Holocene changes in terrestrial provenance and processes of sediment transport and deposition are tracked along a fjord-to-shelf transect adjacent to Vestfirdir, Iceland, using the magnetic properties of marine sediments. Magnetic susceptibility (MS) profiles of 10 cores (gravity and piston) were obtained onboard using a Bartington MS loop. Remanent magnetizations were measured at 1-cm intervals from u-channel samples taken from six cores on a cryogenic magnetometer. Between six and nine alternating field demagnetization steps were used to isolate the characteristic magnetization directions. The chronologies of the cores used in this study were determined from AMS ¹⁴C dates on mollusks and foraminifera and constrained by the regional occurrence of the 10,200 ± 60 cal yr. BP Saksunarvatn tephra. Correlative fluctuations in magnetic concentration are noted between the fjord and shelf sites, though these fluctuations are partially masked by regional variations in carbonate content. The onset of Neoglaciation is interpreted by changes in magnetic properties including an increase in mass magnetic susceptibility that began approximately 3000 cal yr. BP. The maximum angular deviation and the median destructive field (generally <20 mT) suggest that the natural remanent magnetization is carried by a coarse ferrimagnetite mineralogy, likely magnetite or titano-magnetite. Reproducible paleomagnetic inclination values are observed in several records, including a nearly vertical inclination around 8000 cal yr. BP, suggesting that the magnetic pole may have been proximal to Iceland, followed by an interval of much shallower inclination (6000–7000 cal yr. BP).

A field experiment was conducted in the Front Range of the Colorado Rocky Mountains to test the hypothesis that lichen age-size curves differ in shape because an inherently sigmoidal growth pattern is interrupted at different stages in its development by a linear growth phase. Large, circular thalli of three morphologically dissimilar species were studied on smooth rock surfaces. Thallus interiors were removed with a knife and wire brush, creating curved wedges of lichen tissue. Distances from reference marks to the unmodified outer margins of the thalli were measured at various wedge widths. Measurements were repeated after 2–16 years, depending upon species. As predicted by the hypothesis, radial growth of Xanthoparmelia coloradoensis and Lecanora novomexicana accelerated with increasing wedge width, becoming linear at average rates of 2.01 and 0.12 mm yr⁻¹, respectively. Radial growth of Rhizocarpon superficiale accelerated to a maximum average rate of 0.016 mm yr⁻¹, then slowed, defining a more complete sigmoidal curve. This species showed no evidence of a linear growth phase, either because none exists or because the wedges were too narrow to detect it. The margins of R. superficiale thalli alternately advance and retreat due to changes in moisture availability and differences in photosynthate production within outer rings of areolate tissue. Hypothalli and areolae grow independently of each other over the short term, though their long-term growth rates must necessarily be similar. The data suggest that areolate crustose lichens are fundamentally different from foliose and placodioid lichens, and that inferences based on one group should not necessarily be extrapolated to another.

This study was part of the International Tundra Experiment (ITEX) and examined the effects of increased winter snow depth and decreased growing season length on the phenology of four arctic plant species (Betula nana, Salix pulchra, Eriophorum vaginatum, and Vaccinium vitis-idaea) and seasonal nitrogen availability in arctic snowbed communities. Increased snow depth had a large effect on the temporal pattern of first date snow-free in spring, bud break, and flowering, but did not affect the rate of plant development. By contrast, snow depth had a large qualitative effect on N mineralization in deep snow zones, causing a shift in the timing and amount of N mineralized compared to ambient snow zones. Nitrogen mineralization in deep snow zones occurred mainly overwinter, whereas N mineralization in ambient snow zones occurred mainly in spring. Concentrations of soil dissolved organic nitrogen (DON) were approximately 5 times greater than concentrations of inorganic nitrogen (DIN) and did not vary significantly over the season. Projected increases in the depth and duration of snow cover in arctic plant communities will likely have minor effects on the rate of plant phenological development, but potentially large effects on patterns of N cycling.

