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Many tundra plant species rely more heavily on clonal propagation than on sexual reproduction. However, if reproduction bottlenecks are alleviated, shifts in the balance between these strategies can occur. To better understand the colonization and expansion dynamics of clonal dwarf shrubs in a rapidly changing environment, we monitored a crowberry population (Empetrum hermaphroditum) on a sand dune system in subarctic Québec. Our objectives were to quantify survival, recruitment, and growth and to determine whether performance varied across a topographic and successional gradient. In 2012, we resurveyed a 6-ha plot where all individuals had been counted in 2007. Along the successional gradient, we measured vegetation cover, soil characteristics, shoot elongation, and seed germination. Over the 2007–2012 period, the population continued to experience abundant recruitment, fast growth, and low mortality, resulting in a 40% increase in population size and a 244 m2 increase in cover. Performance patterns did not match the dune successional gradient; instead, individuals at intermediate positions showed better growth and produced more viable seeds. The ability of crowberry to successfully establish from seed might have been enhanced by the regional warming observed since the 1990s and seems to be part of a dual strategy allowing crowberry to fill gaps while continuing to spread efficiently on the dune system via clonal growth.
This paper employs remote sensing methods to address a large number of glaciers and their change in the Chinese Tien Shan Mountains for the period from 1959/1972 to 2010/2012. Our results show that the total area of the 1428 glaciers studied decreased from 1299 ± 4 km2 in 1959/1972 to 1013 ± 4 km2 in 2010/2012. This 22% reduction in glacier surface area represents a total loss of 287 km2. The rate of glacier shrinkage throughout the nine regions varied from 0.3% a-1 to 0.8% a-1, and approximate individual glacier area loss varied from 0.002 km2 a-1 to 0.008 km2 a-1.The greatest decrease in glacier extent occurred in the Ili River valley, followed by the Toutun River valley and Urumqi River valley. In contrast, relatively minor decreases occurred in the Miaoergou Gully and Aksu River valley regions.
In alpine tundra the influence of snow-cover duration (SCD) and pedoclimatic conditions on soil nutrient forms during the growing season has received little attention. The hypothesis that SCD influences the soil temperature, which in turn can affect the annual changes in topsoil nitrogen (N) and carbon (C) forms, was tested for five growing seasons at three study sites in the alpine tundra of the NW Italian Alps. Among the pedoclimatic conditions studied (soil temperature, soil moisture, and number of freeze/thaw cycles), the mean soil temperature of the growing season was inversely correlated with the SCD (p < 0.01), which ranged from 216 to 272 days. Independently from the soil characteristics (e.g., degree of evolution), the microbial carbon (Cmicr) of the growing season was inversely correlated with the SCD and the mean soil temperature of the snow-covered season, suggesting the consumption of soil resources made by the Cmicr under the snowpack. During the growing season ammonium (N-NH4), dissolved organic carbon (DOC), and Cmicr were positively correlated with soil temperature and moisture. Path analysis shows that the interannual variability of topsoil N and C forms was significantly controlled by the pedoclimatic conditions recorded in both the snow-covered and the subsequent growing seasons, which in turn were influenced by SCD. Therefore, SCD played a fundamental role in terms of pedoclimatic conditions during the growing season, contributing to explaining the interannual variability of soil N and C forms, and may be a key factor for predicting the nutrient cycling in alpine tundra in the context of a changing climate.
A species' use of space provides insight into fundamental resource requirements and population dynamics. Here we investigate how microhabitat features and intraspecific interaction contribute to space use by the singing vole (Microtus miurus) on arctic tundra. We used mark-recapture of singing voles to estimate home range using a kernel density estimator. To assess intraspecific interactions, regions within home ranges were classified as “exclusive” or “shared” based on overlap among individuals. The spatial distribution of singing vole encounters was analyzed in conjunction with multivariate hierarchical cluster analysis of vegetation cover to assess microhabitat affinity. “Shared” regions within home ranges were used more than expected based on proportional availability. We observed significant affinities for microhabitats at both the scale of individual home ranges and of the singing vole population. Our results suggest that heterogeneity in microhabitat features and social interactions are important factors in structuring singing vole space use. These results have implications for the impact of singing vole activity on tundra plant communities and for the resilience of the singing vole and other arctic microtine rodents to stochastic climatic conditions.
Subarctic ecosystems are experiencing rapid changes as a result of climate warming and more frequent and severe disturbances. There is considerable uncertainty regarding ecological trajectories following disturbance in forested ecosystems underlain by permafrost because their structure and function is controlled by feedbacks among soil conditions, vegetation, and ground thermal regime. In this paper, we studied post-disturbance ecosystem recovery in an area of discontinuous permafrost 32 years after construction and abandonment of a winter access road in Nahanni National Park Reserve (NNPR). Ecosystem recovery was examined by comparing disturbed (road) and undisturbed (adjacent to the road) sites in the following terrain types: spruce peatland, black spruce parkland, deciduous forest, and alpine treeline terrain. Our field data show that disturbances to discontinuous permafrost terrain can lead to large and persistent changes to ecosystem composition and structure. Our findings indicate that the ecological response of discontinuous permafrost to disturbance and climate warming will depend on interactions between soil conditions and vegetation communities. In instances where disturbance to discontinuous permafrost fundamentally disrupts stabilizing interactions between soil conditions and vegetation communities, we should expect lasting changes to ecosystem structure and function.
When the capacity for photosynthesis is constrained by unfavorable growing conditions, excess absorbed light is safely lost from leaves via thermal energy dissipation—a photoprotective mechanism ubiquitous among higher plants. The relatively low irradiance conditions yet stressful growing environment of the arctic tundra suggest contrasting hypotheses regarding the necessity for plant investment in photoprotection. To examine these hypotheses, the photoprotective pigments of the xanthophyll cycle were investigated in conjunction with non-photochemical quenching (NPQ) of chlorophyll fluorescence emission in two dominant arctic shrub species, Salix pulchra and Betula nana. The xanthophyll cycle pool sizes of S. pulchra leaves were substantially higher than those reported in most other higher plant species, whereas B. nana leaves maintain modestly high xanthophyll cycle pool sizes. In addition, high retention of de-epoxidized xanthophyll cycle pigments in both species and saturation of xanthophyll cycle conversion at low-light intensities were observed and associated with high levels of NPQ. The xanthophyll cycle leaf pigment pools reported are among the first published for arctic plants and support the hypothesis that foliar xanthophyll cycle activity is greater in environments prone to harsher growing conditions.
Climate-driven shrub expansion is altering the distribution of animal communities in the Arctic. A better understanding of habitat requirements is needed to accurately predict the response of herbivore communities to shrub expansion. We examined patterns of browsing by moose (Alces alces), snowshoe hare (Lepus americanus), and ptarmigan (Lagopus lagopus, L. muta) across the tundra of northern Alaska to determine whether forage requirements explain the distribution of herbivores in this ecosystem. In addition, we examined the potential for competition among these three shrub-dependent species. We recorded shrub characteristics and browsing levels at 59 sites along a 568 km riparian transect spanning from the Brooks Range to the Arctic Coast. Mean shrub height was positively correlated with browsing intensity for all three species (r = 0.40–0.71). The minimum shrub height threshold for hare occurrence (≥87 cm, 95% CI: 67–94) was similar to that for moose (≥81 cm, 95% CI: 65–96), whereas ptarmigan were nearly ubiquitous (≥3 cm, lower 95% CI = 0). Diet overlap among herbivores was nearly complete, with all three species heavily browsing feltleaf willow (Salix alaxensis). Our findings indicate that unlike moose and ptarmigan, forage availability does not appear to control the distribution of snowshoe hares in the Arctic. Resource competition may further affect distribution patterns within this guild as shrub cover continues to expand.
Soil moisture (SM), snow depth (SND), and air temperature are crucial factors for the soil thermal and hydraulic regimes in the permafrost regions. This paper analyzes the contribution of these factors to active layer thickness (ALT) under different climate change scenarios in northern hemisphere permafrost regions, using simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) for the early (2016–2035, EP), middle (2046–2065, MP), and late (2080–2099, LP) periods of the 21st century. The results indicate that, with the temperature increasing, the relation between ALT and SM, SND, and mean annual air temperature (MAAT) will change in different permafrost regions. During 1986–2005 (reference period), ALT correlates significantly with SND in Europe only, the contribution of MAAT and SM to ALT are significant over the Tibetan Plateau (TP) and in North America (NA). MAAT is the only significant contribution factor to ALT deepening for all regions. In the 21st century, for the high Representative Concentration Pathways (RCP8.5), MAAT plays a dominant role in ALT over the TP and NA; however, snow effect is enhanced under RCP2.6 and RCP4.5 in Europe and NA. With temperature increasing, the importance of SM and SND alternates for low and middle emission, and gradually declines for high emission. In general, MAAT is the main contributor to ALT during the 21st century, while the impact of SM and SND declines with increasing temperature. Contribution of SM, SND, and MAAT to ALT varies, which illustrates the differences in regional thermal and hydraulic regimes from warming in permafrost regions.
Instrumental records indicate a warming of approximately 0.8 °C has occurred in the Mount Everest region since the 1980s, which has resulted in a 100–300 m rise in the height at which the ground is permanently frozen as well as a retreat and thinning of Everest's glaciers. For some time, there have been concerns that this warming and the resultant changes in the region's glaciers may be increasing the risks for travellers to Mount Everest as well as the indigenous populations who support them. On 18 April 2014, an avalanche caused by the collapse of a large serac swept down Mount Everest's Khumbu Ice Fall resulting in the deaths of 16 Sherpa. Although satellite imagery has been used to estimate the size of the serac, in situ data on the avalanche itself has not been available. Here we show that this event coincided with an approximate 15-min-long wind, thermal, and moisture anomaly, which was observed at the Nepal Climate Observatory-Pyramid situated 10 km from Mount Everest. We argue that this anomaly was associated with the avalanche and thereby provides some information on its scale and duration as well as a potential mechanism to monitor future events in this remote and data-sparse region.