Forked Three-awned Grass, Aristida basiramea Engelm. ex Vasey : a new addition to the flora of Quebec

A population of Forked Three-awned Grass (Aristida basiramea Engelm. ex Vasey; Poaceae) was found for the first time in Quebec, on a sand barren of the Cazaville region (Haut-Saint-Laurent). The only other region where this species is known in Canada is on the southern side of Georgian Bay in Ontario.Une population d’Aristida basiramea Engelm. ex Vasey (Poaceae) fut trouvée pour la première fois au Québec, dans une lande sableuse de la région de Cazaville (Haut-Saint-Laurent). Le seul autre endroit où l'espèce est présente au Canada est sur le côté sud de la Baie Géorgienne en Ontario

La vallée laurentienne au XVIIIe siècle : un paysage à connaître

Cette note de recherche vise à montrer que le paysage de la vallée laurentienne au XVIIIe siècle est complexe et varié. L'aménagement de l'espace seigneurial révèle des disparités considérables qui s'expliquent par divers facteurs intervenant à des échelles différentes. L'exploitation d'une série documentaire uniforme, comme les aveux et dénombrements du Régime français, pourrait constituer une voie de recherche utile pour dégager les phénomènes qui influencent la constitution du paysage rural.This research note attempts to show that the landscape of the Laurentian Valley in the XVIIIth century was complex and varied. Organization of seigneurial space reveals major disparities, explainable by the interplay of diverse factors at different levels. Use of a single uniform mode of documentation, such as the « aveux et denombrements » of the French regime, could be an important avenue of research for discovering the phenomena which influenced the formation of the rural landscape

Effect of Climatic Fluctuations on Post-Fire Regeneration of Two Jack Pine and Red Pine Populations during the Twentieth Century

The age structure of two mixed red pine (Pinus resinosa Ait.) and jack pine (Pinus banksiana Lamb.) forests located at Lac Duparquet, northwestern Québec, were correlated with mean annual temperature and total precipitation recorded at Iroquois Falls for the period between 1913 and 1986. The age structures of both pine species showed a common pattern of regeneration characterized by low regeneration before 1930, an important regeneration peak starting around the 1930s, a dip in the age structure around 1950, a second, though less important, regeneration peak in the 1960s, and an important drop, especially for red pine, after 1970. In general, high regeneration rates were positively correlated with precipitation and negatively with temperature, suggesting that pine recruitment is negatively affected by low snow cover and/or drought. The absence of correlation with temperature suggests that the red pine northern limit may be controlled more by a change in the fire regime than by increasing temperature.Les structures d'âge des populations de pin rouge et de pin gris, échantillonnés dans deux sites du lac Duparquet (Abitibi), ont été corrélées avec la moyenne annuelle des températures et les précipitations annuelles enregistrées à Iroquois Falls, entre 1913 et 1986. Les structures d'âge montrent un patron commun caractérisé par une régénération faible avant 1930, un pic de régénération débutant au cours des années 30, une baisse importante autour de 1950, un second pic de régénération, quoique de moindre importance, dans les années 60 et une décroissance importante après 1970. L'abondance de la régénération est généralement positivement corrélée avec les précipitations et négativement corrélée avec la température, indiquant ainsi que le recrutement des individus serait négativement influencé par une couverture nivale faible ou une sécheresse prolongée. L'absence d'une corrélation positive avec la température indique que la limite nord du pin rouge serait déterminée par un changement dans le régime des feux et non par une baisse des températures.Die Altersstrukturen von zwei Wàldern mit Rotkiefer (Pinus resinosa Ait.) und Graukiefer (Pinus banksiana Lamb.) am See Duparquet, nordwestliches Québec, wurden mit der durchschnittlichen Jahrestemperatur und den gesamten gemessenen Niederschlâgen an den Iroquois Falls fur die Zeit zwischen 1913 und 1986 in Beziehung gebracht. Die Altersstrukturen beider Kiefernarten wiesen ein gemeinsames Muster der Regenerierung auf, charakterisiert durch eine niedrige Regenierung vor 1930, einen bedeutenden Regenerierungshohepunkt, der in den 30er Jahren beginnt, ein Sinken der Altersstruktur um 1950, einen zweiten, wenn auch weniger bedeutenden Regenerierungshohepunkt in den 60er Jahren und einen bedeutenden Rùckfall, besonders der Rotkiefer, nach 1970. Im allgemeinen wurden hone Regenerierungsraten positiv mit Niederschlâgen und negativ mit Temperatur in Beziehung gebracht, so dass man annehmen kann, dass die Zunahme von Kiefern durch eine niedrige Schneedecke und/oder Trockenheit negativ beeinflusst wird. Das Fehlen einer welchselseitigen Beziehung zur Temperatur lâsst annehmen, dass die nôrdliche Grenze der Rotkiefer eher durch einen Wechsel im Vorkommen von Brànden als durch ansteigende Temperaturen kontrolliert wird

The history and tree stratum of an old-growth forest of Haut-Saint-Laurent region, Quebec

An old-growth forest of presettlement origin was recently discovered at the northern limit of the Eastern Deciduous Forest (sensu Braun 1950) of North America, in an area that is extensively affected by logging, land clearing, and agriculture. In a study of the disturbance history, forest composition, and dynamics of this old-growth forest, we found that (1) the preservation of the forest can be attributed to the initial settler’s lack of interest in exploiting it and to a strong sense of conservation by his descendants; (2) an American elm-black ash (Ultnus americana L.-Fraxinus nigra Marsh.) community occupies more hydric sites(approximately 15% ofthe forest) and a sugar maple -American beech (Acer saccharum Marsh.-Ftzgws grandifolia Ehrh.) community occurs on mesic sites; (3) larger canopy trees range in age from 150 to 300 years; (4) despite the absence of any major perturbation in the mesic portion of the site, the composition is not in equilibrium and beech is apparently increasing in abundance over the presently dominating maple; (5) the average tree growth has been very slow compared to that of trees in adjacent disturbed forests. Ecological information obtained from old-growth forests can contribute to decision making in management of natural areas