Pollinator-dependent reproductive systems are predicted to be disadvantageous in the Arctic due to the unreliability of pollinator services. Observations in northwestern Alaska appear to support this prediction, where the common Primula eximia possesses reproductive assurance through homostyly and is outpacing the reproduction of its rare, distylous, and pollinator-dependent congener, P. tschuktschorum. We examined the reproductive ecology of these two taxa to determine if P. tschuktschorum is fully distylous with self and intramorph incompatibility, if P. eximia is homostylous with an advantage in fecundity over the rare species, and if there are reproductive interactions between the species. Our results indicate that while P. tschuktschorum is morphologically distylous, it displays only weak incompatibility reactions, but nonetheless has significant reproductive limitations relative to the fecundity of P. eximia, especially in the face of herbivory, which reduces the pool of compatible mates. Some hybridization is occurring between the species. These results support previous suggestions that reproductive assurance may be an important factor limiting the distribution of distyly where pollinator service is unreliable. Homostylous species are likely to be more successful and outcompete distylous progenitors, and selection pressures for reproductive assurance may lessen strong self and intramorph incompatibility reactions in distylous species.

We investigated the effects of experimental manipulations of snowmelt on the flowering phenology and forage chemistry (digestibility and nitrogen concentration) of tussock cottongrass (Eriophorum vaginatum) on the Seward Peninsula, Alaska. Early snowmelt accelerated reproductive phenology by 11 days, and resulted in higher floral digestibility both early and late during inflorescence development. Nitrogen concentrations of inflorescences in late snowmelt plots were initially the highest among treatments, but decreased nearly 40% during inflorescence development. Thus, changes in climate that lead to changes in snow cover can alter both the timing of flowering and chemistry of Eriophorum and, consequently, its value as reindeer and caribou forage. We then used published relationships between forage chemistry and body weight gain of reindeer (White, 1983) to model the possible effects of altered forage chemistry on food intake and growth in reindeer. Model output shows that reindeer foraging on Eriophorum inflorescences may increase digestible dry matter intake twofold by selectively foraging on early-emergent inflorescences. The multiplicative effects of forage quality and food intake result in a near doubling in the rate of weight gain during this critical early spring period. Such increases in body weight gain have potentially great consequences for reindeer at both individual and population levels.

Deposition of atmospheric nitrogen from urban and agricultural sources has caused surface water nitrate concentrations to increase in the Front Range of the Colorado Rocky Mountains. To investigate the effects of sustained increases in nitrate concentrations on phytoplankton dynamics in an alpine lake, we conducted nutrient enrichment experiments in mesocosms amended with nitrate, phosphate, and phosphate plus nitrate on four dates in July and August 2002. During this period, phytoplankton species composition shifted as diatoms decreased in abundance. Phytoplankton chlorophyll a increased in the phosphate and phosphate plus nitrate enrichments, but did not increase in the nitrate only enrichments. Analysis of the phytoplankton community using Principal Component Analysis showed that 34% of the variance was accounted for by the primary axis, which was associated with different time periods, and 21% of the variance was explained by the secondary axis, which was associated with treatments. The response to phosphorus enrichment was taxon-specific, and the two chlorophyte species which became more abundant, Chlamydomonas sp. and Scenedesmus sp., were strongly weighted on the secondary axis. These results indicate that the productivity of this phytoplankton community is phosphorus-limited throughout the summer. Therefore, additional inputs of nitrogen are not expected to directly alter the productivity of the phytoplankton community.

Mammalian herbivores in arctic tundra often alter plant species composition and lichen abundance, with effects dependent on grazing season and herbivore preference. We investigated how long-term mammal exclosures designed to exclude large mammals (caribou) alone, large and medium-sized mammals (e.g., ground squirrels), or all mammals (including voles and lemmings) affected lichen abundance and species composition as well as the vascular plant community. The exclosures were partly established in combination with long-term soil nutrient additions to investigate the interaction between mammal activity and nutrient availability. Our study was conducted in dry heath tundra in northern Alaska, dominated by dwarf evergreen shrubs and lichens. Excluding mammals for 17 years allowed the lichen community to increase in biomass, particularly within the genus Cladonia, which also had more intrageneric diversity in the exclosures; after 10 years, results were subtler. Fertilization, however, almost eliminated the lichens, regardless of herbivore treatment. This coincided with a dramatic shift in vascular vegetation toward a more palatable grass-dominated community, similar to studies of other arctic heaths. Our results suggest that with greater soil nutrient availability that occurs with climate warming, lichens will decrease in abundance, and this effect may be exacerbated by increased mammalian herbivory.

