evidence has been advanced for earlier periods, but it is quite limited and not well-suited for comparison with other societies. This thesis aims to contribute both to Canadian economic history and to comparative work on inequality across nations during the early modern period. With the use of novel prices and wages from Quebec—which was then the largest settlement in Canada and under French rule—a price index, a series of real wages and a measurement of Gross Domestic Product (GDP) are constructed. They are used to shed light both on the course of economic development until the French were defeated by the British in 1760 and on standards of living in that colony relative to the mother country, France, as well as the American colonies. The work is divided into three components. The first component relates to the construction of a price index. The absence of such an index has been a thorn in the side of Canadian historians as it has limited the ability of historians to obtain real values of wages, output and living standards. This index shows that prices did not follow any trend and remained at a stable level. However, there were episodes of wide swings—mostly due to wars and the monetary experiment of playing card money. The creation of this index lays the foundation of the next component. The second component constructs a standardized real wage series in the form of welfare ratios (a consumption basket divided by nominal wage rate multiplied by length of work year) to compare Canada with France, England and Colonial America. Two measures are derived. The first relies on a “bare bones” definition of consumption with a large share of land-intensive goods. This measure indicates that Canada was poorer than England and Colonial America and not appreciably richer than France. However, this measure overestimates the relative position of Canada to the Old World because of the strong presence of land-intensive goods. A second measure is created using a “respectable” definition of consumption in which the basket includes a larger share of manufactured goods and capital-intensive goods. This second basket better reflects differences in living standards since the abundance of land in Canada (and Colonial America) made it easy to achieve bare subsistence, but the scarcity of capital and skilled labor made the consumption of luxuries and manufactured goods (clothing, lighting, imported goods) highly expensive. With this measure, the advantage of New France over France evaporates and turns slightly negative. In comparison with Britain and Colonial America, the gap widens appreciably. This element is the most important for future research. By showing a reversal because of a shift to a different type of basket, it shows that Old World and New World comparisons are very sensitive to how we measure the cost of living. Furthermore, there are no sustained improvements in living standards over the period regardless of the measure used. Gaps in living standards observed later in the nineteenth century existed as far back as the seventeenth century. In a wider American perspective that includes the Spanish colonies, Canada fares better. The third component computes a new series for Gross Domestic Product (GDP). This is to avoid problems associated with using real wages in the form of welfare ratios which assume a constant labor supply. This assumption is hard to defend in the case of Colonial Canada as there were many signs of increasing industriousness during the eighteenth and nineteenth centuries. The GDP series suggest no long-run trend in living standards (from 1688 to circa 1765). The long peace era of 1713 to 1740 was marked by modest economic growth which offset a steady decline that had started in 1688, but by 1760 (as a result of constant warfare) living standards had sunk below their 1688 levels. These developments are accompanied by observations that suggest that other indicators of living standard declined. The flat-lining of incomes is accompanied by substantial increases in the amount of time worked, rising mortality and rising infant mortality. In addition, comparisons of incomes with the American colonies confirm the results obtained with wages— Canada was considerably poorer. At the end, a long conclusion is provides an exploratory discussion of why Canada would have diverged early on. In structural terms, it is argued that the French colony was plagued by the problem of a small population which prohibited the existence of scale effects. In combination with the fact that it was dispersed throughout the territory, the small population of New France limited the scope for specialization and economies of scale. However, this problem was in part created, and in part aggravated, by institutional factors like seigneurial tenure. The colonial origins of French America’s divergence from the rest of North America are thus partly institutional

Dynamique d’un front forestier sur un talus d’éboulis actif en climat tempéré froid (Gaspésie, Québec)

The development of the forest vegetation on a scree slope located in the valley of Rivière à Pierre, Gaspé Peninsula, was reconstructed over the last two centuries. It was established from dendroecological data that the forest limit was lower than its present position around 1850 and that the forest cover expanded until the middle of the 20th century, in spite of evidence for slope instability at the end of the 19th century. After 1950, the forest edge retreated to its present position. Annual sedimentation rates were calculated by using dendrogeomorphological methods. They were lowest (< 0.1 cm/year) during the second half of the 19th century, and increased to 0.5 cm/year during the 20th century, and up to 1.0 cm/year after 1975. Increased slope activity was likely associated with a higher frequency of frost-coated clast flows.Cette recherche a permis de reconstituer, pour les deux derniers siècles, l'évolution de la végétation forestière sur un talus d'éboulis de la vallée de la rivière à Pierre, en Gaspésie. Les données dendroécologiques ont permis de faire ressortir que la limite supérieure de la forêt était plus basse que la limite actuelle vers le milieu du XIXe siècle, que la végétation forestière a connu une phase d'expansion jusque vers le milieu du XXe siècle, bien que certains signes d'instabilité se soient manifestés dès la fin du XIXesiècle. Le front forestier a régressé jusqu'à sa position actuelle après les années 1950. Le taux annuel moyen de sédimentation, calculé par des méthodes dendrogéomorphologiques, a été inférieur à 0,1 cm pendant la deuxième moitié du XIXe siècle pour ensuite atteindre 0,5 cm/an, puis excéder 1,0 cm/an après 1975. L'activité plus importante dans le versant serait associée à une fréquence accrue des coulées de pierres glacées.Mit Hilfe dieser Forschung konnte man die Entwicklung der Wald-Vegetation auf einer Schutthalde im Tal des rivière à Pierre, Gaspé Halbinsel, in den letzten zwei Jahrhunderten rekonstruieren. Die dendroökologischen Daten ließen erkennen, daß die obere Grenze des Waldes gegen Ende des 19. Jahrhunderts tiefer lag als die gengenwärtige Grenze, daß die Wald-Vegetation bis in die Mitte des 20. Jahrhunderts eine Ausdehnung erfuhr, wenn auch gewisse Anzeichen der Instabilität ab dem Ende des 19. Jahrhunderts aufgetreten sind. Der Waldrand ist auf seine gegenwärtige Position nach den fünfziger Jahren zurückgewichen. Die mit dendrogeomorphologischen Methoden errechnete durchschnittliche jährliche Sedimentierungs-Rate betrug während der zweiten Hälfte des 19. Jahrhunderts unter 0,1 cm und erreichte anschließend 0,5 cm/Jahr, nach 1975 dann über 1,0 cm/Jahr. Die verstärkte Aktivität am Hang geht wohl auf ein häufigeres Auftreten vereister Block- ströme zurück