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The influence of vegetation and microtopography on fine-scale variability of thaw depth is largely unknown but potentially important for improving modeling of ecosystem-permafrost interactions. To elucidate their influence, we measured tree density, shrub cover and cryptogam presence (lichen and bryophyte) on forested permafrost peat plateaus in the discontinuous permafrost zone in the southern Northwest Territories, Canada. Greater tree density was associated with shallower thaw depth (approximately one quarter of the variance), whereas shrub cover had a negligible influence on thaw depth. Cryptogam species influenced thaw depth, with greater thaw depth associated with Sphagnum than with Cladonia (a difference on the order of 10%). Greater thaw depth occurred beneath hummocks than beneath hollows (a difference also on the order of 10%). Together, canopy cover, cryptogam species and microforms contribute to a variation of roughly half the variance in thaw depth in the peat plateau landscape.

La présence de la naïade grêle, Najas gracillima (Najadaceae), dans la flore aquatique indigène du Québec est confirmée. Cette espèce sensible à la pollution est en déclin dans toute son aire naturelle nord-américaine en raison de l’eutrophisation des lacs et des cours d’eau. Pour faciliter l’identification de cette rareté, une clé des Najas de la province et une discussion des caractères permettant l’identification du Najas gracillima sont incluses. Le danger de nuire au Najas gracillima en le confondant avec l’exotique et envahissant Najas minor est souligné. De plus, nous présentons les données les plus à jour sur la répartition et l’écologie du Najas gracillima dans le monde et en Amérique du Nord, ainsi qu’une carte de répartition de l’espèce dans l’est du Canada et les territoires adjacents, basée sur un inventaire exhaustif de la littérature et des spécimens de l’Herbier national du Canada (CAN), de l’Herbier des plantes vasculaires d’Agriculture et Agroalimentaire Canada (DAO) et de l’Herbier Marie-Victorin (MT). Nous ajoutons des notes détaillées sur le site de la seule population connue du Québec.The presence of the thread-like naiad, Najas gracillima (Najadaceae), in the indigenous aquatic flora of Québec (Canada) is confirmed. This species is highly sensitive to pollution and, due to the eutrophication of lakes and streams, is in decline throughout its natural range in North America. To facilitate the identification of this rare species, the present article provides a key to the species of Najas occurring in Québec, along with a discussion of the distinguishing characteristics of N. gracillima. The danger of confusing this species with the exotic and invasive N. minor is also highlighted. In addition, the present article provides up-to-date global distribution data for N. gracillima, and a distribution map for the species in eastern Canada and the adjacent United States, based on an exhaustive survey of the literature and of specimens in the National Herbarium of Canada (CAN), the Agriculture and Agri-Food Canada Collection of Vascular Plants (DAO), and the Marie-Victorin Herbarium (MT). Detailed notes on the habitat of the only known location for this species in Québec are also included

During summer 2015, 192 samples of foliage were taken from 13 different Prunus species found mostly along the Ottawa River (Quebec, Ontario; 148 samples) and in the Vineland region (Ontario; 44 samples). A total of 39 mites species were collected, representing 9 families and 25 genera. Out of 39 species, 20 were strictly phytophagous and 19 were predators. Estimators of the true species diversity indicated that most of the mite fauna associated with the foliage of those Prunus species in the areas sampled was captured. One eriophyid mite species appears to represent a new species for science. In terms of host range, phytoseiids appear to be less specific than eriophyoids and both taxa can exhibit host preferences. Eriophyoid mites were not so host specific inside the genus Prunus, although they may be restricted to the genus. Tetranychoid mites were generalist. Three species of Eriophyidae were found within galls on Prunus leaves: Eriophyes cerasicrumena, E. emarginatae and E. prunidemissae.In addition to providing an overview of the mite fauna of Prunus foliage and galls, this project provides two identification keys to the eriophyid mite species associated with galls, one based on the mite morphology, and the other based on the morphology of the galls. .