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Studies have reported divergent results on the effect of soil fertility and canopy opening on understory density and growth of sugar maple (AS; Acer saccharum Marsh.) and American beech (FG; Fagus grandifolia Ehrh.). The main objective of this study was to evaluate the effect of a gradient of canopy opening and soil fertility on the density and growth of AS and FG saplings in southwestern Quebec, Canada. We investigated 56 stands containing both AS and FG that were subjected to different disturbance history types (DHTs) (UF, unmanaged forest; PC, partial cut; and CC, clearcut) on various soil types. AS and FG absolute and relative sapling density varied greatly among the 56 stands; however, no significant effects of DHT, soil nutrient availability, or their interaction were found. Both species responded positively in terms of radial growth to canopy openings, with FG growth being slightly better than AS growth in PC stands compared with other canopy treatments. Contrary to our hypothesis, AS did not show significantly higher growth than FG following clear-cutting. These results do not support the idea that AS abundance and growth could be promoted by increasing the intensity of the canopy opening during harvest, at least on the generally acidic and base-poor soils that were investigated. Key words: Fagus grandifolia, Acer saccharum, soil nutrient availability, light availability, saplings, clearcut, partial cut. Des etudes font etat de resultats divergents concernant l'effet de la fertilite du sol et de l'ouverture du couvert forestier sur la densite et la croissance de l'erable a sucre (AS; Acer saccharum Marsh.) et du hetre d'Amerique (FG; Fagus grandifolia Ehrh.) sous couvert. L'objectif principal de cette etude etait d'evaluer l'effet d'un gradient d'ouverture du couvert forestier et de la fertilite du sol sur la densite et la croissance des gaules d'AS et de FG dans le sud-ouest du Quebec, au Canada. Nous avons echantillonne 56 peuplements contenant des AS et des FG ayant ete soumis a differents types d'historique de perturbation (THP) (FN, forets non amenagees; CP, coupes partielles; CT, coupes totales) sur differents types de sol. La variation des densites absolue et relative des gaules d'AS et de FG entre les 56 peuplements etait importante, mais nous n'avons trouve aucun effet significatif du THP, de la disponibilite des nutriments du sol ou de leur interaction. La croissance radiale des deux especes a reagi positivement a l'ouverture du couvert, mais la croissance de FG etait legerement superieure a celle d'AS dans les CP comparativement aux autres traitements du couvert forestier. Contrairement a notre hypothese, la croissance d'AS n'etait pas significativement plus grande que celle de FG a la suite d'une CT. Ces resultats n'appuient pas l'idee qu'on puisse favoriser l'abondance et la croissance d'AS en augmentant l'intensite des ouvertures par la coupe, a tout le moins sur les sols generalement acides et pauvres en bases qui ont ete etudies. [Traduit par la Redaction] Mots-cles: Fagus grandifolia, Acer saccharum, disponibilite des nutriments du sol, disponibilite de la lumiere, gaules, coupe totale, coupe partielle., Introduction Throughout the last century, forest management has changed the structure and composition of temperate deciduous stands within the forested landscapes of Quebec. Most notably, results from several experiments have [...]

The effects of the permanent removal of the canopy-forming alga Fucus serratus was studied in terms of both functioning and diversity on a mid-low rocky shore ecosystem in the south-west English Channel (48°N 43.686', 3°W 59.282'). Ecosystem functioning was examined as net or gross primary productivity (NPP or GPP) and respiration (Resp) measured through C[O.sub.2] fluxes. Diversity was examined as number and composition of species. Measurements were performed in situ, during emersion times, without altering target assemblages. The experiment was designed with two treatments [control (C) or canopy removed (CR)] and five replicates, and was conducted over an 18-month period (from February 2006 to August 2007) to integrate the seasonal variability. The mean GPP and Resp were severely reduced in CR treatment compared to control throughout the survey. The mean NPP was not affected at first, due to the development of opportunistic green algae, but was drastically reduced after 9 months of experiment. The canopy removal affected neither the number of species nor their distribution among trophic groups, and the algal community was only slightly affected. The abundance and biomass of mobile invertebrates, however, were greatly reduced in the absence of canopy. This indicates an important effect of the dominant alga on the higher trophic levels of the community. At this tidal level, the canopy did not seem to affect the community by dampening the environmental stress but by providing food, habitat or both., Introduction Canopy-forming algae are often found in high biomass and abundance on rocky shores and may be responsible for the major part of carbon fluxes in these systems as they [...]

Canopy-forming seaweeds are important foundation species or ecosystem engineers in intertidal habitats. By limiting a variety of abiotic stresses during low tides, algal canopies improve the performance of many understory organisms. The reduction of heat stress through substrate shading and moisture retention has received considerable attention in marine biology. However, the thermal influence of canopies during winter has not been empirically evaluated. Using intertidal fucoid canopies (Ascophyllum nodosum) from Atlantic Canada, we did a field experiment contrasting canopy-covered and no-canopy areas to test the hypothesis that canopies limit low temperatures during winter low tides. During 35 days between January and March, mid-intertidal temperature was often negative near the time of the lowest daily tides, on average more than 1 °C lower on bare substrate than under full canopy cover. The difference between both canopy treatments was higher around spring tides than around neap tides. Temperature on bare substrate was once even up to 10 °C lower than under a full canopy. Previous studies have shown that single occurrences of lethal negative temperatures and frequent occurrences of sublethal temperatures kill intertidal organisms every winter. Thus, our study suggests that, in addition to their bioprotective role during summer, canopy-forming seaweeds might also play a relevant facilitative role during winter., Author(s): Ricardo A. Scrosati [sup.1] , Julius A. Ellrich [sup.1] Author Affiliations: (Aff1) 0000 0004 1936 7363, grid.264060.6, Department of Biology, St. Francis Xavier University, , B2G 2W5, Antigonish, NS, [...]