Effect of a major ice storm on understory light conditions in an old-growth Acer-Fagus forest: Pattern of recovery over seven years

We evaluated the effects of a major ice storm on understory light conditions (%PPFD, photosynthetic photon flux density) in an old-growth Acer-Fagus forest in Quebec, based on pre- and post-disturbance light measurements taken until the seventh growing season after the event (which occurred in January 1998). Before the ice storm, most microsites received between 2 and 4%PPFD. Following the ice storm, the stand-level mean %PPFD increased four- to five-fold, ranging from 13.8 to 20.5%PPFD, from 0.3 to 4 m aboveground. Despite its magnitude, the post-ice storm increase in light transmission was short-lived. By 1999 (2-year+), the mean light levels had decreased by half, and recovery to pre-storm conditions occurred within 3-7 years, depending on height. The decrease in light transmission during the post-disturbance years followed an inverse J-shape trend, indicating more dynamic changes early after disturbance. By 2004 (7-year+), light levels at ≤2 m had become slightly but significantly lower than before the ice storm, with most microsites receiving <2%PPFD. The ice storm led to a synchronized increase of the light levels at almost all understory locations, which might allow a high proportion of the advanced regeneration to experience a release. However, due to the rapid recovery of the light conditions to levels similar or lower than before the ice storm, this disturbance should be more advantageous to shade-tolerant species

Selecting herbaceous plant cover to control tree invasion in rights-of-way

Ce texte est issu d’un symposium: International Symposium on Environmental Concerns in Rights-of-Way Management (7e : 2000 : Calgary, Alberta)©ElsevierFollowing construction of a right-of-way, environmental regulation often requires the rapid restoration of a herbaceous plant cover to control erosion and/or attenuate visual impact. Herbaceous species can be selected with the added long-term goal of inhibiting tree invasion. We present a review of empirical evidence that can guide species selection. This review is based on an extensive survey and critical evaluation of relevant North American studies published in scientific papers, technical reports, and conference proceedings. Vegetation managers and scientists were also consulted for up-to-date information on on-going experiments. Observational and experimental evidence of inhibition in both natural and managed communities confirm that the biological control approach has significant potential. However, scientific evaluation of the long-term inhibition capacity of seeding mixtures is still rare. Ecological mechanisms favoring competitive ability are not always well understood but involve the sequestration of available resources and the modification of environmental conditions. Two approaches characterized experimental inhibition studies in rights-of-way. The first aims to test the interference potential of commercially available species commonly used in restoration, while the second favors the establishment of wild communities. Both approaches have their advantages and limitations, but several studies show that the establishment phase is crucial. Knowledge is lacking especially for the establishment of wild species. This review allowed us to identify 66 herbaceous species based on a critical assessment of the evidence provided. Besides inhibition potential, factors such as species availability and possible nuisance should also be considered

Effect of a major canopy disturbance on the coexistence of Acer saccharum and Fagus grandifolia in the understorey of an old-growth forest

In forest communities, species coexistence can be favoured by disturbance-related variations in light regime coupled with rank reversal in species performance. The objective of this study was to determine if a major canopy disturbance, resulting from an ice storm, would favour the coexistence of sugar maple (Acer saccharum) and beech (Fagus grandifolia) in an old-growth forest located near the northern limit of the species' range. The growth, density and frequency of occurrence of understorey stems were evaluated 7 years after the ice storm and compared with pre-disturbance values to determine if sugar maple, a slightly less shade-tolerant species, would be favoured over beech. Although height and radial growth increased three- to five-fold, and > 70% of the 5-10 cm d.b.h. stems showed a release, sugar maple did not benefit more from the opening of the canopy than beech. The inability of sugar maple to outgrow beech might be related to the high proportion of beech root sprouts at our site, suggesting that the potential for the disturbancemediated mechanism to slow the competitive exclusion of maple might decrease as the importance of vegetative reproduction increases in beech. Prior to the disturbance, sugar maple was more abundant and occurred in a larger proportion of the plots among small size classes, while beech dominated in the larger size classes. Although some increases in the density of both species were detected after the disturbance, the general trends of relative abundance and distribution of the species were not modified significantly. Our results do not indicate that a single canopy disturbance such as the major 1998 ice storm significantly favoured sugar maple over beech. When a disturbance opens the canopy, competition for light in gaps may tend to maintain or reinforce a pre-existing hierarchy instead of reversing it, especially when interspecific differences in postdisturbance growth are small or absent, as in this study. This study shows that the dynamics of sugar maple - beech communities are more complex than previously envisaged and that revised models should incorporate additional factors (e.g. vegetative reproduction) that might also play an important role in regulating community dynamics

Homogeneous light in shade-house experiment overestimates carbon gains in Norway maple seedlings

We set up a shade-house experiment with Norway maple growing at two light intensities typical of a disturbed and undisturbed forest canopy from either a homogeneous or a dynamic regime that mimics sunflecks. We show that although horticultural-grade shade-cloths can be finely tuned to provide daily averages of any light intensity, they do not appropriately mimic natural forest understories which are characterized by dynamic light environments composed of intense but short direct light events interspaced with prolonged period of low diffuse light. The results suggest that replicating the dynamic light environment of forests could be very important in experiments aimed at identifying the traits responsible for invasiveness in exotic species in forest understories, such as Norway maple in North America