Stéphanie Pellerin

Peatland restoration in southern Québec (Canada): A paleoecological perspective>

Abstract We used macrofossil analyses to reconstruct the long-term development of plant assemblages and the history of fire events in a bog in southern Québec which was partly disturbed by peat mining activities and recently restored. Our main objectives were to (i) determine to what extent the present-day plant assemblage of an unmined sector of the bog resembles the plant assemblages that have been reconstructed for different periods of the ecosystem’s development, (ii) establish the frequency of fire events and their impacts on plant assemblages, and (iii) interpret the results from the restoration experiment by considering the natural development of the peatland over recent millennia. Throughout the ombrotrophic stage of the peatland’s development, plant assemblages have been stable and do not seem to differ strongly from those observed today in the unmined sector of the bog. Consequently, the present-day plant assemblage of the unmined sector could be considered a good reference to evaluate the restoration success of the mined area. The bog landscape was characterized by significant tree cover dominated by black spruce for almost its entire period of development. Consequently, a restoration experiment resulting in Sphagnum-dominated vegetation with a dense black spruce cover in the near future should not be considered a failure. Macrofossil analyses suggest that postfire vegetation succession occurring in the study site and elsewhere is similar to that resulting from restoration experiments conducted in eastern Canadian bogs. In both cases, the input of nutrients (biomass burning or artificial fertilization) strongly stimulates the growth of Polytrichum strictum colonies, which are rapidly overgrown by Sphagnum colonies in burned bogs. Therefore, it is possible that the restoration method used in eastern Canada will result in rapid vegetation succession culminating in a Sphagnum-dominated peatland. This case study shows that a detailed reconstruction of the history of a site is a valuable tool for clearly establishing the goals of a restoration program.

Recent expansion of jack pine in peatlands of southeastern Québec: A paleoecological study

Abstract Jack pine (Pinus banksiana) colonization and expansion in ombrotrophic peatlands of the Bas-Saint-Laurent region, southeastern Québec, was analyzed using macrofossil and dendrochronological analyses. During the last 80 years, and mainly between 1920 and 1945, several open peatlands dominated by Sphagnum species were invaded by jack pine following a fire event. This phenomenon appears to have no precedent over the last 8,900 years, at least in one of the study sites. Fires triggered the expansion by eliminating the Sphagnum mat and spreading thousands of pine seeds released by a few individuals. While fires contributed to the expansion of pines in bogs, this phenomenon may have been facilitated by a drier-than-average climatic period during the first part of the 20th century. The fact that dense jack pine stands are now growing on thick organic deposits indicates that this species has a wider ecological tolerance than previously known and/or that the Bas-Saint-Laurent peatlands have recently undergone major ecological and hydrological changes favouring the growth of non-bog species.

The Relative Impact of Human Disturbances on the Vegetation of a Large Wetland Complex

Anthropogenic disturbances are important factors structuring the vegetation of ecosystems, but their influence on peatlands remain poorly understood. We quantified the relative influence of anthropogenic disturbances, abiotic variables and spatial patterns on the floristic composition of a large wetland complex, and assessed the relationship between disturbances and species richness. Vegetation and abiotic data were collected in 253 plots, and disturbances determined using aerial photographs. Data were analyzed with multivariate and nonparametric techniques. Disturbances had detrimental effects on bryophyte and on true peatland species richness, but favored the richness of grass as well as non-peatland and exotic species. However, abiotic conditions are still predominant in controlling the overall plant composition at the complex level (25.2% of floristic variations explained, compared to 8.2% for disturbances). The vegetation heterogeneity was also mainly attributed to abiotic factors when taking account only fen habitats. The three sets of explanatory factors were equally important in structuring the vegetation of bog habitats. However, the most influential variables were those related to human activities. Our landscape ecology approach to study wetland vegetation allowed us to show that while human disturbances are important in structuring vegetation in bogs and fens, they do not override the prevalence of local abiotic conditions.