The bogong moth migrates annually to the mountains of southeastern Australia in spring, to estivate at alpine altitudes, before returning to the plains in autumn to breed. Although occurring at low densities in the plains as larvae, when they estivate gregariously densities reach high levels, so that any chemicals carried by them are concentrated. One such chemical is arsenic, which is concentrated to phytotoxic levels in the soils surrounding estivation sites. Vegetation may recover as arsenic is made unavailable by time or by fire. This may be a cyclical process that has occurred many times in the past. Bogong moths are an important food for birds and small mammals, and arsenic has been found in the food chain, although bird deaths and population declines in small mammals cannot be positively ascribed to arsenic. Genetic studies and studies looking at the chemical form of the arsenic have so far been unable to confirm the source of the arsenic; however, interception of moths on their spring migration confirms that the source is away from the mountains.

The Buordakh Massif, in the Cherskiy Range of northeast Siberia, contains mountains over 3000 m and, despite its arid climate, numerous glaciers. This paper presents a glacier inventory for the region and documents some 80 glaciers, which range in size from 0.1 to 10.4 km² (total glacierized area is ca. 70 km²). The inventory is based on mapping derived from Landsat 7 ETM satellite imagery from August 2001, augmented with data from field investigations obtained at that time. The glaciers in this region are of the ‘firn-less,’ cold, continental type, and their mass balance relies heavily on the formation of superimposed ice. The most recent glacier maximum extents have also been delineated, and these are believed to date from the Little Ice Age (ca. A.D. 1550–1850). Glacier areal extent has reduced by some 14.8 km² (ca. 17%) since this most recent maximum. Of the 80 glaciers catalogued, 49 have undergone a measurable retreat from their most recent maximum extent.

Lichen regeneration timelines are needed to establish sound fire management guidelines for caribou (Rangifer tarandus) winter range. Paired burned and unburned permanent vegetative cover transects were established after 1981, 1977, and 1972 tundra fires in northwestern Alaska to document regrowth of tundra vegetation including caribou forage lichens in the wintering range of Alaska's largest caribou herd. Following fire, lichen had recovered very little compared to unburned transects (1% cover vs.15% cover) after 14 years. After 24 or 25 years, lichen cover in the burns remained low (3–4%), whether or not caribou were present during the recovery period. In addition, lichen cover on unburned transects at one study site had decreased from 14% to 6%. Shrub cover was higher on the burned plots than the unburned plots. Cover of cottongrass (Eriophorum vaginatum) initially increased following the fire and tussocks quickly became more vigorous than on paired unburned transects, remaining so for more than 14 years. Persistent changes in vegetation following fire likely reflect the cumulative impacts of seasonal caribou use and favorable growing conditions (warmer soils, longer growing season) for rooted vascular species during the recovery period. The actual recovery of forage lichens after fire on our study sites is slower than predictions based on ideal growth potential.

Nonsorted circles are relatively barren patterned-ground features common in most arctic tundra regions. We studied how vegetation changes on nonsorted circles might affect cryogenic processes, which is of relevance as arctic vegetation responds to climate change. Twenty-eight circles at a moist nonacidic tundra site in northern Alaska received one of four treatments: (a) vegetation removal; (b) vegetation removal and sedge transplants; (c) vegetation removal and moss transplants; or (d) no manipulation. We monitored soil-surface temperatures, thaw depth, frost heave, and soil-surface instability as indicators of cryogenic processes for three years.

