Personne : Pellerin, Stéphanie
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Université Laval. Département d'aménagement
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- PublicationAccès libreLa flore des tourbières de l’île d’Anticosti lorsque soustraite au broutement par le cerf de Virginie(2017-06-21) Poulin, Monique; Bachand, Marianne; Pellerin, Stéphanie; Côté, Steeve D.; Courchesne, MilèneDepuis son introduction, il y a plus d’une centaine d’années, le cerf de Virginie (Odocoileus virginianus Zimm.) a fortement perturbé la flore de l’île d’Anticosti. Les communautés forestières sont sans contredit celles qui ont été les plus affectées. Toutefois, le cerf exploite et perturbe aussi d’autres écosystèmes, comme les tourbières. Dans ce contexte, nous voulions savoir quelle serait la diversité végétale des tourbières à la suite du retrait du cerf. Pour ce faire, 53 exclos ont été mis en place en 2007 et suivis pendant 8 ans. Au total, 125 espèces végétales ont été identifiées dans l’ensemble des exclos en 2007 et 151 espèces après 8 ans d’exclusion du cerf, ce qui représente une hausse de 21 %. Le nombre d’espèces indicatrices, c’est-à-dire celles caractéristiques d’un habitat donné, a également augmenté, passant de 33 à 48, la hausse étant particulièrement importante dans les laggs (écotones entre la forêt et la tourbière). Le recouvrement des espèces préférées par le cerf a grandement augmenté, notamment celui du bouleau nain (Betula pumila L.) et de la sanguisorbe du Canada (Sanguisorba canadensis L.) (respectivement 2 et 8 fois). Au final, les tourbières de l’île d’Anticosti possèdent un potentiel de diversité végétale plus élevé qui peut s’exprimer avec l’arrêt du broutement par le cerf de Virginie.
- PublicationAccès libreNative plant turnover and limited exotic spread explain swamp biotic differentiation with urbanization(Uppsala, Sweden : Opulus Press, 2020-11-27) Paquin, Léo Janne; Bourgeois, Bérenger; Pellerin, Stéphanie; Didier Alard; Poulin, MoniqueQuestions: Does urbanization promote biotic differentiation or homogenization of swamp plant communities? What is the contribution of natives and exotics to swamp response to urbanization? Location: Quebec City, Canada. Methods: Plant communities of 34 swamps located in low, moderately or highly urbanized landscapes were sampled, and species classified into three exclusive groups: native wetland, native upland and exotic plants. Urbanization's influence on the richness of each plant group was assessed using mixed models. Between-site compositional similarities were calculated to identify variations in beta diversity with urbanization level using tests for homogeneity in multivariate dispersion. Beta diversity was further partitioned into species replacement and richness difference for each plant group. Finally, the relationships of ten environmental variables representing soil water saturation and microtopography with plant assemblages were determined by redundancy analysis. Results: Although the richness of exotics increased with urbanization intensity, revealing increasing propagule pressure, it remained six to 27 times lower compared to the richness of natives, which remained stable with urbanization. On the other hand, beta diversity increased with urbanization, with higher dissimilarities in species composition between highly urbanized swamps than between low-urbanized ones. This pattern resulted from high species replacement among natives, while richness difference mainly contributed to exotic beta diversity. Changes in plant assemblages were mostly associated with bryophyte cover and soil drainage and red mottle size, suggesting that hydrological conditions likely acted as a strong driver of swamp plant community response to urbanization. Conclusions: Swamp plant communities experienced biotic differentiation with increasing urbanization. This differentiation pattern likely was linked to the unpredict-able effect of urbanization on hydrological regimes, which promoted high native turnover while limiting exotic spread. Long-term monitoring is recommended to ensure that exotics do not outcompete natives through time. Designing sustainable cities requires a greater understanding of the multifaceted effect of urbanization on biodiversity.
- PublicationAccès libreEx situ germination as a method for seed viability assessment in a peatland orchid, Platanthera blephariglottis(Botanical Society of America by the Brooklyn Botanic Gardens, 2015-03-01) De Vriendt, Laurent; Poulin, Monique; Pellerin, Stéphanie; Lemay, Marc-AndréPREMISE OF THE STUDY: Assessing seed quality in orchids has been hindered by stringent germination requirements. Seed quality has traditionally been assessed in orchids using in vitro or in situ germination protocols or viability staining. However, these methods are not always well suited for rapid assessment of viability in the context of ecological studies. METHODS: The potential of an ex situ protocol for seed viability assessment of orchids in ecological studies was investigated by sowing seeds of Platanthera blephariglottis on Sphagnum moss collected in the orchid's natural habitat. Ex situ germination results were compared with those obtained by viability staining using triphenyltetrazolium chloride (TTC), and the effect of seed testa color on staining and germination results was investigated. KEY RESULTS: The ex situ protocol yielded high germination rates, with 66% of the seeds germinating after 9 wk. Depending on the seed testa color class, ex situ germination rates were about 1.4 to 2.5 times higher than viability rates determined using TTC, indicating that the TTC technique underestimated viability compared with the method using ex situ germination. The TTC estimates of viability rates were higher for seeds with dark-colored testae than for pale ones, whereas seed testa color had no effect on germination. CONCLUSIONS: Our study showed promising results for the use of ex situ germination as an alternative to previously developed protocols for seed viability assessment of orchids in ecological studies. Staining using TTC might not be well suited for this purpose, since it introduced a bias with respect to seed testa color.