Environmental factors explaining the vegetation patterns in a temperate peatland

Although ombrotrophic temperate peatlands are important ecosystems for maintaining biodiversity in eastern North America, the environmental factors influencing their flora are only partly understood. The relationships between plant species distribution and environmental factors were thus studied within the oldest temperate peatland of Québec. Plant assemblages were identified by cluster analysis while CCA was used to related vegetation gradients to environmental factors. Five assemblages were identified; three typical of open bog and two characterized by more minerotrophic vegetation. Thicker peat deposit was encounter underlying the bog assemblages while higher water table level and percentage of free surface water distinguished the minerotrophic assemblages. Overall, the floristic patterns observed were spatially structured along the margins and the expanse. The most important environmental factors explaining this spatial gradient were the percentage of free surface water and the highest water-table level.

Fires in temperate peatlands (southern Quebec): past and recent trends

In this study, we reconstructed the long-term fire history of a set of ombrotrophic peatlands (bogs) located in a temperate region of southern Quebec (Bas-Saint-Laurent). Past and recent fire-free intervals (time interval between two consecutive fires) were compared using macrofossil analyses. During most of the Holocene epoch, fires were relatively rare events in bogs of the Bas-Saint-Laurent region. The fire-free intervals were approximately ten times longer (all sites considered) before the beginning of agricultural activities in the region (1800 AD) than after. This strongly suggests an anthropogenic influence on the fire regime prevailing in the bogs over the last 200 years. However, the shortening of the fire-free intervals was mainly the result of the ignition of one or two fires in almost every site during a relatively short pe- riod (200 years), rather than a higher fire frequency in each of the bogs. In some cases, fires had an influence on the vege- tation structure of bogs, but it is more likely that a combination of several disturbances (fire, drainage, and drier than average summers) favoured the establishment of dense stands of pine and spruce, a forest expansion phenomenon that is now widespread in temperate bogs.

Clearcutting and Deer Browsing Intensity Interact in Controlling Nitrification Rates in Forest Floor

Abstract: Major forest disturbance such as clearcutting may increase nitrification rates in the forest floor, but the magnitude of this NO3- flush varies among different forest ecosystems. Here, we tested the hypothesis that this variation could partly be due to differences in deer-browsing intensity. More specifically, we hypothesized that nitrification rates would decrease as deer browsing increased and that this effect would be higher in clearcuts than in forests. Our experimental design consisted of 3 replicated blocks, each consisting of 3 plots (10–40 ha) in which white-tailed deer densities were kept at 0, 7.5, and 15 individuals.km-2 for 6 y and a fourth plot in which natural deer densities varied between 27 and 56 deer.km-2. In the first year, 70% of mature balsam fir (Abies balsamea) forests in each plot were clearcut harvested. Average potential nitrification in forest floor samples was higher in clearcut than in forest plots. In clearcut plots, potential nitrification at the high deer density was about 2.5 times higher than at lower deer densities, thereby contradicting our first hypothesis. In forest plots, potential nitrification was negatively related to indices of soil available C but was unrelated to deer density. The shrub and herb vegetation in clearcut plots was dissimilar to, and more altered by, deer browsing than the understory vegetation in forest plots. In clearcut plots, increasing deer density reduced the percent cover of nitrophilous herbaceous species and increased the percent cover of graminoid plants. Possible mechanisms that could explain the interaction between forest disturbance and deer browsing intensity in controlling the magnitude of the NO3- flush are (1) soil N inputs via feces and urine, (2) loss of soil NO3- sinks due to the disappearance of nitrophilous plant species, and (3) browser-induced succession towards rangeland plant communities that stimulate rhizodeposition and soil N dynamics. Nomenclature: Gleason & Cronquist, 1991.

