This article describes a 6-yr study of the radial growth rates (RGR, mm yr⁻¹) of Rhizocarpon section Rhizocarpon thalli on a talus slope at Snoqualmie Pass in the Cascade Range, Washington State, United States (47°27′N; 121°26′W). At the end of the growth period, 32 of a total of 39 thalli had exhibited a positive RGR, and 7 of a total of 39 thalli showed no measurable growth. Mean RGR of all thalli was 0.07 mm yr⁻¹ (range, 0–0.19 mm, SD = 0.06). Analysis of variance suggested no significant variation in RGR in successive growth periods, but significant differences were present both within and between thalli. The slope of a boulder facet did not influence RGR, but growth was affected by aspect, the least growth being observed on north-northwest facets. A plot of RGR against thallus diameter revealed a wide scatter of data points with little evidence for a significant change in growth with thallus size. Hence, the study showed that the RGR of Rhizocarpon thalli at Snoqualmie is extremely slow and highly variable and significantly less than estimates based on lichenometry. To determine the growth curve of a yellow-green Rhizocarpon by direct measurement at such a site would require a large sample of thalli and careful standardization of the species studied, the aspect conditions under which the thalli were measured, and the initial hypothallus width of the thalli.

Glacial mapping combined with cosmogenic exposure dating provides the first detailed assessment of the late Pleistocene glacial history in the northeastern Brooks Range, Alaska. Former ice limits were identified in the Okpilak, Jago, Aichillik, Egaksrak, and Kongakut River valleys. Relative-weathering data support our correlations with the well-studied glacial sequence of the central Brooks Range. Of the 16 boulders from four moraines analyzed for ¹⁰Be, the exposure ages on two moraines are tightly clustered. The results indicate that the glacier in the Jago River valley reached its maximum extent during the Itkillik II glaciation by about 23.2 ± 2.8 ka. The ice retreated rapidly, and a prominent, but local, readvance took place by 19.1 ± 2.8 ka within a tributary valley. The relative size of glaciers and the difference in ice extent between the Itkillik I and Itkillik II glaciations varied among the river valleys, with the Aichillik River valley showing the greatest difference. A first-order trend surface fit to Itkillik II equilibrium lines rises toward the south, from 1400 to 1800 m. This is a reversal of the overall trend across the rest of the Brooks Range, and suggests that glaciers of the last glacial maximum in the northeastern sector, similar to today, benefited from the cold and possibly moister conditions associated with their proximity to the Beaufort Sea.

Stone fences and blinds built by prehistoric hunters to gather and ambush elk and bighorn sheep above timberline in the Colorado Front Range are similar in concept and function to structures built by the Copper Inuit and their predecessors for hunting caribou near Bathurst Inlet, in the Central Canadian Arctic. Four principal differences exist: (1) Circular blinds and continuous rock walls are more numerous in the Front Range than in the Arctic, where arcuate breastworks and lines of widely spaced cairns predominate. Differences in prey-species behavior are the most probable explanation. (2) Stone house foundations, meat-drying facilities, meat caches, kayak-storage racks, and fox and wolf traps occur near drive sites along caribou migration routes in the Bathurst Inlet region. The structures imply long-term habitation made possible by a plentiful meat supply. Comparable structures are absent above timberline in the Front Range because people retreated to warmer environments in winter, and because steep terrain and deep snow discouraged return visits to high-altitude caches. (3) The technique was adopted much earlier in Colorado than in the Central Canadian Arctic. The oldest Front Range drive systems were constructed while the Laurentide Ice Sheet still covered the Bathurst Inlet landscape. (4) Pedestrian game-drive hunting was abandoned in the Front Range soon after arrival of the horse (ca. a.d. 1700), but remained an integral part of Copper Inuit subsistence until the mid twentieth century. The rich ethnographic and oral history record of communal hunting in the Arctic is invaluable for interpreting the Colorado structures.

