Tolerance to Sand Burial, Trampling, and Drought of Two Subarctic Coastal Plant Species (Leymus mollis and Trisetum spicatum)

In order to ensure the sustainable development of the North, increased anthropogenic pressure on subarctic environments must be accompanied by appropriate restoration techniques. Locally adapted restoration guidelines need to rely on sound ecological knowledge of the species used in restoration trials. We evaluate the tolerance (emergence and biomass production) of two coastal species (Leymus mollis and Trisetum spicatum) to sand burial, trampling, and drought, all major constraints to plant colonization in the village of Whapmagoostui-Kuujjuarapik in subarctic Quebec. In three 11-week greenhouse experiments, plants were submitted to three intensities of sand burial (0.0, 0.5, and 1.0 cm per week), trampling events (none, once per week, once per day) and drought (50 mL of water every other day, every week, and every other week). While T. spicatum performance decreased under both moderate and high sand burial intensities, L. mollis tolerated moderate burial intensity. Both species were able to sustain trampling, although the performance of T. spicatum was reduced under high trampling intensity. Finally, neither species could tolerate moderate and high drought intensities, suggesting that watering needs to be included in any restoration initiatives. Since L. mollis performed better than T. spicatum in the sand burial experiment, we recommend the use of this species in future small-scale restoration trials.Dans le but d’assurer le développement durable du Nord, des méthodes de restauration appropriées doivent être développées en réponse aux perturbations de nature anthropique accrues. De telles techniques de restauration régionales doivent cependant reposer sur de solides connaissances de l’écologie des espèces utilisées. Dans cette étude, nous avons évalué la tolérance (émergence et production de la biomasse) de deux espèces côtières (Leymus mollis et Trisetum spicatum) à l’ensablement, au piétinement et à la sécheresse, trois contraintes majeures inhibant la recolonisation végétale dans le village subarctique de Whapmagoostui-Kuujjuarapik, au Québec. Pour ce faire, trois expériences en serre d’une durée de 11 semaines ont été menées dans lesquelles les individus des deux espèces ont été soumis respectivement à trois intensités d’ensablement (0,0, 0,5 et 1,0 cm par semaine), de piétinement (aucun, une fois par semaine, une fois par jour) et de sécheresse (50 mL d’eau à tous les 2, 7 et 14 jours). Alors que la performance de T. spicatum a diminué lorsque soumis aux régimes d’ensablement intermédiaire et élevé, L. mollis a toléré le régime d’ensablement intermédiaire. Dans l’expérience de piétinement, les deux espèces considérées ont relativement bien supporté le piétinement imposé, si ce n’est d’une légère diminution de la performance de T. spicatum lorsque soumis à un fort piétinement. Finalement, ni l’une ni l’autre des espèces ne pouvait tolérer les deux intensités de sécheresse (intermédiaire et élevé), ce qui laisse entendre que les plantes doivent être arrosées dans le cadre d’initiatives de restauration. Puisque L. mollis a donné de meilleurs résultats que T. spicatum en matière d’ensablement, nous privilégions l’utilisation de L. mollis pour les futures initiatives de restauration à petite échelle

Chemical composition of the unexplored volatile fraction of betula glandulosa, a prevalent shrub in Nunavik, Québec

The volatile fraction of the leaves of Betula glandulosa Michx. has been investigated for its secondary metabolite composition by GC/MS and GC/FID. The rapid expansion of this shrub species in subarctic landscapes, like the ones found in Nunavik (Northern Québec, Canada), highly impacts ecosystem dynamics. Yet, despite its abundance, few phytochemical investigations have yet been conducted on this species. In this study, we present the first phytochemical investigation of the volatile metabolites of B. glandulosa leaves. Although no essential oil was isolated, volatile compounds were extracted from the hydrosol by steam distillation. The main metabolites observed were linalool (14.6–19.0 %), C6 oxylipins (known as green leaf volatiles, GLV; total of 18.2–40.2 %), eugenol (1.6–8.6 %) and α-terpineol (3.3–4.8 %). Dwarf birch is an important food source for insects and herbivores, so knowledge of its metabolite composition could help understand parts of its functional role in subarctic ecosystems. The composition of the volatile fraction could serve as marker for differentiating B. glandulosa from other dwarf birch species like Betula nana L

Influence of climatic conditions on growth rings of Salix uva-ursi Pursh from the southeastern shore of Hudson Bay, Subarctic Canada

Over the past decades, warmer air temperature and spatiotemporal changes in the amount andpatterns of precipitation have been observed at high latitudes. Such interannual variability inclimatic conditions has a strong influence on the dynamics of biological processes regulatingterrestrial ecosystems. Dendroclimatology can improve our understanding of the impacts ofclimate change on vegetation. Based on ring width and frost rings of bearberry willow (Salix uva-ursi) individuals sampled on the southeastern shore of Hudson Bay, Nunavik (Subarctic Québec,Canada), we built a reliable 105-year growth chronology. A complex dendroclimatological analy-sis, using the standard approach (mean temperature and precipitation sums), extreme variables,and various climatological indices based on daily data, was conducted in order to preciselydescribe the relationship between annual variations in growth rings and climatic conditions.The growth of Low Arctic willows in the Hudson Bay region is determined by changes in airtemperatures as well as precipitation during the summer. However, temperature increases andreductions in amounts of rainfall may intensify drought stress, which is unfavorable for thisspecies. We found that analysis of daily amounts and intensity of precipitation improved ourunderstanding of the factors conditioning the growth of the studied species in an extremehabitat

Assisted Revegetation in a Subarctic Environment: Effects of Fertilization on the Performance of Three Indigenous Plant Species

