La végétation riveraine du lac à l’Eau Claire, Québec subarctique

Abstract

Les platières sont des tabliers organo-minéraux occupant la rive de plusieurs grands lacs de la toundra forestière du Québec. La végétation qu'elles portent est périodiquement affectée par l'activité des vagues et les poussées glacielles. Le maintien de ces végétaux dans des habitats hautement dynamiques soulève plusieurs questions d'intérêt écologique et géomorphologique qui ont été étudiées au lac à l'Eau Claire, en Hudsonie. Les platières comportent une mosaïque de parcelles végétales en voie de régression ou de croissance, selon l'exposition aux perturbations allogènes. Bien qu'il existe un étagement des espèces en fonction du gradient d'immersion et d'exposition, la zonation en bandes subparallèles à la rive habituellement observée en périphérie des lacs tempérés, est ici peu prononcée. On trouve la diversité floristique optimale dans des sites présentant des conditions intermédiaires d'exposition où le bilan sédimentaire est très variable. Le développement des platières en région subarctique est stimulé par des fluctuations très irrégulières du niveau lacustre d'une année à l'autre, probablement en réponse aux variations interannuelles des précipitations de neige. La dénivellation du plan d'eau au cours de la saison de végétation influence l'intensité de l'activité géomorphologique des glaces et des vagues sur les rives et détermine ainsi les modalités de la succession écologique.Around most large lakes of the forest tundra zone in Québec, vegetation colonizes sheltered shores periodically affected by storm waves and ice pushes. Many questions of ecological and geomorphological interest arise from the existence of these vegetation forms within particularly dynamic habitats. In the Lac à l'Eau Claire area, vegetated platforms comprise a mosaic of regressive and progressive mats, resulting from exposure to varying degrees of geomorphic disturbance and prolonged drowning. The species occupy different vertical positions according to immersion and exposure gradients, but zonation patterns parallel to the shoreline, typical of other regions are uncommon here. Species richness is highest in intermediate disturbance conditions, that is along shores where the sedimentary environment is most unstable. Water level during growth period controls the position reached by ice-pushes and waves along the shores and affect the plant succession process. Water level changes from year to year are probably caused by annual variations in snow fall amounts.Am Ufer von mehreren grossen Seen der Wald-Tundra Québecs befinden sich organisch-mineralische Plattformen. Ihre Vegetation wird durch die Aktivitat der Wellen und die Eisschiibe periodisch gestôrt. Das Bestehen dieser Vegetation an einem hôchst dynamischen Standort wirft mehrere ôkologische und geomorphologische Fragen auf, die am Lac à l'Eau Claire, Hudson Bay, ùberprûft wurden. Die Plattformen bestehen aus einem Mosaik von Vegetations-Parzellen, die sich zuruckentwickeln Oder entwickeln, je nachdem welchen Storungen von aussen sie ausgesetzt sind. Obwohl die Arten je nach Gefâ...

Using ice‐scars as indicators of exposure to physical lakeshore disturbances, Corvette Lake, northern Québec, Canada

“…There are 13 pebble and boulder pavement sections all distributed on gently sloping shores usually located in straight portion of the shoreline. This type of shore is characterized by organo‐mineral accumulations stabilized by lakeshore vegetation and forming vegetated platforms (Bégin and Payette, ). From a morpho‐sedimentological point of view, the pavement sections can be divided into two subtypes, based mainly on their ruggedness: (1) uniform pavements without boulders and wave‐breakers and (2) pavements with large boulders, which increase the ruggedness of the shore.…”

“…Shoreline segmentation is a method currently used in environments such as lakes (Laverdière and Guimont, ; Bégin, ) and seacoasts (Berry et al , ; Finlayson and Shipman, ; Finlayson, ). The first steps of this method are to produce a map based on field observation of the main physical features structuring the shore (which are difficult to detect on aerial photographs) and to divide the shoreline according to these features and other permanent variables such as the orientation of the shore.…”

“…Shores are interface systems mainly structured by hydrodynamic disturbances, which are defined by their nature, intensity, frequency, duration, and spatial extent (Kimmerer and Allen, ; Keddy, ; Sousa, ). Several studies have focused on the structural role of disturbances on shoreline vegetation at a local scale, such as on rocky coastal shores (Dayton, ; Lubchenco and Menge, ; Sousa, ; Lubchenco, ; Zacharias and Roff, ), river floodplains (Bell and Moral, ; Kimmerer and Allen, ; Nilsson and Holmström, ; Harris, ; Nilsson, ; Ward and Tockner, ), and lacustrine non‐ligneous plants (Spence, ; Wassen, ; Auclair et al , ; Jupp and Spence, ; Keddy, , ; Nilsson and Holmström, ; Wilson and Keddy, ; Duarte and Kalff, ; Chambers, ; Bégin and Payette, ; Coops et al , ; Denneler et al , ; Riis and Hawes, , ).…”

“…However, there are physical processes other than waves that can play a significant role in the lakeshore disturbance regime. For instance, in northern regions, ice action can have a significant influence on the shoreline physical configuration (Alestalo, ; Bégin, ; Dionne, , ). Boulder ridges, wave breakers, boulder and pebble pavements on gently sloping shores, microtopographic features on sandy beaches, and ice‐scars on lakeshore trees are all geomorphological features associated with ice activity (Dionne, , ).…”

“…Ice action features in northern lakes are mainly caused by the influence of wind on ice sheet movements during the spring flood, when ice cover begins to melt on the edge and lake levels are high due to snow melt (Dionne, ). Ice floods can produce significant mechanical damage to lakeshore vegetation, such as shrub trimming (Payette, ; Bégin and Payette, , ; Bégin and Filion, ) and ice‐scars (Alestalo, ; Dionne, , ; Payette, ; Bégin, ; Tardif and Bergeron, ). Ice‐scars provide a precise record of annual ice‐push events (Alestalo, ; Alestalo and Häikiö, ; Schweingruber, ; Bégin, ) and have been successfully used in previous studies to reconstruct ice‐flood history in many northern lakes (Bégin and Payette, ; Lepage and Bégin, ; Tardif and Bergeron, ; Bégin, , ; Lemay and Bégin, ).…”