Earth hummocks constitute the most common surface structures of Arctic regions. In hummock tundra ecosystems, small mounds of earth alternate with depressions, the so-called interhummock areas. This study aimed at elucidating how differences in microtopography and associated variations in abiotic and biotic factors control biogeochemical cycles in hummock tundra soils. We assessed N pools and N transformation rates in hummocks and interhummock areas in the southern tundra subzone and along a soil-moisture gradient in the typical tundra subzone of the Taymyr Peninsula, Siberia, Russia. On a regional scale, N pools and transformation rates were positively related to latitude and therefore to temperature. Generally, wetter or waterlogged soil conditions tended to decrease gross mineralization rates and soil microbial N at least in interhummock areas. In contrast, at small spatial scales, soil microclimatic conditions were not the main determinant of the observed nitrogen cycling pattern. We found higher N pools and N gross mineralization rates at interhummock areas (wetter and cooler) compared to the hummocks (warmer and drier). The observed differences in N cycling between microsites of hummock tundra may be the consequence of different plant-cover and variable substrate inputs resulting from differences in microrelief.

Despite an increasing interest in the study of functional diversity, there have been few attempts to link plant traits, habitat variation, and community structure in Alpine landscapes. These interrelationships were examined along a snowmelt and growing-season-length gradient determined by mesotopographical variations. The study site was chosen so as to encompass much of the floristic beta diversity encountered at the Alpine belt of the southwestern Alps. A three-table ordination technique, named RLQ, was used to unravel on a quantitative basis the co-structure of a plot-by-environmental-variable table, a plot-by-species table, and a species-by-traits table. The main covariations between traits and habitat were (1) an increased specific leaf area (SLA) and leaf nitrogen content on a mass basis (N_mass) in late-meting sites, (2) a trend toward upright and thick leaves in the most exposed, physically disturbed, early-melting sites, and (3) an increasing leaf area in the middle of the gradient, which also exhibits small-scale disturbance due to the Alpine marmot. The interplay of intermediate snow-melting dates and intense zoogenic disturbance appears to promote plant diversity and the persistence of species whose mean-elevation distribution is located much below the study site. The adaptive value of trait attributes along the mesotopographical gradient is discussed within the broader context of plant strategies in temperate Alpine grasslands.

The modifications of humus characteristics as a result of the establishment and the increasing cover of Rhododendron ferrugineum L. (Ericaceae) in a subalpine meadow were studied in three sites in the northwestern French Alps corresponding to a west–east transect between wet and dry Alps (“Chaîne de Belledonne,” “Massif du Taillefer,” “Briançonnais”). The physical and chemical parameters of humus and biological parameters were studied during the successive studies.

As opposed to other Ericaceae heathlands on siliceous soils (Vaccinium sp., Erica sp., Calluna vulgaris), with an increasing Rhododendron cover, the humus structure changed while some other parameters remain stable or increased. The development of Rhododendron populations on calcareous soils (Briançonnais) with maintenance of a calcareous humus has never been checked before.

The modifications of the Rhododendron environment under its canopy led to an improvement in its growth conditions (positive feedback).

The pedogenesis and interactions among soil, vegetation, and snow cover of four alpine snowbeds on silicate rocks in the Upper Engadine (Central Alps, Switzerland) were investigated. The long-lasting snow cover of snowbeds causes differences in pedogenesis and soil properties compared to adjacent alpine sward. Because of the drainage characteristics of the silicate parent material, pedogenesis of snowbeds varies. On well-drained parent material, percolating meltwater favors podzolization during snowmelt. On less permeable parent material, meltwater causes temporarily water-logged conditions. Thus, the snowbed soils show redoximorphic features such as iron concretions. Snowbed soils are classified as Inceptisols or Entisols. A more detailed differentiation is only possible at the soil family level. Outside the snowbeds, moder humus forms (Rhizic Leptomoder, Rhizic Mullmoder) are common, whereas inside the snowbeds, mull humus forms (Rhizomull) as well as moder humus forms (Leptomoder) occur.

Two large suspended sediment concentration (SSC) pulses were recorded in 1998 in a small snowmelt-fed stream on Ellesmere Island in the Canadian High Arctic. The largest pulse occurred from 7 to 8 July, when 32% of the monitored seasonal sediment transport occurred in only four hours. SSC reached 83,760 mg L⁻¹, exceeding all previously recorded values from high arctic glacially-fed and snowmelt-fed rivers by more than one order of magnitude. The event occurred after the majority of snow in the watershed had melted, and was preceded by a long period of relatively high air temperature, and a small rainfall event on 7 July. We consider the most likely cause of the event to be a rapid mass movement.

