We report on a limnological study of ice-covered Upper Dumbell Lake (Ellesmere Island, Canada) conducted during the summer of 1959. The lake was vertically profiled for physical (temperature, light), chemical (alkalinity, pH, oxygen, nutrients), and biological (chlorophyll a, gross and net primary productivity) variables on 21 dates spanning from early July to early September. Zooplankton density and age structure were also determined on four dates. Factors such as temperature, alkalinity, pH, and oxygen varied little with depth or over time, whereas nutrients (nitrate, dissolved silica, soluble reactive phosphorus), light, chlorophyll a, and gross and net photosynthesis varied substantially. Comparing July to August, nitrate and light intensity decreased while dissolved silica, chlorophyll a, and gross and net primary production increased, with two distinct peaks in algal biomass occurring over the month of August. Chlorophyll a in this lake was negatively correlated with nitrate concentrations, suggesting uptake of nitrogen as algal biomass increased. The copepod Limnocalanus macrurus was the dominant zooplankton taxon present; the age structure of the population advanced over the summer. This study reveals the dynamic nature of vertical habitat gradients even under the ice of Arctic lakes and provides important baseline data for conditions in an Arctic lake during the mid-20th century.

Plant community properties such as species richness, evenness, and composition vary along environmental gradients. Arid and semi-arid ecosystems, such as the central Tibetan Plateau, are thought to be sensitive to changes in temperature and water availability, and also influenced by a long history of herbivore grazing. We used linear mixed effect models and Canonical Correspondence Analysis to explore how plant community properties varied along gradients of elevation, soil moisture, grazing intensity, solar radiation, ground surface roughness (ground concavity), and pika abundance in an alpine meadow ecosystem in central Tibet. We found that species richness increased with elevation. Species evenness increased with soil moisture at lower elevation, but decreased with soil moisture at higher elevation. Species composition was significantly associated with all environmental variables except solar radiation. The abundance of the dominant plant species, K. pygmaea, which is driven primarily by soil moisture, was also an important variable. We conclude that open patches (habitat), associated with elevation, number of pika burrows and surface roughness, and soil moisture and its effects on K. pygmaea were the most important environmental variables creating variation in plant community properties across this landscape.

Climate-based models predict global warming will cause mountain plants to migrate upward with local extirpation of species currently restricted to the highest elevations. Alpine monitoring studies have generally documented changes in alpine plant distributions consistent with these predictions; however, relatively few such studies have been reported from North America. I estimated canopy cover in 71 permanent microplots at two alpine moist-turf sites in Glacier National Park, Montana, U.S.A., three times between 1988 and 2011. Mean annual and summer temperatures were approximately 0.6 and 0.7 °C higher than the previous four decades, respectively. Plants more restricted to high elevations declined more than species with a broader elevational amplitude during this time. Dicots were more likely to have declined than monocots. These data support predictions and provide information that may help refine climate-envelope models.

Grazing by livestock can have positive, neutral, and/or negative effects on vegetation depending on the intensity and type of grazing. This includes grazing by pack animals used for tourism in mountain protected areas. We assessed the response of vegetation to the exclusion of grazing by pack animals over one growing season in the highest park in the Southern Hemisphere, Aconcagua Provincial Park, dry Central Andes. Twenty pairs of exclosures and unfenced quadrats were established in three high-altitude Andean alpine meadows that are intensively grazed by horses and mules used by commercial operators to transport equipment for tourists. Vegetation parameters, including height, cover, and composition were measured in late spring when exclosures were established and ~120 days later at the end of the growing season along with above-ground biomass. Data was analyzed using mixed models and ordinations. Vegetation responded rapidly to the removal of grazing. Vegetation in exclosures was more than twice as tall, had 30% more above-ground biomass, a greater cover of grasses including the dominant Deyeuxia eminens, and less litter than grazed quadrats. These changes in the vegetation from short-term exclusion of grazing are likely to increase the habitat quality of the meadows for native wildlife.