Published VersionAssisted re-vegetation is particularly difficult in subarctic and arctic ecosystems where the impact of anthropogenic activities can be extensive and natural plant regeneration is slow. The construction of a military base in the 1950s at Kuujjuarapik–Whapmagoostui in northern Quebec destroyed most of the vegetation cover. Afterwards, other anthropogenic disturbances linked to the village expansion (housing, ATV traffic, pedestrian trampling) have slowed down the recovery process. To provide residents with low-cost but efficient assisted revegetation techniques, we evaluated the performance (seedling emergence, survival, and biomass production) of three indigenous plant species (Leymus mollis, Lathyrus japonicus, Trisetum spicatum) submitted to different levels of mineral and organic fertilizer additions in both a greenhouse experiment and a field plantation in the village. In the greenhouse experiment, moderate mineral fertilization had positive impacts on seedling emergence and both above ground and below ground biomass of L. mollis. The magnitude of this impact on biomass was greater when mineral fertilization was combined with organic fertilization. The effects of mineral fertilization were negative on the other two species, especially at higher fertilization levels. However, after two growing seasons, a moderate level of mineral fertilizer in the field plantation had positive effects on the cover and above ground biomass of all three species. Overall, organic fertilization from the substrate of a nearby marsh did not enhance plant performance in either experiment. Planting seeds of L. mollis or T. spicatum in combination with a moderate level of mineral fertilization at the time of planting provides a low-cost assisted re-vegetation treatment for subarctic villages

Is subarctic forest advance able to keep pace with climate change?

Published VersionRecent climate warming and scenarios for further warming have led to expectations of rapid movement of ecological boundaries. Here we focus on the circumarctic forest–tundra ecotone (FTE), which represents an important bioclimatic zone with feedbacks from forest advance and corresponding tundra disappearance (up to 50% loss predicted this century) driving widespread ecological and climatic changes. We address FTE advance and climate history relations over the 20th century, using FTE response data from 151 sites across the circumarctic area and site-specific climate data. Specifically, we investigate spatial uniformity of FTE advance, statistical asso ciations with 20th century climate trends, and whether advance rates match climate change velocities (CCVs). Study sites diverged into four regions (Eastern Canada; Central and Western Canada and Alaska; Siberia; and Western Eurasia) based on their climate history, although all were characterized by similar qualitative patterns of behaviour (with about half of the sites showing advancing behaviour). The main associations between climate trend variables and behaviour indicate the importance of precipitation rather than temperature for both qualitative and quantitative behav iours, and the importance of non-growing season as well as growing season months. Poleward latitudinal advance rates differed significantly among regions, being small est in Eastern Canada (~10 m/year) and largest in Western Eurasia (~100 m/year). These rates were 1–2 orders of magnitude smaller than expected if vegetation dis tribution remained in equilibrium with climate. The many biotic and abiotic factors influencing FTE behaviour make poleward advance rates matching predicted 21st century CCVs (~103–104 m/year) unlikely. The lack of empirical evidence for swift forest relocation and the discrepancy between CCV and FTE response contradict equilibrium model-based assumptions and warrant caution when assessing global change-related biotic and abiotic implications, including land–atmosphere feedbacks and carbon sequestration

Divergence of Arctic shrub growth associated with sea ice decline

Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences. However, determining sea ice effects on tundra vegetation remains a challenge. In this study, we examined the universality or lack thereof in tundra shrub growth responses to changes in SIE and summer climate across the Pan-Arctic, taking advantage of 23 tundra shrub-ring chronologies from 19 widely distributed sites (56°N to 83°N). We show a clear divergence in shrub growth responses to SIE that began in the mid-1990s, with 39% of the chronologies showing declines and 57% showing increases in radial growth (decreasers and increasers, respectively). Structural equation models revealed that declining SIE was associated with rising air temperature and precipitation for increasers and with increasingly dry conditions for decreasers. Decreasers tended to be from areas of the Arctic with lower summer precipitation and their growth decline was related to decreases in the standardized precipitation evapotranspiration index. Our findings suggest that moisture limitation, associated with declining SIE, might inhibit the positive effects of warming on shrub growth over a considerable part of the terrestrial Arctic, thereby complicating predictions of vegetation change and future tundra productivity

Reproduction as a bottleneck to treeline advance across the circumarctic forest tundra ecotone

Published versionThe fundamental niche of many species is shifting with climate change, especially in sub-arctic ecosystems with pronounced recent warming. Ongoing warming in sub-arctic regions should lessen environmental constraints on tree growth and reproduction, leading to increased success of trees colonizing tundra. Nevertheless, variable responses of treeline ecotones have been documented in association with warming temperatures. One explanation for time lags between increasingly favourable environmental conditions and treeline ecotone movement is reproductive limitations caused by low seed availability. Our objective was to assess the reproductive constraints of the dominant tree species at the treeline ecotone in the circumpolar north. We sampled reproductive structures of trees (cones and catkins) and stand attributes across circumarctic treeline ecotones. We used generalized linear mixed models to estimate the sensitivity of seed production and the availability of viable seed to regional climate, stand structure, and species-specific characteristics. Both seed production and viability of available seed were strongly driven by specific, sequential seasonal climatic conditions, but in different ways. Seed production was greatest when growing seasons with more growing degree days coincided with years with high precipitation. Two consecutive years with more growing degree days and low precipitation resulted in low seed production. Seasonal climate effects on the viability of available seed depended on the physical characteristics of the reproductive structures. Large-coned and -seeded species take more time to develop mature embryos and were therefore more sensitive to increases in growing degree days in the year of flowering and embryo development. Our findings suggest that both moisture stress and abbreviated growing seasons can have a notable negative influence on the production and viability of available seed at treeline. Our synthesis revealed that constraints on pre-dispersal reproduction within the treeline ecotone might create a considerable time lag for range expansion of tree populations into tundra ecosystems

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements