Monique Poulin

Conservation of bog plant species assemblages: Assessing the role of natural remnants in mined sites

Bogs, economically valuable wetlands, are subjected to exploitation in southern Canada. We addressed plant conser- vation within bogs mined for peat, in which small undisturbed remnants are left, mostly at the margins of the mined areas. The main goal of the study was to test whether these remnants act as refuges for plants which could recolonize areas that are planned for restoration after mining is completed. Mosses, lichens and vascular plants were sampled in rem- nants of 24 mined bogs in southeastern Canada during the summer of 1997. The vegetation was also sampled at the margins and centres of 24 nearby natural bogs in plots similar in size to these remnants. Using similarity analysis and ordination techniques, we found that plant species assemblages in rem- nants of mined bogs differ from those near the margins of natural bogs, and that certain species are associated with the centre of natural bogs, due to the presence of pools. We also showed that water conditions of remnants are affected by drain- age due to peat mining. Sphagnum moss showed itself to be a key indicator of mining effects on vegetation. Implications for peat resource management and bog conservation are discussed.

Restoration of riparian vegetation : a global review of implementation and evaluation approaches in the international, peer-reviewed literature

We examined how restoration of riparian vegetation has been implemented and evaluated in the scientific literature during the past 25 years. A total of 169 papers were read systematically to extract information about the following: 1) restoration strategies applied, 2) scale of monitoring and use of reference sites, 3) metrics used for evaluation, and 4) drivers of success. Hydro-geomorphic approaches (e.g., dam operations, controlled floods, landform reconfiguration) were the most frequent, followed by active plant introduction, exotic species control, natural floodplain conversion and grazing and herbivory control. Our review revealed noteworthy limitations in the spatio-temporal approaches chosen for evaluation. Evaluations were mostly from one single project and frequently ignored the multi-dimensional nature of rivers: landscape spatial patterns were rarely assessed, and most projects were assessed locally (i.e., ≤meander scale). Monitoring rarely lasted for more than six years and the projects evaluated were usually not more than six years old. The impact of the restoration was most often (43%) assessed by tracking change over time rather than by comparing restored sites to unrestored and reference sites (12%), and few projects (30%) did both. Among the ways which restoration success was evaluated, vegetation structure (e.g., abundance, density, etc.) was assessed more often (152 papers) than vegetation processes (e.g., biomass accumulation, survival, etc.) (112 papers) and vegetation diversity (78 papers). Success was attributed to hydro-geomorphic factors in 63% of the projects. Future evaluations would benefit from incorporating emerging concepts in ecology such as functional traits to assess recovery of functionality, more rigorous experimental designs, enhanced comparisons among projects, longer term monitoring and reporting failure.

Spontaneous revegetation of cutwaway peatlands of North America

Modern extraction methods permit peat to be extracted to the minerotrophic layer of ombrotrophic peatlands (bogs). As the environmental conditions of these harvested peatlands are similar to minerotrophic peatlands (fens), such sites should be restored towards a fen system. However, it is not known whether fen species would recolonize such harvested sites on their own. We surveyed vegetation and environmental variables in 28 harvested peatlands with minerotrophic residual peat across Canada and in Minnesota, USA, and compared them to 11 undisturbed fens. Compared to harvested bogs previously studied, the harvested fens sampled in this study revegetated remarkably quickly (50%–70% vegetation cover) when the hydrological conditions were suitable. However, revegetation was less extensive for sites that were still drained (25% vegetation cover). A high water table and a thin layer of residual peat were the most important factors contributing to rapid recolonization rates. Although the harvested fens were rapidly recolonized, species composition was not the same as observed on undisturbed fens. Carex and Sphagnum, dominant in undisturbed fens, generally did not recolonize harvested fens. Thus, whether the goal is to increase species richness or to ensure the return of peat accumulating functions, fen species may have to be actively introduced.

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.

Site complementarity between biodiversity and ecosystem services in conservation planning of sparsely-populated regions.

The consequences of considering ecosystem services (ES) in conservation assessment are still widely debated. The degree of success depends on the extent to which biodiversity and ES can be secured under joint conservation actions. Unlike biodiversity, ES conservation is inseparably linked to human beneficiaries. Reconciling biodiversity with ES and conservation can be particularly challenging in sparsely populated areas. This study, in a sparsely-populated region of eastern Canada, focused on freshwater wetland biodiversity and ten ES provided by wetlands. Within a given maximal total area, the results showed that planning for biodiversity underrepresented local flow ES supply by 57% and demand by 61% in conservation networks. Planning for ES alone underrepresented wetland biodiversity surrogates by an average of 34%. Considering both biodiversity and ES simultaneously, all of the biodiversity and ES targets were achieved with only a 6% mean increase in area. Achieving all conservation targets starting from a network that was primarily built for either ES or biodiversity features alone was two to five times less efficient than considering both ES and biodiversity simultaneously in conservation assessment. A better framework is required to translate these spatial synergies into effective joint conservation actions.

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.

Spatial processes structuring riparian plant communities in agroecosystems: implications for restoration

The disruption of hydrological connectivity by human activities such as flood regulation or land-use changes strongly impacts riparian plant communities. However, landscape-scale processes have generally been neglected in riparian restoration projects as opposed to local conditions, even though such processes might largely influence community recovery. We surveyed plant composition of field edges and riverbanks in 51 riparian zones restored by tree planting (565 1-m2 plots) within two agricultural watersheds in southeastern Québec, Canada. Once the effects of environmental variables (hydrology, soil, agriculture, landscape, restoration) were partialled out, three models of spatial autocorrelation based on Morans eigenvector maps and asymmetric eigenvector maps were compared to quantify the pathways and direction of the spatial processes structuring riparian communities. The ecological mechanisms underlying predominant spatial processes were then assessed by regression trees linking species response to spatial gradients to seed and morphological traits. The structure of riparian communities was predominantly related to unidirectional spatial gradients from upstream to downstream along watercourses, which contributed more to species composition than bidirectional gradients along watercourses or overland. Plant traits selected by regression trees explained 22% of species response to unidirectional upstream-downstream gradients in field edges and 24% in riverbanks, and predominantly corresponded to seed traits rather than morphological traits of the adult plants. Our study showed that even in agriculturally open landscapes, water flow remains a major force structuring spatially riparian plant communities by filtering species according to their seed traits, thereby suggesting long-distance dispersal as a predominant process. Preserving hydrological connectivity at the watershed-scale and restoring riparian plant communities from upstream to downstream should be encouraged to improve the ecological integrity of rivers running through agricultural landscapes.

Sensitivity of spectral indices to CO2 fluxes for several plant communities in a Sphagnum-dominated peatland

Peatlands may play an important role in global carbon cycles, and thus developing better estimates of carbon exchange in those ecosystems has become a main concern. In this study, the relationship between spectral indices and CO2 fluxes was tested for different communities in a Sphagnum-dominated peatland. Fluxes were measured with a portable climate-controlled chamber while reflectance was simultaneously recorded using a hand-held spectroradiometer. A laboratory experiment was also conducted to select the water-related index most correlated with Sphagnum water content to regulate the normalized difference vegetation index (NDVI) values obtained in the field. The laboratory experiment showed a strong correlation between Sphagnum water content and all spectral indices, namely the water index (WI), normalized difference water index (NDWI), and relative depth index (RDI) (r = 0.753–0.993). WI was the index selected for regulating NDVI values. Indices tested in the field for CO2 flux estimations were (i) NDVI, (ii) NDVI/WI, (iii) NDVI × sPRI (photochemical reflectance index), and (iv) the chlorophyll indices CI and CIm. NDVI alone was a poor predictor of net ecosystem exchange (NEE, r2 = 0.12) and gross photosynthesis (PG, r2 = 0.15), and NDVI × sPRI and NDVI/WI showed moderate adjustments to CO2 fluxes (NEE, r2 = 0.26 and 0.30; PG, r2 = 0.38 and 0.43, respectively, for each index). The relationship between CO2 fluxes and chlorophyll indices was reasonably well adjusted (CI and NEE, r2 = 0.37; CI and PG, r2 = 0.55; CIm and NEE, r2 = 0.38; CIm and PG, r2 = 0.57), and these indices may be the most promising for mapping the spatial distribution of CO2 fluxes in the future.

Population isolation shapes plant genetics, phenotype and germination in naturally patchy ecosystems

Aims Habitat connectivity is important in conservation since isolation can diminish the potential of a population for adaptation and increase its risk of extinction. However, conservation of naturally patchy ecosystems such as peatlands has mainly focused on preserving specific sites with exceptional characteristics, neglecting the potential interconnectivity between patches. In order to better understand plant dynamics within a peatland network, we assessed the effect of population isolation on genetic distinctiveness, phenotypic variations and germination rates using the peatland-obligate whitefringed orchid (Platanthera blephariglottis). Methods Fifteen phenotypic traits were measured for 24 individuals per population (20 distinct populations, Quebec, Canada) and germination rates of nearly 20 000 seeds were assessed. Genetic distinctiveness was quantified for 26 populations using single nucleotide polymorphism markers obtained via a pooled genotyping-by-sequencing approach. Geographic isolation was measured as the distance to the nearest population and as the number of populations occurring in concentric buffer zones (within a radius of 2, 5 and 10 km) around the studied populations. Important Findings All phenotypic traits showed significant differences among populations. Genetic results also indicated a pattern of isolation-bydistance, which suggests that seed and/or pollen exchange is restricted geographically. Finally, all phenotypic traits, as well as a reduced germination rate, were correlated with either geographic isolation or genetic distance. We conclude that geographic isolation likely restricts gene flow, which in turn may affect germination. Consequently, it is imperative that conservation programs take into account the patchy nature of such ecosystems, rather than targeting a few specific sites with exceptional character for preservation.