Hydrology, permafrost, and vegetation will likely respond to warming of northern latitudes with concurrent shifts in channel form and network pattern. At present, data on channel structure and networks in most northern regions are sparse, thus restricting any comprehensive understanding of channel processes or predictions of change in response to warming. We conducted a survey in 2011 of stream hydraulic geometry and network pattern in an upland headwater catchment of the Yukon River basin that is underlain by discontinuous permafrost. We found atypical hydraulic geometry exponents for depth and velocity but not for width and slope. We also found the study catchment to have unusually low drainage density and bifurcation ratios. Our data support the hypothesis that snow and channel ice decrease geomorphic effectiveness during snowmelt, which ultimately constrains channel and network development. Additionally, qualitative data support the hypothesis that dense riparian vegetation promotes bank stabilization and leads to nearly vertical channel walls in small streams, thus leading to anomalous hydraulic geometry. Simple metrics such as the drainage density and hydraulic geometry relationships may prove to be useful metrics of boreal and subarctic warming and permafrost thaw, and this study may serve as an important baseline to evaluate future changes.

Alpine and subalpine meadows are often hotspots of water availability and biodiversity in montane landscapes, but we know little about whether these attributes also make meadows hotspots of greenhouse gas (GHG) emission. Furthermore, many of these meadows will likely become drier during the growing season in the future because of less precipitation, earlier timing of snowmelt, and increased evapotranspiration associated with climatic warming. To evaluate the potential effects of soil drying on GHG emission, we studied a soil moisture gradient in a Sierra Nevada subalpine meadow in California. Our objectives were: (1) to assess the strength of hydrological control for soil carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes both earlier and later in the growing season; and (2) to quantify the contribution of CH₄ and N₂O to net GHG emission. The replicated gradient spanned 50 m, from the wet middle to dry edge of the meadow, and soil volumetric water content was measured 0 to 12 cm deep. Fluxes of CO₂, CH₄, and N₂O were measured using static chambers at 10 m intervals across the gradient. We found that the wet side of the gradient was not a CH₄ or N₂O source on either sampling date. Net CH₄ emission from soil was rare and CH₄ uptake was prevalent, particularly on the dry side of the gradient. Soil N₂O fluxes shifted from net uptake at the middle of the meadow to net emission at the edge, but only earlier in the growing season. Of the three GHGs, CO₂ fluxes showed the most temporal variation but surprisingly varied little across the hydrological gradient. Other environmental factors—including plant species richness and soil carbon concentration—appeared more important than soil moisture in explaining CO₂ fluxes. Therefore, the strength of near-surface hydrological control increased in the following order: CO₂ < N₂O < CH₄. Our results suggest that non-CO₂ greenhouse gases will need proper accounting during the snow-free season in order to more accurately predict the effects of future soil drying on GHG emissions in heterogeneous montane landscapes.

In the highest land of the Sierra Nevada National Park, an experiment to monitor solifluction rates together with the thermal regime of the ground was implemented during the period 2005–2011. Data show evidence of the low activity of solifluction processes in the present-day periglacial belt of Sierra Nevada. Annual displacement rates were lower than 1 cm yr^-1 both in northern and southern slopes. Solifluction was more active near snow patches and streams. Rates were also higher during snowier years. Soil temperatures showed seasonal frost occurrence, though the depth and duration of the frozen layer is strongly conditioned by the annual snow cover. Water availability appears to be a crucial factor for solifluction processes in this semiarid environment.

The alpine páramo of Chingaza National Park, Colombia, has a highly variable cloud regime typical of many tropical alpine areas. Yet, little information is available regarding the effects of such dynamic sunlight regimes on alpine temperatures. A close association between changes in incident sunlight and corresponding air (T_a) and leaf (T_l) temperatures occurred in two dominant species with strongly contrasting leaf form and whole-plant architecture. Spikes in sunlight incidence of >3000 μmol m^-2 s^-1 occurred during cloud cover and corresponded to increases in T_l of 4–5 °C in a 1-min-interval in both species. Although T_l was predominately above T_a, during the day, depressions below T_a of over 6 °C occurred during cloudy conditions when photosynthetic photon flux density (PFD_s) was <400 μmol m^-2 s^-1. The greatest frequency (69%) of changes in incident sunlight (PFD_s; over 2-min intervals) was less than 100 μmol m^-2 s^-1, although changes >1000 μmol m^-2 s^-1 occurred for 2.4% of the day, including a maximum change of 1512 μmol m^-2 s^-1. These data may be valuable for predicting the ecophysiological impact of climate warming and associated changes in future cloud regimes experienced by tropical alpine species.