Functional Responses and Resilience of Boreal Forest Ecosystem after Reduction of Deer Density

The functional trait-based approach is increasingly used to predict responses of ecological communities to disturbances, but most studies target a single taxonomic group. Here, we assessed the resilience of a forest ecosystem to an overabundant herbivore population by assessing changes in 19 functional traits for plant, 13 traits for ground beetle and 16 traits for songbird communities after six years of controlled browsing on Anticosti Island (Quebec, Canada). Our results indicated that plants were more responsive to 6 years of reduced browsing pressure than ground beetles and songbirds. However, co-inertia analysis revealed that ground beetle communities responded in a similar way than plant communities with stronger relationships between plant and ground beetle traits at reduced deer density, a pattern not detected between plant and songbird. High deer density favored plants species that reproduce vegetatively and with abiotic pollination and seed dispersal, traits implying little interaction with animal. On the other hand, traits found at reduced deer density mostly involved trophic interaction. For example, plants in this treatment had fleshy fruits and large seeds dispersed by birds or other animals whereas ground beetle species were carnivorous. Overall, our results suggest that plant communities recovered some functional components to overabundant herbivore populations, since most traits associated with undisturbed forests were reestablished after six years of deer reduction. The re-establishment of functional plant communities with traits involving trophic interaction induces changes in the ground-beetle trait community, but forest structure remains likely insufficiently heterogeneous to shift the songbird trait community within six years.

Ex situ germination as a method for seed viability assessment in a peatland orchid, Platanthera blephariglottis.

UNLABELLED • PREMISE 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 orchids 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.

Factors Associated with the Presence of Flowering Individuals of Arethusa bulbosa (Orchidaceae) in Peatlands of Southern Quebec

Abstract: Arethusa bulbosa is a northeastern North American orchid species rare in most of its range. This study sought to determine the factors associated with the presence of Arethusa within peatlands and its absence from a priori suitable sites. Twenty-four plots with Arethusa were compared with paired plots from which the species was absent and with 22 plots in peatland where the species has never been present. Vegetation and abiotic variables were recorded within the plots, and anthropogenic variables were identified using aerial photographs. The IndVal method was used to determine whether some species were characteristic of Arethusa habitat, and discriminant function analyses were performed to determine which factors were related to occupied and unoccupied sites. No characteristic species were identified when comparing paired plots. Occupied sites were mainly characterized by lower light availability at ground level (46%; mean), higher Floristic Quality Assessment Index (35), and smaller shrubs (55 cm) than unoccupied paired plots (61%, 32, and 61 cm respectively) from the same peatland. Water pH was the main factor discriminating occupied sites (5.5) from the unoccupied sites in peatlands where the species has never been present (3.9), pH being usually higher in plots with Arethusa. Ten species were characteristic of plots with Arethusa (including Larix laricina, Sphagnum palustre, and Aulacomnium warnstorfii) when compared to a priori suitable sites. Overall, our results suggest that Arethusa settles in poor to moderate Sphagnumdominated fen habitats rather than typical open bog habitats, as usually assumed.

Recent Vegetation Dynamics and Hydrological Changes in Bogs Located in an Agricultural Landscape

This study aims to reconstruct the recent dynamics of two bogs located in an agricultural landscape and to determine which factors favour tree expansion, the most salient change recently reported in treeless peatlands. The vegetation and hydrological dynamics of the bogs as well as land use changes in the vicinity were reconstructed using a combination of paleoecological, paleohydrological, and historical approaches. It was hypothesized that upland deforestation indirectly induced atmospheric mineral dust deposition on sites, thus increasing nutrient availability and triggering forest expansion. Results indicated that a widespread, but asynchronous tree expansion occurred in both bogs during the 20th century. However, no evidence suggesting that nutrient enrichment favoured the phenomenon was found. Forest expansion seems rather to have been favoured by drying of the peat surface, as a decrease of the water table depth coincided with the beginning of the forest encroachment on both sites. This drying correlated with the establishment of an in situ artificial drainage ditch on one site and with agricultural development in the catchment of the other. Local historical factors of each site apparently override regional factors such as climate anomalies or upland deforestation in explaining rapid, abrupt changes in bogs.