Variations in the timing and duration of seasonal snow cover have a significant impact on local and regional atmospheric dynamics, hydrologic and geomorphic processes through the modification of the surface-radiation balance and the ultimate effect on near-surface-air temperature. This study investigated numerically the effect of variations in the date of seasonal snow-cover disappearance on the components of surface-energy balance on the Alaskan North Slope by using a heat-transfer model with phase change. The baseline inputs for the meteorological characteristics included mean daily air temperature, dew-point temperature, snow-cover depth, incident solar radiation, wind speed, and atmospheric pressure observed at Barrow, Alaska, from 1995 to 1998. Three simulation cases were conducted by using the measured snow data and by varying the snowpack-disappearance date by 10 days in 1998. The mean differences of the components of surface-energy balance caused by variations in snowpack disappearance were also quantified on an annual basis from July 1997 through June 1998. Results indicate that varying the snowpack-disappearance date by 10 days in spring can strongly affect the mean annual net solar radiation, sensible heat flux, and latent heat flux and can slightly affect the mean annual net longwave radiation and conductive heat flux.

We have reconstructed a continuous high-resolution penguin population record over the past ∼1300 years from the geochemical and ¹⁴C dating data in the ornithogenic lake sediments at Ardley Island in the Antarctic. The concentrations of F, P, Sr, Se, S, Cu, Zn, and Ca in the sediments are notably enriched and significantly correlated with each other, and they have a consistent pattern of change versus depth. These elements, as previously reported, are biomarkers of penguin droppings and population. Over the past ∼1300 years, the penguin population at Ardley Island, as measured by these biomarkers' concentrations, has a decreasing trend, especially during the past century when the penguin population has dropped steeply. Compared with the paleoclimatic records and glacial advance and retreat history in the study area, the pronounced penguin population changes in the absence of human activities appear to be related to climatic changes. The steep decline of the penguin populations in the past century, however, seems to be caused by the abnormally warming climate in the Antarctic Peninsula.

Spatio-temporal gradients between ecosystems of the central Norwegian high mountains are analyzed. Complex landscape ecological site analyses combined with intensive pitfall trapping are carried out in four investigation areas in two regions. Key questions are addressed for the differences among ecosystems along a broad-scaled oceanic-continental gradient. The answers are based on ecological process analysis and mapping of zoocoenoses in small catchments of two alpine altitudinal belts. A comparison of four ridge sites is presented by analyzing water and temperature balance and activity of arthropods during the driest summer month. The results do not implicate summer drought and heat as limiting factors; summer wetness and cooling are most decisive. Landscape ecological processes, like the accumulation of snow during winter, snow melting, freeze-thaw action, percolation, soil moisture variation, and temperature regimes are exemplified by long-term measurements throughout the year in a small catchment in continental eastern Norway—the driest mountain region in Scandinavia. To learn about the organization and diversity of zoocoenoses, epigeic arthropods (Araneae, Carabidae) are investigated along spatial gradients. Interrelations between distribution patterns of animals and spatio-temporal dynamics of the environmental conditions are presented. The results are framed by gradient theory in landscape ecology. Finally, the complexity of spatio-temporal gradient determination between ecosystems is discussed and summarized by a scheme of gradient principles for the Norwegian mountains.

A pollination network of 26 pollinator species interacting with 17 plant species from the small Greenlandic island Uummannaq was analyzed for multiple parameters values. Of the insects collected, 77% of all individuals and 77% of all species belonged to Diptera. The ratio of pollinators to plant species was 1.5, which is lower than in other Arctic pollination networks. This might be a double-island effect as Uummannaq is a small island next to Greenland. Connectance was 14.3%, and linkage level of pollinator and plant species averaged 2.4 and 3.7 species links, respectively. The characteristic path length and average clustering coefficient of the 1-mode networks were 1.4 and 0.83, respectively, for the pollinator species and 1.3 and 0.79, respectively, for the plant species. For both pollinator species and plant species, the tail of the degree distribution had the best fit to an exponential model, indicating that the most connected species was constrained in their linking. However, the extremely short path length and high clustering indicated that the networks had small-world behavior, meaning that any disturbance is spread very fast to the entire network and that the networks are error tolerant but vulnerable to attack on the most linked species.

