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Winter roads across subarctic peatlands are increasingly being used to access remote communities and resource development camps, yet relatively little is known on their ability to recover after abandonment. We evaluated the natural recovery of winter roads abandoned within 7 years on peatlands in the Hudson Bay Lowland, Canada. We sampled 5 winter roads of increasing age of abandonment and compared surface elevation, microtopography, active layer thickness, species cover, diversity, and composition between winter road clearances and adjacent undisturbed peatland. No differences in surface elevation and hummock-hollow microtopography were detected between road clearances and adjacent peatlands, but clearances had significantly thinner active layer, which persisted at least 7 years after abandonment. The cover of lichens, bryophytes, and vascular plants returned within 5 years to similar levels as in undisturbed peatlands, although species richness per quadrat remained lower and species composition differed. The limited recovery of black spruce on these peatlands and their slow growth indicates that the full recovery of vegetation structure on these road clearances will take decades. Future research should focus on the restoration of a Sphagnum carpet and on the interactions between a shallower active layer and the revegetation of abandoned winter roads.
The authors propose a model of glacial mass balance based on correlations with meteorological observations and data from climate re-analysis. The minimum input data required include the following: average monthly temperature on the glacier and in its vicinity during summertime for a reference time period, average monthly air temperature, and average precipitation total at the nearest weather station or from re-analysis. This model was used to hindcast the mass balance and its components at Werenskioldbreen (southern Svalbard) over the period 1912–2005. The hindcast specific mass balance was then used to estimate the change in the thickness of the snout of Werenskioldbreen over the period 1958–1990. These results were compared with results obtained using a cartographic method. Comparing the topographic maps, the glacier front lowered 28.7 m on average over 32 years. The average difference in the calculation of the change in glacier thickness between these two methods amounted to 3.7 m (based on meteorological data) and 0.2 m (using ERA-40). The discrepancy of less than 13% confirmed that the method is a reasonably accurate way of predicting past glacier mass balance. The proposed method can find a broad application in hindcasting the mass balances of small Svalbard glaciers where observation data are scarce or nonexistent.
Tree-limit ribbons, isolated ribbons of trees growing above, but close to the alpine tree limit, have been described previously only for North America. Here, we describe such ribbons from the Snowy Mountains, Australia. Spread of trees above the treeline on lee slopes is generally as ribbons perpendicular to the prevailing wind, with snowdrifts accumulating downwind suppressing seedling establishment. The ribbons exhibit long-term stability, with estimated stem ages of snowgum (Eucalyptus pauciflora subsp. niphophila) up to 500 years, and the lignotubers considerably older. Windblown branches containing viable seed may allow initial establishment of trees above treeline leading to the formation of ribbons. Seedling establishment uphill of the highest ribbons is rare because snowgum has no inherent seed dispersal mechanism, depending on gravity for dispersal. However, seedling establishment immediately downslope of the highest ribbons, normally suppressed by snowdrifts, is more common and appears to have occurred mainly post-1970. Whether seedlings that established under snowdrifts post-1970 will remain as krummholz or proceed to full tree status will depend on the future snow regime and the persistence of regular snowdrifts. However, there are trees that have established below ribbons but outside the influence of snowdrifts, that exist now as younger ribbons, in clumps, or as individuals, in areas that previously did not support trees.
Nitrification and denitrification are key microbiological processes in the soil nitrogen cycle and are the main biological sources of N2O emissions from soils. In this work, we measured gross nitrification and denitrification rates of northern Tibet alpine grassland ecosystems during the growing season and evaluated the influence of soil environmental factors. The results showed that the soil inorganic nitrogen concentration and gross nitrification and denitrification rates of both alpine meadow and alpine steppe varied obviously across the season. During the growing season mean values of gross nitrification and denitrification rates of the alpine meadow site were 3.0 and 2.3 times greater than those of the alpine steppe site, respectively. Both gross nitrification and denitrification rates were not significantly correlated with the determined soil characteristics which include soil microbial biomass, inorganic nitrogen, and soil temperature, except that gross nitrification seemed associated with the microsite where soil moisture was higher. Our results demonstrate that soil moisture can explain partly the higher soil nitrogen (N) transformation rates in alpine meadow sites, but soil N transformation microorganisms and enzyme activities studies covering prolonged observation periods are still needed to clarify the key soil environmental factors that control gross nitrification and denitrification processes in alpine grassland ecosystems.
Because the distribution of alpine tundra is associated with spatially limited cold climates, global warming may threaten its local extent or existence. This notion has been challenged, however, based on observations of the diversity of alpine tundra in small areas primarily due to topographic variation. The importance of diversity in temperature or moisture conditions caused by topographic variation is an open question, and we extend this to geomorphology more generally. The extent to which geomorphic variation per se, based on relatively easily assessed indicators, can account for the variation in alpine tundra community composition is analyzed versus the inclusion of broad indicators of regional climate variation. Visual assessments of topography are quantified and reduced using principal components analysis (PCA). Observations of species cover are reduced using detrended correspondence analysis (DCA). A “best subsets” regression approach using the Akaike Information Criterion for selection of variables is compared to a simple stepwise regression with DCA scores as the dependent variable and scores on significant PCA axes plus more direct measures of topography as independent variables. Models with geographic coordinates (representing regional climate gradients) excluded explain almost as much variation in community composition as models with them included, although they are important contributors to the latter. The geomorphic variables in the model are those associated with local moisture differences such as snowbeds. The potential local variability of alpine tundra can be a buffer against climate change, but change in precipitation may be as important as change in temperature.
For much of the 20th century, multiyear landfast sea ice (MLSI) formed a permanent ice cover in Yelverton Bay, Ellesmere Island. This MLSI formed following the removal of ice shelf ice from Yelverton Bay in the early 1900s, including the well-documented Ice Island T-3. The MLSI cover survived intact for 55–60 years until 2005, when >690 km2 (90%) of MLSI was lost from Yelverton Bay. Further losses occurred in 2008, and the last of the Yelverton Bay MLSI was lost in August 2010. Ground penetrating radar (GPR) transects and ice cores taken in June 2009 provide the first detailed assessment of MLSI in Yelverton Inlet, and indeed the last assessment now that it has all been replaced with first-year ice. A detailed history of ice shelf, glacier, and MLSI changes in Yelverton Bay since the early 1900s is presented using remotely sensed imagery (air photos, space-borne optical, and radar scenes) and ancillary evidence from in situ surveys. Recent changes in the floating ice cover here align with the broad-scale trend of long-term reductions in age and thickness of sea ice in the Arctic Ocean and Canadian Arctic Archipelago.
We characterized the effect of an extreme rain event on the biogeochemistry and ecosystem metabolism of an oligotrophic Sierra Nevada (California) lake. During a 10 hour period of an autumn season rainfall event, lake discharge increased from <1.0 L s-1 to over 3000 L s-1, reaching a rate one order of magnitude higher than found during peak snow-tmelt. Large quantities of terrestrial particulate and dissolved organic matter were washed into the lake. An entire season of autochthonous dissolved organic carbon (DOC) was flushed and replaced by allochthonous DOC as light attenuation increased by >300%. The resulting truncation of the photic zone, reduction of water column chlorophyll-a, and increase in particulate and dissolved organic matter available to microbes resulted in a 47% reduction in whole lake gross primary production and 30% increase in respiration relative to average autumn values. As a consequence, the lake went from being slightly autotrophic to strongly heterotrophic. If rain events increase in frequency, as many climate change models predict, increased terrestrial inputs to Sierran lakes may result in more frequent periods of reduced primary production, increased periods of hypoxia and anoxia, and an ecosystem shift toward net heterotrophy during the ice-free season.
Soil bacterial communities play a determining role in snow-covered ecosystems' response to global warming because of their role in nutrient recycling. However, little is known about how changes in snow-cover dynamics could affect bacterial community assembly in the short or long term. We examined the phylogenetic structure of soil bacterial communities sampled seasonally from early snowmelt (ESM) and late snowmelt locations (LSM) in temperate alpine tundra. Most of the variation in phylogenetic structure (i.e. β-diversity) was temporal rather than spatial and most observed deviations from random community assembly were towards phylogenetic clustering. Indeed, we observed phylogenetic clustering of Acidobacteria, Actinobacteria, and α-Proteobacteria during late winter in ESM locations, and a phylogenetic clustering of β-,γ-Proteobacteria, and Bacteroidetes during autumn in ESM and LSM locations probably linked to the onset of plant senescence and biomass decomposition. Interestingly, Acidobacteria were clustered in all LSM samples. Our study provides evidence of a high seasonal turnover of the phylogenetic structure of bacterial communities in alpine tundra soils, suggesting that climate-induced changes in snow cover can significantly alter the functioning of cold ecosystems through their filtering effects on soil bacteria communities.
The aim of this research was to determine how changes in soil moisture and temperature influence ecosystem C fluxes in the context of changing grazing regimes in subalpine grasslands in the Pyrenees. We (i) measured CO2 fluxes in the field in cattle- and sheep-grazed areas, and (ii) compared responses of CO2 and CH4 fluxes from soil turf samples from cattle- and sheep-grazed areas to changes in soil temperature and moisture. The cattle-grazed area showed greater ecosystem respiration and gross ecosystem photosynthesis than the sheep-grazed areas. With respect to the temperature and moisture treatments, the two areas responded in a similar way: Soil moisture was the strongest driver of soil respiration rates; although temperature also increased CO2 effluxes from the soils, the effects were transient. The greatest effluxes of CO2 were found in soils incubated at elevated temperature and 80% soil moisture content. Methane fluxes were only influenced by the moisture treatment, with the greatest methane oxidation rates found at 40% soil moisture content. We conclude that regional changes in moisture availability resulting from climate change are likely to be the most important driver of soil respiration and methane fluxes in these grazed subalpine ecosystems.
The paradigm that winter is a dormant period of soil biogeochemical activity in high elevation or high latitude ecosystems has been amply refuted by recent research. Carbon dioxide (CO2) released from cold or snow-covered soil is a substantial component of total annual ecosystem carbon fluxes. Recent investigations have shown that the late-winter/early-spring transition is a period of high biogeochemical activity. However, little is known about the temporal dynamics of CO2 from the snowpack itself during periods of snowmelt. We present a case study of three snowmelt events at a high-elevation site in northern Arizona during which we measured changes in CO2 concentrations and fluxes above the snow and within the soil profile, and characterized the soil physical environment and site meteorological variables. We show that large pulses of CO2 were emitted to the atmosphere during snowmelt, and we present evidence that these pulses came from CO2 stored in snowpack. Earlier and more frequent snowmelts worldwide caused by climate change have the potential to alter the timing of release of CO2 from land to atmosphere.