- PublicationAccès libreThree decades of vegetation changes in peatlands isolated in an agricultural landscape(Blackwell Publishing, 2015-04-01) Pasquet, Salomé; Poulin, Monique; Pellerin, StéphanieQuestions : What vegetation changes occurred over three decades on two large temperate peatlands (1115 ha) isolated in an agricultural landscape and affected by a human-ignited fire? Location : Southwest Québec, Canada. Methods : In 2012, we revisited 103 plots first sampled in 1984–85. Changes in species composition were evaluated using the Sørensen dissimilarity index, in species frequency with Chi-square goodness-of-fit tests, and in species cover using one-sample t-tests. Tree encroachment was evaluated using aerial photographs and satellite imagery. We used linear discriminant analyses (LDA) and ANOVA to evaluate the impact of tree encroachment on species composition. Results : We found a floristic dissimilarity of 35% between 1984 and 1985 and 2012. Most species whose frequency and mean cover increased were peatland species, while most species with lower frequency and mean cover in 2012 were non-peatland species. The total area occupied by forest increased from 26% to 51%, an overall gain of 280 ha of forest. The species composition of old and new forests as well as of open sectors was highly distinct, as shown by the LDA that correctly assigned 97% of the sampling plots to these groups. Non-peatland species were 15 and five times more abundant than peatland species in old and new forests than open habitats, respectively. Conclusions : Gradual drying of the peatland margins due to drainage of the surrounding catchment, as well as post-fire succession are likely the main drivers of the changes observed. Overall, our study showed that peatlands isolated in an anthropogenic landscape are dynamic ecosystems where vegetation communities can experience substantial changes in a short time frame. The broader implication is that peatland conservation in highly modified landscapes must be linked to restoration.
- PublicationRestreintLong term effects of deer browsing and trampling on the vegetation of peatlands(ScienceDirect, 2005-11-15) Pellerin, Stéphanie; Côté, Steeve D.; Huot, JeanOverabundance of wild ungulates, especially exotic species, is a major threat to several ecosystems worldwide. While the response of forest vegetation to high density of herbivores has been well studied, far less is known about peatland vegetation. In this paper, we assessed the long term impact of white-tailed deer (Odocoileus virginianus) on plant communities of ombrotrophic (bog) and minerotrophic (fen) peatlands in eastern North America. Vegetation of five peatlands that have experienced high deer densities for at least 75 years was compared with that of five peatlands situated at proximity but on deer-free islands. We investigated deer impacts on plant species composition and cover, shrub height and cloudberry (Rubus chamaemorus) fruit/flower production and morphology. In bogs, white-tailed deer had no long-term impact on plant species assemblages, but reduced lichen cover and increased sedges and grasses cover as well as the surface area of bare peat. On the other hand, the floristic composition of fens differed significantly between sites where deer were present or absent. Plant diversity was greater in undisturbed fens than in disturbed fens, especially for shrubs, sedges and liverworts. No detrimental effects of browsing on shrub height were observed. Conversely, deer browsing seemed to have deleterious impacts on cloudberry fruit/flower production as well as on the number of leaves per individual. Overall, our results suggest that white-tailed deer had some important impacts on the vegetation of peatlands that could be harmful for the long-term conservation of peatland plant diversity.