The study presented herein investigated the differences in stand structure of grazed and ungrazed subalpine forests and whether subalpine forests used for grazing satisfactorily protect against avalanches. In subalpine forests of Picea abies L. Karst and Larix decidua Miller, grazed and ungrazed plots of 225 m² were analyzed through the use of dendroecological methods. The grazed forests were found to be less dense than the ungrazed forests and to have a higher percentage of European larch. However, the density of the forests investigated was high enough to impede the release of avalanches. The young trees grew faster in the grazed forests. There were less dominant trees in grazed forests, and these trees were much older than in ungrazed forests. The main structure types in the grazed and ungrazed forests were multilayered open and uniform dense, respectively. The management of mountain forests as wood pastures seems to enhance the readiness of the forest owners to conduct selective logging operations. Thus, forest grazing can encourage the development of heterogeneously structured forest stands, which can regenerate more easily while fulfilling a function of avalanche protection.

Carbon dioxide (CO₂) concentration under snow was examined through two winter seasons at a 3100 m elevation subalpine site in the Snowy Range of Wyoming. CO₂ was monitored every half hour at the soil/snow interface, and at about −25 cm soil depth the second year, in a meadow and in an adjacent forest. CO₂ under snow in the meadow was significantly higher than that in the forest. CO₂ at −25 cm depth in the soil was significantly higher than soil surface CO₂. The CO₂ under snow increased rapidly as snow melted and snowmelt began in the spring. CO₂ concentration under snow depended primarily on amount occurring during the previous 24 or 48 h. However, CO₂ concentration was related to snow depth and soil temperature, and indirectly to several seasonal environmental factors, especially solar radiation. Solar radiation, snow depth, and CO₂ under snow all increase concurrently as the winter season progresses. CO₂ flux was consistently higher in the meadow than in the forest and increased in late winter for both sites. Snow covered subalpine meadows and forests contribute considerable amounts of CO₂ to the atmosphere in the winter.

This paper deals with the floristic structure and plant-community composition in relation to environmental gradients in the Tso Kar basin, an ∼300 km² area of the Changthang plateau. A total of 131 sites covering various landscape units—namely, sandy plains, marsh meadows, moist meadows, scrub steppe, fell-fields, and stream courses—were intensively sampled by using random quadrats of 1 m². In addition, these sites were searched for the presence of other vascular plants. In all, 232 species of vascular plants belonging to 38 families and 101 genera were collected and recorded from the study area. Poaceae (39 species), Asteraceae (27 species), Cyperaceae (25 species), Brassicaceae (14 species), Fabaceae (12 species), and Ranunculaceae (12 species) are the dominant families. It is interesting to note that the study area has a very high monocot:dicot ratio (1:2). Analysis of Raunkiaer's life-forms reveals that the area is dominated by two growth forms—namely, 57% hemicryptophytes (perennial grasses and sedges) and 24% chamaephytes (dwarf herbs and matted shrubs). The density of stems ranges from 28 to 744 plants per square meter. Species richness varies from 4 to 15, and diversity values are from 0.143 to 1.679. Among communities, the highest similarity (57.5%) is between Scirpus-Carex and Scirpus-Kobresia-Ranunculus. Conservation implications of the findings and the need for a participatory approach of the rangeland management are discussed.

The response of high arctic ecosystems' carbon dioxide exchange to changing climate is uncertain and may be important from a climate-change perspective. In this study, the net ecosystem carbon dioxide exchange during four growing seasons is examined by combining measurements and modeling from a high arctic fen in northeastern Greenland. The summer-season net ecosystem exchange shows large interannual variations, fluctuating from an uptake of −50 g C m⁻² to −123 g C m⁻². Through ecosystem modeling, we can observe that leaf area index development and the maximum Rubisco capacity are more important controls on the interannual variability of net ecosystem carbon dioxide exchange than meteorological conditions. Furthermore, we present a hypothesis linking the interannual variability in maximum Rubisco capacity with leaf nitrogen content and leaf area index development. This hypothesis may provide a method to model seasonal net ecosystem carbon dioxide exchange in detail without having to resort to elaborate fitting procedures using measured carbon dioxide flux data.

Alpine lakes are often highly transparent to ultraviolet (UV) wavelengths, which has led to the suggestion that a deep chlorophyll maximum (DCM) results in these systems from UV avoidance by phytoplankton. However, an alternative explanation is that the formation of the DCM is primarily driven by greater nutrient availability below the thermocline in these oligotrophic systems. We investigated the location of the chlorophyll maximum over spatial and temporal scales in a set of high-elevation lakes in the Beartooth Mountains (Montana/Wyoming). The position of the DCM was compared to a suite of physical and chemical variables across systems. Chlorophyll was strongly correlated to a suite of nitrogen variables, whereas correlations with UV parameters were not consistently observed. We also conducted an experiment with the natural phytoplankton assemblage from the DCM in Beartooth Lake; both UV exposure and nutrient additions were tested in a factorial design. The UV-exposed treatment and the control had the same final total phytoplankton biovolume, while the nutrient addition treatment had a final biovolume ten times as great. These results suggest that, as in other oligotrophic aquatic systems, greater nutrient availability in the hypolimnion leads to the development of the DCM in alpine lakes.

This paper presents data derived from extensive rockfall investigations in the Karwendel Mountains and in the Ammer Mountains near the German-Austrian border. The rock faces in the areas investigated consist of Mesozoic limestone and dolostone. The debris was quantified by means of more than 60 rockfall collectors, which were emptied regularly. Air and rock temperature data were measured by a meteorological station and by several dataloggers equipped with pT100 temperature probes.

The temporal distribution of rockfall was highly variable, which is due to the combination of several trigger parameters. A statistical analysis of the dataset revealed that various meteorological conditions enhance the probability of rockfall occurrence. Deep frost in winter, freezing and thawing during wet weather conditions, and wetting/drying contribute to the weathering of the rock faces investigated. The actual removal, leading to rockfall, is triggered by a complex combination of frost shattering, temperature fluctuations, and downwash by precipitation. Despite the irregular patterns, it is evident that the mean removal in the summer months is much higher than in winter, which is probably due to the lack of water in the cold season. Even a large number of temperature oscillations across zero do not seem to affect weathering as long as there is an insufficient moisture supply.

Recovery of tall alpine herbfields from livestock grazing and drought were examined using 30, 0.6 × 0.9 m permanent quadrats photographed in 1959, 1964, 1968, 1978, and 2001 in Kosciuszko National Park, southeastern Australia. Cover attributes were assessed using a 130-point grid superimposed over each slide/photograph. For the 18 permanent quadrats near Mount Gungartan, where grazing ceased in 1958, there was a pattern of increasing vegetation cover. Bare areas were initially colonized by herbs, with native grasses, the lateral expansion of existing shrubs, and other herb species eventually replacing the colonizing herbs. For the 12 quadrats near Mount Kosciuszko, where grazing ceased 15 years before the survey, vegetation cover was high (around 94%) in all surveys except at the end of a long drought. The drought caused an increase in litter at both locations as graminoids died back. Graminoid cover recovered relatively rapidly and had reached pre-drought levels by 1978 and remained high. Herb cover was dynamic after the initial recovery from grazing, with a trend for reduced herb cover after 1964. The pattern of recovery from these two types of landscape level disturbances differed due to the different responses of the major life forms to bare ground, litter, and existing vegetation cover. The study also highlights the benefits of existing long-term monitoring programs.

We evaluated the importance of the northern pocket gopher (Thomomys talpoides) in controlling plant species composition and richness in two alpine tundra plant communities. We hypothesized that forb diversity and relative abundance is modified by gopher mounding activities in moist meadows of Niwot Ridge, Colorado, U.S.A., where both the pocket gopher and forbs are most concentrated. We tested this hypothesis with simulated gopher mounds. Forbs recovered faster following burial than graminoids or cushion plants, demonstrating a resilience that we propose confers a competitive advantage over other growth forms and favors forb dominance in moist meadows. Gopher effects on species richness varied according to spatial scale of measurement and community type. For one decade we monitored the responses of a sedge-dominated community to gopher activity in 1.5 m² plots that included both gopher mounds and intermound spaces and found that species richness was significantly positively correlated with recent disturbance. Species richness on the simulated gopher mounds (0.2 m²) immediately declined significantly after burial but recovered within a year. When evaluated in conjunction with studies of gopher diet preferences and effects on ecosystem biogeochemistry, our findings suggest that the northern pocket gopher is instrumental in constructing a locally diverse alpine plant community.

The Khangchendzonga Biosphere Reserve in the Sikkim State, India, with an area of 2620 km², forms an important reserve to protect biodiversity, habitats, and landscapes of the eastern Himalayan region. More than 18% of the area supports alpine vegetation, which is extensively used as summer grazing grounds by transhumance and nomadic graziers. Despite the global recognition of the region, unfortunately no report has so far been made available on the vegetation composition of the reserve. The present paper reports on floral diversity, economic use, and nutrient contents of selected alpine pastures at elevations between 3800 and 4800 m above sea level in the Khangchendzonga Biosphere Reserve. The growing season lasts from April to October, and during the rest of the months, the area remains under snow. The pastureland showed high species richness: as many as 202 plant species were present. These belong to 38 families, of which 90% of the species are dicotyledons and 9% are monocotyledons. Plant diversity and density increased from April until August and decreased thereafter. Monocotyledon species, such as Poa angustifolia, show high dominance during the early and late parts of the growing season, whereas dicot species proliferate mainly during the middle part of the growing season. Asteraceae, Ranunculaceae, Ericaceae, Primulaceae, and Rosaceae are dominant plant families in the area. Life-form distribution patterns showed that >50% of the species were chamaephytes, showing high adaptation by the plants. Besides using the area for grazing, the local people also collect various species for medicine, incense, tea-substitute, and aesthetic purposes. The belowground plant parts contributed nearly 90% of total plant biomass, whereas the aboveground biomass contributed just 10%. Such partitioning of biomass is considered beneficial in pastureland, as the belowground biomass helps the immediate recovery of vegetation after grazing as well as at the start of the growing season. Most of the species are highly nutritive and have high mineral contents, and animals showed a preference for species with low lignin content. In order for the area to continue to provide an important pasturage for animals in the future, the grazing pressure must not exceed an optimum level so that the high species diversity can be conserved.

We investigated the response of an alpine lichen heath plant community to an increase in soil nutrient and water availability. A 5-yr experiment—including additions of calcium, phosphorus, nitrogen, and nitrogen phosphorus as well as irrigation—was conducted in northwestern Caucasus, Russia, at 2800 m above sea level. Number of plants and generative shoots per species were counted annually. The plant-community composition started to change during the second year of treatments. Plant density and flowering of the community is co-limited by nitrogen and phosphorus. Irrigation and calcium additions caused minimal changes. The total number of forb plants per square meter was not influenced by treatments, whereas the total number of graminoid plants slightly increased in response to P treatment and strongly increased in response to N P treatment. Forbs responded to N and N P treatments by an increase in the number of generative shoots. Individual species differed in their response to treatments. Only clonal species responded to experimental treatments, except for one annual nonclonal species, which increased its abundance in response to irrigation. Biodiversity estimated by the Shannon-Wiener index decreased under N P treatment. Species number was not affected by any of the treatments.

Climate-driven northern limits of cold-hardy conifers, Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.), reach latitude 70°N in Fennoscandia. Spruce timberline is located at significantly lower latitudes than pine timberline, but factors contributing to this exceptional pattern have remained obscure. We assessed soil-water and soil-nutrient regimes across the spruce timberline in Finnish Lapland through the use of terrestrial electromagnetic (EM) measurements. These included soil dielectric permittivity (ϵ), which is positively correlated to soil-water content (θ_v); gamma radiation (γ), which is negatively correlated to soil-water content (θ_v); and electrical conductivity (σ_a), which is a measure of solute content of a soil. The soil EM data were acquired at 15 sites carrying mature (older than 150 yr) stands dominated by either spruce or pine; the sites fall along a 50-km-long transect that crosses the spruce timberline. The correlation and artificial neural network (ANN) analyses revealed that the soil-moisture and solute content were significantly higher in glacial tills of Norway spruce stands compared to those of stands formed by Scots pine. The stands dominated by spruce were associated with mesic-wet and nutrient-rich tills derived from mafic amphibole and hornblende gneisses of the Tanaelv Belt. Dry and nutrient-poor till derived from felsic garnet gneisses of the Lapland Granulite appeared to constitute an edaphic dispersal barrier for Norway spruce.

The effects of artificial warming on shoot elongation of alpine dwarf pine (Pinus pumila) was studied near Mount Shogigashira summit, central Japan, from 2001 to 2003. A nylon windshield net enclosed two experimental plots, 2 × 2 m, each year at the start of the growing season (June, but late July in 2001). The nets were removed at the end of the growing season (late September or early October). Two plots, 1.5 × 1.5 m, without a net were set as controls. In September 2001, the daily mean air temperature differed little between the experimental and control plots: compared to the control plot, the maximum was 4.3°C higher and the minimum was 1.7°C lower in the experimental plot. The annual shoot elongation differed little between the experimental and control plots in 2001 and 2002, but it was greater in the experimental than in the control plot in 2003. Shoot elongation started in June and ended in August in both experimental and control plots, but the rate of the increase was greater in the experimental than in the control plot in 2003, and so shoots had greater elongation in 2003 in the experimental plot. Thus, artificial warming promoted shoot elongation by increasing the daily maximum temperature.

A combination of empirical modeling and a diatom-based transfer function was developed to reconstruct air temperature and ice-cover duration through the study of lake sediments. By using a thermal degree-day modeling approach, ice-cover duration on European mountain and sub-Arctic lakes is found to be very sensitive to temperature change. For example, our model, which incorporates a weather generator, predicts a 100-day shortening in ice-cover duration for a 3°C temperature rise for catchments at elevations of 1500 m in the Southern Alps and the Pyrenees. For the more maritime lakes of Scotland, 30% higher sensitivities (130 d per 3°C) are found, whereas lakes in northwest Finland, in a more continental setting, have only half the sensitivity (50 d per 3°C). A pan-European data set of the species abundance of 252 diatom taxa in 459 mountain and sub-Arctic lakes has been compiled and taxonomically harmonized. Transfer functions were created that relate both seasonal air temperature and ice-cover duration to diatom species composition on the basis of a weighted averaging–partial least squares (WA-PLS) approach. Cross validation was used to test the transfer functions. For ice-cover duration the pan-European data set yields an R-squared value of 0.73, a jack-knifed R-squared value of 0.58, and a residual-mean-square error of prediction (RMSEP) of 23 days. A regional, northern Fennoscandian transect (151 lakes, 122 taxa) yields a jack-knifed R-squared value of 0.50 and an RMSEP of 9 days. For air temperature the pan-European database displayed greatest skill when reconstructing winter or spring temperatures. This result contrasts with the summer temperatures normally studied when using local elevation gradients. The northern Fennoscandian transect has a remarkably low winter RMSEP of 0.73°C.

Willows (Salix spp.) are important riparian plants along high elevation streams of western North America, but the hydrologic conditions needed for initial recruitment are not well defined. A replicated plot experiment was used to determine the effects of (1) elevation above the stream (high, middle, or low), (2) soil texture (sand or gravel), (3) watering to simulate additional rainfall, and (4) an upstream water diversion on soil water content and first-year willow seedling survival along a subalpine reach of the Colorado River.

Soil water content varied with elevation (F = 163.8, p < 0.001) and soil texture (F = 387.3, p < 0.001), while the effect of the watering treatment was not statistically significant. Soil water content controlled first-year willow seedling survival (r² = 0.257, p = 0.002), and no seedlings were found in plots with a mean soil water content of less than 15%. Sandy sites near the river elevation provide the optimal conditions for initial establishment of willows along this and other subalpine streams in the semiarid western United States. Potential establishment sites occur along abandoned channels and in drained beaver ponds, and creation of these sites depends on the occurrence of high flows. Therefore, as at lower elevation, cottonwood-dominated systems, maintenance of a flow regime that includes periodic high flows is essential for sustaining willow establishment along subalpine streams.

The upstream diversion reduced the stream stage by up to 13 cm during the growing season, resulting in a similar decline in the water table level and a reduction of up to 15% in plot soil water content. Since seedling survival depends on the availability of soil water, water diversions may adversely affect willow establishment along subalpine streams.