Vegetation removal led to 1.5 °C (22.3%) warmer summer soil-surface temperatures, 4.8 cm (6.2%) deeper mean thaw depth, 3.5 cm (26.2%) greater frost heave and a drastic increase in an index of soil instability when compared to the control. In contrast, moss additions lowered soil-surface temperatures by 2.8 °C (41.8%) in the summer, delayed freezing by almost two weeks and thawing by one week, decreased mean thaw depth by 10.3 cm (14.9%), and decreased frost heave by 6.6 cm (52.4%) when compared to the control. The sedge treatment had intermediate effects on thaw and heave. This study indicates that increases in plant cover and particularly moss cover on nonsorted circles due to a warming climate would decrease the heat flux between the atmosphere and the mineral soil and result in shallower thaw and less frost heave, leading to regional reductions in the activities of nonsorted circles.

Consistent with general predictions and earlier empirical studies, it appears that recent climate warming has started to affect large-scale biogeographical patterns in northern Sweden. Long-term, systematic monitoring in permanent altitudinal belt transects reveals spread of broadleaved thermophilic tree species with quite different life histories into the subalpine forest belt. Saplings of Quercus robur, Ulmus glabra, Acer platanoides, Alnus glutinosa, and Betula pendula have responded to altered climatic conditions by jump-dispersal in the order of 50–300 km northwards and 500–800 m upwards. Thereby, they have reinvaded elevations where they grew during the warmest phase of the Holocene, 9500–8000 years ago, but were subsequently extirpated by Neoglacial cooling. Confined to the past 15 years or so, these unique observations are consistent with background climatic data, i.e. warming of all seasons. The results contribute to more realistic vegetation models by stressing that at least certain plant species are able to track climate warming without substantial migration lag.

We investigated the effects of snow and environmental variables on the depths to which moose sank in snow, and the extent to which moose followed in the tracks of other free-ranging moose in the mountains of the subarctic areas of northernmost Sweden. We tested a method to combine the variables that affect snow quality (e.g. density and hardness) into a single variable that is easier to measure in the field. We also studied the snow conditions in the summer and winter ranges of migrating moose. First, we performed correlation analyses that revealed that sinking depths of moose decreased with increasing snow quality, snow depth, altitude, and air temperature. Next, we next used the Akaike information criterion (AIC) to determine the best model of sinking depth, which indicated that the important variables were snow quality, altitude, and snow temperature. For trail-following behavior, the best model included air temperature only. Regarding seasonal ranges, winter ranges had considerably less snow than the summer ranges that these individual moose left, but snow quality did not differ. Overall, our new method to index snow quality (here, using a dynamometer to measure the force required to press a simulated moose foot down in the snow to the depth of a moose footprint) shows promise, and we suggest that future studies of ungulate winter ecology investigate it further.

Soils of the McMurdo Dry Valleys are among the most extreme terrestrial environments, hosting low-diversity food webs of microbes, protozoa, and metazoan invertebrates. Distribution of soil invertebrates, particularly nematodes, is related to the highly variable soil geochemistry of the valleys. Bull Pass is a glacially carved area within the McMurdo Dry Valleys where a broad range of geochemical conditions occurs along a continuous soil gradient. This site provides the opportunity to investigate how soil geochemistry controls nematode distribution on a local scale, and to establish correlations that may also be relevant at regional scales. At Bull Pass, two nematode species were present, with the dominant Scottnema lindsayae occurring in >30% of the samples. There were significant negative correlations between live nematode abundance and soil nitrate concentration and salinity, consistent with experiments showing strong salinity effects on nematode survival. A logistic regression model based on data sets from across the McMurdo Dry Valleys showed a strong negative relationship between soil salinity and the probability of live nematodes occurring. Soil chemistry and nematode distribution from the Bull Pass transect are compared with model results and suggest that the larger-scale distribution of nematodes across the McMurdo Dry Valleys may be reflected in the smaller-scale chemical and biological gradients at Bull Pass.

Understanding natural variability in precipitation and drought, and the resulting effects on Sierra Nevada forests, is crucial for successful resource management in this environmentally sensitive area of California. This study assessed the species-specific influence of precipitation variations on radial growth, recruitment, and mortality patterns for three conifer species (Pinus jeffreyi, Juniperus occidentalis, and Pinus contorta) in two mid-elevation lake catchments over the past 550 years. The P. jeffreyi chronology was the most highly correlated with winter precipitation patterns, although the other two species also exhibited significant correlations. Ring-width patterns suggest the influence of the Pacific Decadal Oscillation (PDO) and El Niño–Southern Oscillation (ENSO) on winter precipitation over the length of the records. Recruitment patterns displayed significant, though directionally distinct, correlations with winter drought: P. contorta exhibited increased recruitment during extended drought periods, while P. jeffreyi and J. occidentalis showed increased recruitment during wetter intervals. Finally, a ring of dead trees around both lakes is evidence of a late 20th century water level rise, likely caused by earlier snowmelt and/or wetter conditions. Moisture availability has exerted a strong influence on Sierra Nevada forests through time, but the strength of tree-growth response, and even the sign of tree population response, has been species-specific.

Seasonal variations in ablation and surface velocity were investigated on the lower part of Fox Glacier, South Westland, New Zealand. A large variation between summer and winter ablation was recorded, with daily averages of 129 mm d⁻¹ and 22 mm d⁻¹, respectively. Variations in measured climatic variables were found to account for ∼90% of variation in ablation during both summer and winter seasons, with significant increases in ablation occurring in conjunction with heavy rainfall events. Surface velocity also showed seasonality, averaging 0.87 m d⁻¹ during summer and 0.64 m d⁻¹ in winter, a reduction of ∼26%. It is thought that the general reduction in velocity during winter can be attributed to a decrease in the supply of surface meltwater to the subglacial zone. Short-term velocity peaks appeared to coincide with heavy rainfall events, with surface velocity responses typically occurring within 24 hours of each rainfall event. During winter, moderate rainfall events (≤100 mm over 24 hours) created a surface velocity response up to 44% greater than the prevailing velocity. Though difficult to deconvolve, magnitudes of surface velocity response to rainfall inputs appear linked to time lags between rainfall events and subglacial drainage efficiency and water storage. The longer-term dynamics of Fox Glacier appear linked to fluctuations in the Southern Oscillation Index (SOI), with positive mass balances of Southern Alps' glaciers appearing to mirror negative SOI (El Niño) conditions. Given the calculated response time of ∼9.1 years for Fox Glacier, the current terminus advance may be linked to mass gains reported in the mid-1990s, with current mass balance gains perhaps leading to terminus advances ∼9 years hence.

Natural snow avalanches have periodically damaged infrastructure and disrupted railroad and highway traffic at the southwestern corner of Glacier National Park, Montana. The 94-year history of these disruptions constitutes an uncommon record of natural avalanches spanning over nine decades and presents a unique opportunity to examine how natural avalanche frequency and minimum extent have varied over time due to climatic or biophysical changes. This study compared the historic record of natural avalanches in one avalanche path with tree-ring evidence of avalanches from 109 cross sections and increment cores collected in the same path. Results from combined historic and tree-ring records yielded 27 avalanche years in the 1910–2003 chronology, with the historic record alone underestimating avalanche years by half. Mean return period was 3.2 years. Interpolated maps allowed for more spatially precise estimates of return periods throughout the runout zone than previous studies. The maps show return periods increase rapidly downslope from 2.3 to 25 years. Avalanche years were associated with positive Snow Water Equivalent anomalies at a nearby snow course. Minimum avalanche extent was highly variable but not associated with snowpack anomalies. Most avalanche years coincided with years in which the mean January–February Pacific Decadal Oscillation (PDO) and El Niño–Southern Oscillation (ENSO) 3.4 indices were neutral. The findings suggest that changes in Pacific climate patterns that influence snowfall could also alter the frequency of natural snow avalanches and could thus change disturbance patterns in the montane forests of the canyon.