Temperature-index models are popular tools for glacier melt-modeling due to their minimal data requirements and generally favorable performance. We examine the effects of temperature forcing provenance and extrapolation on the performance of one such model applied to a small glacier in the Saint Elias Mountains of northwestern Canada. The model is forced with air temperatures recorded (a) on two glaciers, (b) at two nearby ice-free locations, and (c) by two low-elevation valley stations. We extrapolate these temperatures using constant lapse rates and assess model performance by comparing measured and modeled cumulative summer ablation at a network of stakes over five melt seasons. When the model is calibrated individually for each temperature forcing and lapse rate, the variation in model performance is modest relative to inter-annual variations associated with melt-season conditions and calibration data quality. Despite <30% variation in estimated summer ablation arising from the combined influences of temperature forcing and lapse rate, the resulting variations in estimated annual mass balance can be significant (>100% in some cases). While model parameters calibrated in this way suffer from error compensation and exhibit equifinality, the lapse rates associated with minimum model error exhibit inter-annual variation that can be related to prevailing meteorological conditions. When the model is instead calibrated at the point scale without employing a lapse rate, and the resulting parameters are paired with an arbitrary temperature forcing, lapse rates associated with minimum model error vary widely between forcing types and years. Low-elevation stations distal from the study site sometimes outperform the calibration station, but the prescribed lapse rate becomes critical in this case. With either calibration method, lapse rates that minimize model error for the valley stations are generally steeper than the measured environmental lapse rates.

We present ground-penetrating radar (GPR)—based volume calculations, with associated error estimates, for eight glaciers on Wedel Jarlsberg Land, southwestern Spitsbergen, Svalbard, and compare them with those obtained from volume-area scaling relationships. The volume estimates are based upon GPR ice-thickness data collected during the period 2004–2013. The total area and volume of the ensemble are 502.91 ± 18.60 km² and 91.91 ± 3.12 km³, respectively. The individual areas, volumes, and average ice thickness lie within 0.37–140.99 km², 0.01–31.98 km³, and 28–227 m, respectively, with a maximum recorded ice thickness of 619 ± 13 m on Austre Torellbreen. To estimate the ice volume of unsurveyed tributary glaciers, we combine polynomial cross-sections with a function providing the best fit to the measured ice thickness along the center line of a collection of 22 surveyed tributaries. For the time-to-depth conversion of GPR data, we test the use of a glacierwide constant radio-wave velocity chosen on the basis of local or regional common midpoint measurements, versus the use of distinct velocities for the firn, cold ice, and temperate ice layers, concluding that the corresponding volume calculations agree with each other within their error bounds.

Facilitative interactions among plant species enable plant community development under stressful environmental conditions. Previous studies in two treeline communities within the alpine-treeline ecotone on the Rocky Mountain Front in northwestern Montana, U.S.A., indicated that whitebark pine (Pinus albicaulis) serves as the majority tree island initiator, thus facilitating the development of tree islands (Resler and Tomback, 2008). However, 33.7% of whitebark pine at these treeline study sites were infected by the introduced pathogen Cronartium ribicola, which causes white pine blister rust. We examined the prevalence of whitebark pine, its ecological role, and the incidence of blister rust within two study sites, Tibbs Butte and Wyoming Creek, to the south on the Beartooth Plateau, and within two study sites, Stanley Glacier and Gibbon Pass, to the north in Kootenay and Banff National Parks, for comparison with information from the Rocky Mountain Front (Resler and Tomback, 2008). We found that whitebark pine was an important component of treeline communities in both the southern and northern study areas, although its abundance and ecological role varied with study site. Nearly half the solitary trees sampled overall in the northern and southern study areas were whitebark pine. Whitebark pine was also the most frequently occurring conifer species among tree islands at three of the four study sites. Across all study sites, whitebark pine served as tree island initiator for 29.4% of the tree islands sampled, but was a more frequent initiator within two study sites. Blister rust incidence for the Wyoming Creek study site in the southern study area was 7.7%, and for the Stanley Glacier study site in the northern study area, 16.2%. Damage and mortality over time from Cronartium ribicola will diminish the current ecological role of whitebark pine as a facilitator of landscape vegetation pattern development and may confound predictions of upward movement of treeline in response to climate warming.