- PublicationAccès libreSpecies indicators of ecosystem recovery after reducing large herbivore density : comparing taxa and testing species combinations(Elsevier Science Ireland, 2014-03-01) Brousseau, Pierre-Marc; Cloutier, Conrad; Poulin, Monique; Moretti, Marco; Cardinal, Étienne; De Cáceres, Miquel; Bachand, Marianne; Pellerin, Stéphanie; Côté, Steeve D.; Hébert, Christian; Martin, Jean-LouisIndicator species have been used successfully for estimating ecosystem integrity, but comparative studies for defining optimal taxonomic group remain scarce. Furthermore, species combinations may constitute more integrative tools than single species indicators, but case studies are needed to test their efficiency. We used Indicator Species Analysis, which statistically determines the association of species to one or several groups of sites, to obtain indicators of ecosystem recovery after various deer density reductions. We used five taxonomic groups: plants, carabid beetles, bees, moths and songbirds. To test whether species combinations could complement single indicator species, we used plants as a model taxon and examined the indicator value of joint occurrence of two or three plant species. Our study relies on experimental controlled browsing enclosures established for six years on Anticosti Island (Quebec). Four levels of deer density (0, 7.5 and 15 deer km-2 and natural densities between 27 and 56 deer km-2) were studied in two vegetation cover types (uncut forests and cut-over areas), in a full factorial design for a total of eight experimental treatments. For all taxa but bees, we tested 54 treatment groups consisting in one specific density or in a sequence of two or more consecutive deer densities in one or both cover types (ten groups for bees, sampled only in cut-over areas). We found 12 plants, 11 moths and one songbird to be single species indicators of ecosystem conditions obtained under 12 different treatment groups. Six treatment groups were indicated by plants and six different ones by moths, of which one group was also identified by a songbird species. Moths were thus worth the extra sampling effort, especially since the groups they indicated were more treatment-specific (mainly one or two deer density treatments). We tested the same 54 treatment groups for plant species combinations represented by two or three co-occurring species. Plant combinations efficiently complemented plant singletons for detecting ecosystem conditions obtained under various deer densities. In fact, although singletons were highly predictive, 17 additional treatment groups were identified exclusively with two- and three-species combinations, some being more treatment-specific. Our findings show that plants and moths provide complementary indicators of ecosystem conditions under various deer densities, and that computing species combinations increases our capacity to monitor ecosystem recovery after reducing herbivore densities.
- PublicationAccès libreCompositional and functional trajectories of herbaceous communities after deer density control in clear-cut boreal forests(Conseil national de recherches du Canada, 2015-02-17) Tremblay, Jean-Pierre; Poulin, Monique; Bachand, Marianne; Pellerin, Stéphanie; Côté, Steeve D.Overabundant populations of large herbivores have strong persistent effects on forest composition, structure, and function. However, the mechanism through which plant communities recover their original composition and function after herbivore management remains poorly understood. We assessed the temporal trajectories of the herbaceous communities in Abies balsamea (L.) Mill. and Picea glauca (Moench) Voss stands on Anticosti Island (Quebec, Canada) over 8 years following clear-cutting and deer management. The impact of deer exclusion or reduction to 7.5 and 15 deer·km–2 was compared with benchmark in situ deer densities (27 and 56 deer·km–2). Effects of deer management treatments on plant species and functional trait assemblages over time were assessed using principal response curves. Although complete deer exclusion seemed necessary to modify species composition from that occurring under intense browsing, a reduced density of 7.5 deer·km–2 was sufficient to induce significant changes in functional trait assemblages of regenerating stands. For instance, reduced deer densities favored plants with brightly colored flowers and compound inflorescences pollinated by animals and producing large seeds and fleshy fruits dispersed by animals. We conclude that the boreal forest's herbaceous communities are resilient to chronic browsing when deer population reduction and forest clearcutting are applied in synergy.
- PublicationAccès libreEnvironmental filtering and spatial processes in urban riparian forests(Blackwell Pub., 2016-06-13) Brice, Marie-Hélène; Poulin, Monique; Pellerin, StéphanieQuestions : What are the spatial processes structuring plant trait composition in urban riparian forest communities at different spatial scales? What are the relative roles of local conditions (including historical aspects), landscape context and spatial processes in the community assembly of these forests? Location : Montréal, Québec, Canada. Methods : Species plant composition was inventoried in 57 riparian forests located along a gradient of urbanization. To analyse plant communities in terms of their trait composition, community-weighted means were calculated using eight functional traits. Forests were characterized by local (physical features, hydrological regime and historical disturbances) and landscape (surrounding land use) variables. Spatial processes structuring communities were assessed using Moran's eigenvector maps and asymmetric eigenvector maps. The relative importance of these three subsets (local, landscape and spatial variables) on tree, shrub and herb functional composition was quantified by variation partitioning using redundancy analyses. Results : Functional patterns in riparian forests resulted primarily from environmental filtering (local and landscape variables). Local conditions, especially flood intensity, exerted an overriding selection pressure on functional composition of riparian plant communities. Urbanization seemed to act indirectly on trait patterns through the alteration of hydrological disturbances caused by on-going and historical land transformation. Nevertheless, dispersal along rivers was also a significant structuring force, while overland dispersal was negligible. Conclusions : Our study highlights that under severe natural disturbance regimes, the effect of natural filters outweighed the negative effects of urban filters. However, the alteration of natural flooding processes by human activities is also a major mechanism influencing plant trait composition in urban riparian communities as forests subjected to reduced flooding intensity experienced a greater effect of urbanization. The effects of urbanization and of past land uses on plant communities were greater for trees than for shrubs and herbs due to the high turnover rate of the latter. Finally, our results showed the importance of dispersal along rivers for biodiversity even in fragmented urban landscapes.