Whitebark pine (Pinus albicaulis), an important treeline conifer in northern Montana, is considered both a keystone and foundation species in high-elevation ecosystems. The introduced fungal pathogen Cronartium ribicola, which causes white pine blister rust, has resulted in severe declines in whitebark pine in subalpine forest communities throughout the northern Rockies during past decades. However, the prevalence of blister rust in whitebark pine within the alpine treeline community and its impact remain to be determined. We gathered field data on blister rust infection incidence in the treeline ecotone at two locations east of the Continental Divide in the northern Rocky Mountains, Montana, U.S.A. Our objectives were (1) to examine the potential importance of whitebark pine in tree island formation, (2) to determine if blister rust is present in whitebark pine within the alpine treeline community, and (3) to characterize the incidence and intensity of blister rust in krummholz tree islands. We found that whitebark pine is the primary initial colonizer in tree island formation, indicating that the species is important in generating vegetation pattern in these communities. Thirty-five percent of all sampled whitebark pine were infected with blister rust. Although more cankers were found in solitary whitebark pine trees, highest infection incidence per tree occurred in trees that were part of multitree islands. Finally, we found a significant correlation between tree island length and infection incidence. These results have important implications with respect to alpine treeline dynamics on a landscape scale, especially in the context of climate change.

In order to follow the uptake and allocation of N in different plant functional types and microbes in two tundra ecosystems differing in nutrient availability, we performed a ¹⁵N-labeling experiment with three N forms and followed the partitioning of ¹⁵N label among plants, microorganisms and soil organic matter. At both sites the deciduous dwarf shrub Betula nana and the evergreen Empetrum hermaphroditum absorbed added ¹⁵N at rates in the order: NH₄ > NO₃⁻ > glycine, in contrast to the graminoid Carex species which took up added ¹⁵N at rates in the order NO₃⁻ > NH₄ > glycine. Carex transported a high proportion of ¹⁵N to aboveground parts, whereas the dwarf shrubs allocated most ¹⁵N to underground storage. Enhanced ¹³C in Betula nana roots represents the first field evidence of uptake of intact glycine by this important circumpolar plant. Plant and microbial uptake of label was complementary as plants took up more inorganic than organic N, while microbes preferred organic N. Microbes initially took up a large part of the added label, but over the following four weeks microbial ¹⁵N decreased by 50% and most ¹⁵N was recovered in soil organic matter, while a smaller but slowly increasing proportion was retained in plant biomass.

How the carbon balance of arctic ecosystems responds to climate warming will depend on the changes in carbon assimilation capacity of tundra plant species. Along with air and soil warming, one of the consequences of warming likely to be important for carbon assimilation of tundra plant species is an expected 40% increase in growing season length. We examined the effects of a lengthened growing season and soil warming on the photosynthetic capacity of seven tundra plant species from four growth forms that comprise >90% of the vascular cover of wet tussock tundra. Maximum photosynthetic capacity of these key species was relatively unchanged by the manipulation that significantly altered growing season length, active layer depth, and soil temperatures. Highest photosynthetic rates were found for the forb, Polygonum bistorta, and the lowest for dwarf evergreen shrubs. Seasonal patterns revealed that plants maintained relatively high light-saturated photosynthetic capacity (A_max) values throughout most of the growing season. Interannual variation was significant, but differences were small for most species. The study shows that tundra species operate within a relatively narrow range for maximum photosynthetic capacity with this maximum seldom being reached under ambient conditions. Thus, when evaluating the effects of climate change on tundra ecosystem carbon uptake, species composition and total photosynthetic leaf area should be considered first. These two factors will affect the system carbon exchange capacity during climate warming more so than species-level assimilation capacity.

The combined effects of multiple ecological stressors determine the net impact of global change on environmentally sensitive alpine and polar environments. For example, climate warming and nitrogen deposition both increasingly affect ecosystems at high elevations. We hypothesized that the net impact of warming and nitrogen on alpine plankton differs between consumers and producers because of the greater environmental sensitivity of higher trophic levels. Also, we expected that habitat conditions would mediate the responses of plankton to these two stressors as sediments function as ecological buffers against environmental change. These hypotheses were tested in a growth chamber by applying temperature (8 vs. 15°C) and nitrogen (200 vs. 1000 µg N L⁻¹) treatments to a planktonic alpine community in the presence and absence of sediments obtained from Pipit Lake, Banff National Park, Alberta. A significant nitrogen-temperature interaction affected phytoplankton abundance because the positive effect of fertilization depended on warming. Warming also amplified the effect of nitrogen on herbivores while suppressing the fecundity of omnivores. The presence of sediments suppressed the positive effect of warming on herbivores, but stimulated omnivores. The observed prevalence of non-additive effects highlights the strong potential for global change causing future ecological surprises in alpine environments.

Glacier retreat has been widespread on Heard Island, an isolated 2745-m-high volcano in the southern Indian Ocean, since the first observations in 1947. This study represents the first quantification of the mass loss of a Heard Island glacier. Brown Glacier is 4.8 km long and is land terminating. A digital elevation model for the glacier was developed using a combination of static and kinematic differentially corrected GPS surveys and hand-held GPS elevations, and together with ground penetrating radar, was used to estimate the glacier's catchment area boundary. The 1947 extent of the glacier was estimated from an aerial photograph. The total ice covered area has decreased from an estimated 6.18 × 10⁶ m² in 1947 to 4.38 × 10⁶ m² in 2004. This corresponds to a loss of ∼29% of the original area. During the same period the ice volume decreased by an estimated 1.743 × 10⁸ m³ (∼3.06 × 10⁶ m³ a⁻¹), equating to an average thickness change of −0.50 m a⁻¹. The mass loss is consistent with limited temperature observations in the area that indicate a 0.9 °C warming over the same time span. Meteorological observations combined with an energy balance model demonstrate the impact of foehn winds on the mass balance of the upper slopes of the glacier. Between December 2000 and December 2003, repeat differentially corrected GPS surface surveys revealed an average surface change of −9.9 m in the ablation area and −5.9 m in the accumulation area, translating to an ice loss of ∼8.0 × 10⁶ m³ a⁻¹, or more than double the 57 year average rate. There is no indication of an increase in geothermal heat flux that could explain an ice loss of this magnitude. The increase in the rate of ice loss suggests the glacier is reacting to ongoing changes in climatic conditions rather than approaching steady state.

We analyzed lichen species composition and biomass in 815 plots on 163 sites across wild reindeer regions in Norway, ranging from ranges with a long history of very low grazing pressure to heavily grazed sites. Reindeer density (1974–2000) and lichen biomass were well correlated for sites with comparable snow cover, altitude and terrain (R²  =  0.81, P  =  0.006, n  =  12). Absence of grazing for potentially several centuries has virtually resulted in a monoculture consisting of Cladina stellaris, Flavocetraria nivalis, and Alectoria ochroleuca (Syn. Bryocaulon ochroleuca). Light grazing in terms of 20 to 30% removal of initial lichen cover easily eroded Cladina stellaris from exposed ridges by cratering and trampling by reindeer through the snow, while Flavocetraria nivalis persisted longer. This decline in lichen cover observed along a historic grazing gradient further resulted in increasing cover of bare ground, but less than expected from lichen removal due to gradual colonization of other species, such as mosses (incl. Polytrichum piliferum), crustose and fruticose lichens, dwarf shrubs (Arctostaphylos spp., Empetrum nigrum, Loiseleuria procumbens), and graminoids, particularly rushes (Juncus trifidus). Moderate grazing may thus increase plant diversity on ridges compared to ungrazed lands, and hence strongly influence gradients in biomass, composition and abundance of ridge communities across the landscape.

Tree growth is generally limited by temperature in cold climates and by water availability in arid zones. Establishment in altitudinal treeline ecotones depends on the temperature, but may be very sensitive to water availability as well. We studied the effect of climate and land use on the colonization and growth of Pinus cembra in the treeline ecotone of the dry Central Swiss Alps; one site was influenced by timber harvest and cattle activity and another one was undisturbed. Stands were sampled at three elevations: in the forest and the lower and upper parts of the treeline ecotone. The age structure was similar in all sites, ranging from uneven-aged (forest) to more even-aged, with recent densification and upslope expansion of the treeline ecotone. However, recruitment started at the treeline around 1850 (the end of the Little Ice Age) in the undisturbed site, simultaneously with an increase of tree-ring growth, but about 60 years later at the other site, after cattle grazing decreased. These results, and the positive correlation of radial growth with summer and previous autumn temperatures indicated that, in this altitudinal treeline ecotone, growth and establishment are mainly linked to temperature. However, drought stress was visible in the lowest stands, with a positive correlation of growth with rainfall during the previous autumn and December, and in August of the growing season. This could limit growth in a future warmer climate.

Populations of arctic-alpine plant species inhabit a range of environments, to which their life-history characters are expected to have adapted; yet geographic differentiation among populations is seldom studied. Brief growing seasons mean that germination characters are critical fitness traits, especially for annual species. In this study, striking differences in germination traits among three geographically distinct populations of the widely distributed arctic-alpine annual Koenigia islandica are found. The seeds (achenes) of the Colorado population, which experience the lowest summer temperatures, are conditionally dormant; only scarification breaks dormancy. This germination pattern is consistent in all four investigated subpopulations from Colorado, with no significant differences among them. In contrast, seeds originating in the Yukon, which experience extreme winter temperatures but a relatively warm summer, germinate readily after cold stratification, a pattern consistent with that of summer annuals. Seeds from the Norway population, which experience the mildest climate, germinate readily even if untreated. Cold stratification decreases germination fraction in the Norway population, a pattern characteristic of winter annuals. The strong population differentiation found here provides evidence for divergent selection operating among arctic-alpine habitats and suggests that further investigation of its adaptive significance is merited.

New Zealand high-altitude tree limits are formed either abruptly by evergreen Nothofagus or by low forest of more frost-tolerant small trees reaching similar maximum altitudes. Whereas most tree limits are contiguous with low-growing alpine vegetation, in New Zealand a belt dominated by tussock grasses intervenes that is vulnerable to invasion by hardy introduced trees and seems ecologically equivalent to fire-maintained high-altitude tropical grasslands. New Zealand tree limits coincide with warmer growing-season temperatures than other tree limits, including deciduous Nothofagus in the southern Andes. They also correlate with coldest-month mean temperatures around 0°C, in accordance with the limits of broadleaved evergreen trees globally, unlike north temperate subalpine trees that withstand extreme winter cold. Adverse environments lead to krummholz that in temperate regions can form an attenuated belt above the forest limit, but in New Zealand Nothofagus krummholz develops only at or below the forest limit, in accordance with absence of Nothofagus seedlings beyond a few meters above the forest limit. The relatively low altitudes attained by New Zealand trees are related to isolation and the recent uplift of high mountains, and the differentiation between Nothofagus forest and low forest reflects historical and geological events.

Several members of the vascular plant genus Saussurea, which are found at elevations exceeding 5000 m, have dense layers of woolly trichomes on their leaves, bracts, and inflorescences, the function of which is not fully understood. Here we explore the thermal benefits of pubescence in Saussurea medusa, both in situ in the Chinese Hengduan Mountains and under controlled conditions. Mean daytime inflorescence temperature was 5.9 K above air temperature. Pubescence removal revealed that most of this warming is not related to pubescence but to radiant warming of the compact inflorescence itself (4.1 K warming in shaved plants, i.e. 1.8 K less). The effect of pubescence on nighttime radiative cooling was negligible. Our data indicated that the functional role of pubescence in these high-elevation plants cannot be attributed solely to producing warming tissues, but may also include other functions such as water repellency and reflection of short peaks of high radiation. These other functions must be specific to a small group of species, given that most other high elevation taxa do not exhibit this woolly character.

This study attempts to model alpine tundra vegetation dynamics in a tundra region in the Qinghai Province of China in response to global warming. We used Raster-based cellular automata and a Geographic Information System to study the spatial and temporal vegetation dynamics. The cellular automata model is implemented with IDRISI's Multi-Criteria Evaluation functionality to simulate the spatial patterns of vegetation change assuming certain scenarios of global mean temperature increase over time. The Vegetation Dynamic Simulation Model calculates a probability surface for each vegetation type, and then combines all vegetation types into a composite map, determined by the maximum likelihood that each vegetation type should distribute to each raster unit. With scenarios of global temperature increase of 1 to 3°C, the vegetation types such as Dry Kobresia Meadow and Dry Potentilla Shrub that are adapted to warm and dry conditions tend to become more dominant in the study area.