Tibetan alpine grasslands are viewed to be sensitive to climate change and grazing disturbance. But it is not well understood how and to what extent grazing exclusion affects species assembly on the Northern Tibetan Plateau. We conducted a multisite transect along a precipitation gradient to detect species compositional changes at 25 grazed versus nongrazed paired pastures in summers of 2009 and 2010 in the Changtang Natural Reserve. Species richness and relative frequency were estimated for plant functional groups (PFGs: grasses, sedges, forbs, and legumes). Species richness at community level responds positively to precipitation and differs among vegetation types: meadow (22.63 ± 1.73) > steppe (11.23 ± 1.00) > desert-steppe (6.75 ± 0.63). Variations in species richness and relative frequency of PFGs are partly dependent on vegetation type. Three to four years of grazing exclusion has not significantly changed species richness or relative frequency at PFG level. Grazing exclusion has slightly changed PFGs' correlations in species richness but significantly altered their correlations in relative frequency within and across vegetations. Stepwise linear regressions indicate that PFGs respond to climate gradients in discrete ways. This study implies that specific adaptation mechanisms of different taxonomic groups to climatic change and grazing disturbance should be seriously considered in further studies.

Global temperature increase would seem likely to result in general upwards shifts of altitudinal margins of tree stands. However, range expansion of trees could be significantly affected by both negative and positive interactions with alpine shrubs in existing treeline ecotones. We examined the effects of dwarf pine (Pinus mugo) shrubs on the vegetative propagation and height growth of Norway spruce (Picea abies) trees in the treeline ecotone of the Hrubý Jeseník Mountains, Czech Republic. Here, the non-native dwarf pine was planted above timberline during the 19th and 20th centuries. In the treeline ecotone, vegetative propagation is important both for generation of clonal groups from seed-originated individuals and for persistence of such stands. We found that increasing density of dwarf pine stands strongly reduced vegetative propagation of spruce, as shown by the spruce clonal groups surrounded by dense pine having fewer layering branches and ramets than such groups outside pine stands. This has likely resulted from competitive pressure of pine causing decreased spruce layering mainly through mechanical damage and shading. In contrast, dense pine stands increased spruce height growth, presumably by providing shelter against wind and/or browsing. Our results indicate that interactions of prostrate dwarf pine and Norway spruce clonal groups include both competitive and facilitative components, which probably change in importance along climatic stress gradients.

In order to predict the response of alpine ecosystems to global warming and to provide the experimental data needed for Atmosphere Global Circulation Models (AGCMs) coupled with Land Surface Models (LSMs), a warming experiment using infrared heaters was conducted in the alpine meadow ecosystem of the Qinghai-Tibet Plateau. Five replicate blocks with three 2 × 2 m treatment plots in each block were randomly installed. The treatment plots were control plots (C) at ambient temperatures, moderately warmed plots (W1), and intensely warmed plots (W2), manipulated by using 130 W m^-2 and 150 W m^-2 infrared heaters, respectively. The results showed that when significant warming increased the daily mean soil surface temperature by 1–3 °C compared to temperatures in the control plots during the warm season (seasonal frozen soil thaw), the soil temperature gradients from depths of 0 to 100 cm significantly increased by 0.02–0.04 °C cm^-1 during the day and 0.01–0.03 °C cm^-1 at night. Volumetric soil liquid water content significantly decreased by 2.6–3.4% in shallow soil (5–15 cm) and significantly increased by 0.7–5.1% in deep soil (100 cm) compared to the control plots. Likewise, soil liquid water content gradients at depths between 10 and 20 cm significantly decreased by 0.2–0.3% cm^-1 and significantly increased by 0.01–0.08% cm^-1 at depths between 20 and 100 cm. Warming did not cause significant vapor water change in the atmosphere near the soil surface. Based on these results, it can be concluded that increasing soil temperatures accelerated the processes of ground heat flux, sensible heat, and latent heat, which caused significant change in soil water content and in its gradients.

Soil moisture has widely been identified as a key factor for vegetation distribution in semi-arid areas. In the forest-steppe ecotone of the Khentii Mountains in northern Mongolia, soil moisture is directly controlled by exposition, slope, the presence or absence of permafrost, and vegetation cover. This study investigates the distribution of soil moisture and highlights the effects of a recent wildfire on this fragile ecosystem. Steep southerly exposed slopes are permafrost free and covered with steppe vegetation. Here, relatively warm and dry soils prevail, and high drying rates were observed following precipitation events during the summer period. The less inclined northerly exposed slopes are covered with taiga and feature relatively cold and wet soils overlying permafrost. Following a wildfire, the mean thickness of the organic surface layer drastically decreased from 0.15 m in the pristine taiga to 0.03 m in a heavily burned forest. As vegetation removal directly reduced evapotranspiration, soils in the burned forest were significantly the wettest and soil drying was less pronounced. Simultaneously, permafrost degradation was enhanced due to a significant increase in soil temperature. Thus, the conversion of forest areas to steppe after wildfires appears to be a long-term and possibly irreversible process during the ongoing climatic trend.

While elution processes of ions and solutes from alpine and arctic snowpacks are well known, the scientific knowledge of the effects on microbial cells and their link to glacial surface ecology during this period is very limited. Here we show that dissolved substances are eluted from a High Arctic snowpack according to previous reports, while the microbial cells are retained and most likely also proliferate. Their retention enhances the interaction between the snowpack-derived microorganisms and microbial communities living on the surface of glaciers, a habitat known for its cell retention, especially those associated with debris known as cryoconite. Microbial biomass is retained during all stages of the summer ablation upon these Arctic glaciers, emphasizing the need to explore the feedback between microbial growth and meltwater biogeochemistry. Furthermore, the snowpack stratigraphy at Midtre Lovénbreen, Svalbard, shows a frequently low abundance of cells, typically corresponding to those of cloud water. However, a few layers show higher bacterial numbers (up to 10⁴ cells mL^-1) that occur with an increase of dust particles and most likely originate from local sources.

Thermal regimes of eight periglacial talus slopes, at contrasting elevations, aspects, and substrates, in the Sierra Nevada, California, had complex microclimatic patterns partially decoupled from external conditions. Over three years, warm seasons showed mean talus matrix temperatures and daily variances lower than surfaces and cooler than free-air; talus surface and matrix positions low in the taluses were colder than higher positions, yielding highly positive altitudinal temperature differentials; ground surface temperatures had greater daily extremes than talus positions; and talus matrix temperatures lagged in response to surface temperature changes. Regulating processes in summer include evaporative cooling, cold-air drainage and Balch effect, and shading effects. In the cold season, talus matrices were warmer than surfaces; low talus positions were warmer than high; isothermal zero-curtain periods occurred before snow disappearance; and snow covered talus low positions more often and longer than higher in the taluses, which were often snow-free. Winter thermal processes likely include insulation from snow cover at talus bases, free exchange between talus matrix and external air in the upper talus, and latent heat from thaw-refreezing in late winter. Permanent ice may occur within high elevation talus slopes. Partially decoupled talus thermal regimes provide buffered habitats for mammals such as American pikas and are likely to be important refugia under future warming.

The unavailability of sufficient data at higher elevations causes many uncertainties in research on cold regions. This study considers a cryosphere-hydrology observation system established in 2008 at the Hulu small alpine watershed in the Qilian Mountains of Northwest China. The altitudinal gradient of weather factors is analyzed using data from the Hulu watershed and routine stations located in the Heihe upstream. The data presented here provide the following knowledge of mountain meteorology at elevations from 3367 m to 4166 m/4248 m in the Qilian Mountains: (1) the yearly precipitation—altitude relationship is linear in regions below 4248 m in the Heihe upstream, where the precipitation gradient increased marginally from 1960 to 2011; (2) the yearly air temperature lapse rate (TLR) is weaker at higher elevations (>3000 m), and the seasonal TLR became more divergent between winter and summer half-years from 1960 to 2011 (yearly mean 5.6 °C km^-1); (3) in the Hulu watershed, the LRs of water vapor pressure and absolute humidity are higher in warm seasons with yearly means of 1.1 hpa km^-1 and 0.84 g m^-3 km^-1, respectively, and the maximum relative humidity value is found at elevations between 3500 and 3700 m in the Heihe upstream; (4) the long-term existence of snow increases the albedo to yearly means of 0.22, 0.30, 0.35, and 0.27 in areas of grassland, meadow, marshy meadow, and alpine desert in the Hulu watershed, respectively. The relationship between monthly net radiation and soil surface temperature (Ts) is linear, and the mean Ts LR was about 7.5 °C km^-1 from July 2009 to September 2011.