The effects of climatic conditions on the shoot elongation of alpine dwarf pine (Pinus pumila) were examined at its lower and upper altitudinal limits on Mt. Norikura (2500 and 2840 m a.s.l.) and Mt. Shogigashira (2640 and 2675 m a.s.l.) in central Japan. Altitudinal forest-structural changes were also described. Shoot elongation and stem height of P. pumila increased with decreasing altitude, but its abundance was markedly decreased at the altitudinal ecotone between the upper P. pumila zone and the lower Betula ermanii zone because of the suppression by tall B. ermanii. Thus, the lower altitudinal limit of P. pumila was probably determined by the competition with B. ermanii. The interannual variation in the shoot elongation of P. pumila was related to climatic conditions; long shoot length was associated with high summer temperatures of the previous year at both the upper and lower altitudinal limits on the two mountains. In addition, rates of the increase of shoot elongation in response to the increase of air temperature were not different between the upper and lower altitudinal limits. Thus, the increase of summer temperatures would enhance the growth of P. pumila from its upper to lower altitudinal limits. However, it is harder to predict the altitudinal distribution shift of P. pumila due to environmental change because its lower altitudinal limit is largely affected by competition with B. ermanii. Therefore, this study concluded that long-term monitoring of the population dynamics at the P. pumila–B. ermanii ecotone is necessary to predict the distribution shift of P. pumila.

Gradients of humidity on tropical high mountains are reflected by shifts of vegetation belts and changes in species composition and vegetation structure on the wind- and leeward sides. The superpáramo flora and vegetation were studied on opposite sides (west and east) of two Ecuadorian mountains, Chimborazo and Antisana. Zonal vegetation was studied in vegetation samples set out in a semirandom way, and the data were complemented by species occurring in azonal habitats. Ordination and clustering techniques were used to analyze the vegetation samples, while two different measures of the floristic similarity (index of quantitative floristic similarity and comparison of the observed and expected numbers of species shared between the mountain pairs) were employed to evaluate the floristic relationships between the study sites. The superpáramo belt occurs asymmetrically, with regard to altitude, on the two mountains, being generally lower on the eastern side. Slopes with corresponding aspects between the mountains were more similar than were the opposite slopes of each mountain. The observed floristic pattern is interpreted in the context of the precipitation gradient leading to a rain-shadow on the western side of the mountains. The occurrence of the desert-like area, the so-called Arenal Grande, and the unique páramo vegetation on the western side of Chimborazo is discussed.

In alpine lakes from several regions of the world, sedimentary diatom profiles indicate that rapid shifts in diatom community structure have occurred over the past century. A number of these recent shifts have been attributed to anthropogenic disturbances such as enhanced atmospheric nitrogen (N) deposition or climate change. When these disturbances are coupled, the response of alpine lakes becomes more complex and varies from region to region. The Beartooth Mountain Range, situated on the border between Montana and Wyoming, is part of the central Rocky Mountains; it is considered an area of relatively low N deposition but has experienced an increase in bulk precipitation rates, primarily in the form of snowfall, over the past century. We have examined a 400-yr sediment record from Beartooth Lake and have observed a rapid change in the diatom community structure over the past decade. A typical alpine lake diatom flora, consisting mainly of small Fragilaria sensu lato species, dominated this lake until approximately 1995, at which time Fragilaria crotonensis and Cyclotella bodanica var. lemanica rapidly increased to approximately 30% each of the total assemblage. The diatom assemblages from the tops and bottoms of short cores from three additional lakes in the area also reveal taxonomic shifts. These shifts appear indicative of both increased N loading to these systems as well as changes in thermal stratification patterns.

Three arrays, each containing four funnel-shaped sediment traps, were deployed near the front of the Müller Ice Shelf, Lallemand Fjord, western Antarctic Peninsula, in late austral summer 1998. Although the upper traps in each array were damaged or lost, eight others were recovered intact about 13 mo later. The mean flux of sediment was 1.4 to 2.9 mm a⁻¹ (1.67 to 3.5 kg m⁻² a⁻¹) and showed little trend with respect to distance from the ice shelf or depth of water. Mean organic carbon and biogenic silica concentrations are 0.6 to 1.1% and 3.4 to 5.0%, respectively. Up to 50 microlaminae visible in x-radiographs probably indicate storm surges or the effect of spring tidal cycles. The sand content in most traps is 2 to 5 times lower in winter, reflecting reduced melt from icebergs and their limited mobility as they are held by sea ice. However, a secondary winter peak in very coarse sand is probably associated with eolian input during winter storms. Nitrogen is greater by 2 to 3 times in summer sediment, and organic carbon is up to 4 times greater. Biogenic silica shows less summer to winter difference, although the spring diatom bloom is represented by somewhat greater values in most traps. Summer values of isotopic organic carbon δ¹³C and total nitrogen δ¹⁵N are lower than winter values in response to heterotrophic removal of the lighter isotopes.

Soil microbial properties were investigated to assess the potential of organic matter dynamics in mineral and ornithogenic soils in a cold climate. Microbial biomass, respiration, N-mineralization, and enzyme activities were measured along two catenary transects crossing penguin rookeries and seabird colonies. Ornithogenic excrements, total organic carbon (TOC), and phosphorus accumulation were major factors controlling microbial properties in Antarctic soils. Multivariate approaches (cluster and discriminant analysis) clearly distinguished the ornithogenic soils from the mineral soils based on their microbial characteristics. Microbial biomass, respiration, and N-mineralization were gradually inhibited by increasing P-inputs by penguins. The metabolic quotient (qCO₂) was negatively correlated to P-content, whereas all other microbial properties (microbial biomass, respiration, N-mineralization, enzyme activities) followed the patterns of TOC. Urease, xylanase, phosphatase, and arylsulfatase activities were significantly favored by penguin and seabird excrements in the ornithogenic soils compared to the mineral soils. Microbial biomass-to-enzyme activity ratios were substantially higher at sites influenced by penguin guano than by other seabird excrement. We show that enzymes are active in antarctic soils, and that high levels of biomass-based specific activity in the ornithogenic soils, compared to those of mineral soils, result from continuous input of large quantities of enzyme-rich penguin guano.

Subalpine grasslands in the western Alps are currently facing major environmental changes induced by pastoral disuse. In such a context, the rapid spread of a shrub (Alnus viridis [Chaix] DC.) is expected to threaten biodiversity. The aim of this study was to assess the impact of its cover on vascular plant diversity. Data collected at several local levels (108 plots) in a representative area detected a linear decrease in species richness across an increasing A. viridis (green alder) cover gradient, whereas alder-stand β-diversity at the community level was particularly singular. We used constrained ordination methods based on Principal Components Analysis to partial out substantial variance explained by spatial structure of samples. The resulting partial Redundancy Analysis accounted for 62.3% of the initial inertia, and the environmental effect by A. viridis cover was identified as a major cause of variance in the whole species ordination (16.1%). The expansion of A. viridis on subalpine grasslands causes considerable environmental changes which have mostly a negative effect on the conservation of vascular plant diversity in the inner part of the western Alps. However, A. viridis appears to contribute to the diversity of the subalpine belt by inducing a peculiar floristic composition.

This article presents paleobotanical and paleoclimatic reconstructions of the New Siberian Islands for the past 15,000 years based on data from Quaternary geology and archaeology collected in the late 1980s and early 1990s as part of research conducted by the Arctic and Antarctic Research Institute, St. Petersburg, Russia. The data were obtained from 18 reference sites from Holocene and upper Pleistocene deposits on Kotelny Island, the largest island of the New Siberian Archipelago, and from the smaller and more northerly Zhokhov Island. Conclusions are also drawn from the composition of the avian fauna recovered during the excavations of the Zhokhov archaeological site on that island. The composition of bird species is an important source of information which helps interpret the results of palynological analysis because the birds are very sensitive indicators of changes in temperature and vegetation. The palynological analysis has revealed a sequence of 13 spore-pollen complexes that have been generalized as a scheme showing a broad sequence of events in the area of survey. The complexes belonging to the early Holocene time are markedly different from the others. The most favorable conditions occurred in the time span from 10,000 to 9000 BP. After 8000 yr ago the fluctuations were of lesser amplitude, and both their sequence and timing were close to those of Northern Europe, though there appear to be differences between the two areas in the range of variation.

The late Holocene history of eolian activity in a parabolic dune complex in the northern Chugach Mountains, Alaska, is reconstructed using 80 tree-ring dates and 5 radiocarbon ages. A radiocarbon age on detrital organics shows mobilization of sands about cal yr A.D. 1260. General forest growth over the dune field area indicates that this active interval was followed by dune stabilization by A.D. 1500. The present interval of dune migration activity, reconstructed from calendar dates and radiocarbon ages on buried trees, began as early as the late A.D. 1600s, was well under way by the mid–A.D. 1700s, and continues today at a diminishing rate. Intervals of increased eolian activity correspond with pulses of the Little Ice Age as reconstructed from a well-established glacial history for the region over the last 1000 yr. Century-scale cooling in climate appears to have forced dune activity through general geomorphic instabilities of nearby glacial and fluvial-lacustrine systems. Geomorphic activity includes a combination of dynamic fluvial incision of cutbanks and release of dormant dune sands, increased wind intensity, as well as internal feedback mechanisms associated with parabolic and blowout dune dynamics. Over the past 200 yr, average rates of dune migration between 1 to 3 m yr⁻¹ are estimated using tree-ring dating. Observations and tree ages along the dune margins suggest that vegetative cover may now be increasing and dune stabilization may be under way.

We divide the Alaskan Arctic cold season into five stages based on transitions in climatological and thermophysical conditions in the atmosphere, snowpack, and soil active layer. Each of these stages has distinct characteristics which drive ecosystem processes. During the two autumnal stages (Early Snow and Early Cold) soils remain warm, unfrozen water is present, and the highest rates of cold-season soil respiration occur. The next two stages (Deep Cold and Late Cold) are characterized by a frozen active layer with decreasing temperature. Thaw is critical in determining the length of the growing season and the resumption of biological processes. Deep Cold and Late Cold result from a radiation deficit, show little interannual variation, and will be resistant to change under almost any reasonable climate change scenario. These are also the stages with the least amount of biological activity and have the least impact on the ecosystem. However, Early Snow, Early Cold and Thaw stages vary significantly from year to year, have more ecosystem implications, and are also the most likely to undergo significant change in timing and character as the arctic climate changes. This 5-fold subdivision is useful for framing discussions of biophysical interactions during the arctic winter and for focusing attention on critical cold-season periods.

This paper contains an analysis of magnitude and frequency of avalanches in relation to terrain and forest cover variables. The analysis was applied to 194 avalanche paths in four avalanche areas along highways in British Columbia with approximately 25,000 avalanches recorded. The magnitude and frequency for the avalanche paths were estimated from data collected along the highways by avalanche technicians. Results show that mean magnitude and mean frequency are weakly correlated for a set of avalanche paths in an avalanche area. In addition, with magnitude and frequency viewed as response variables, magnitude and frequency correlate with different sets of predictor variables from one area to another. This paper contains the first comparison of variables which correlate with magnitude and frequency from one avalanche area to another. The results show that previous studies conducted for single areas are simplistic. However, there is some consistency between areas. Avalanche frequency is most directly related to terrain steepness and snow supply. Average avalanche magnitude appears related to terrain steepness, starting zone, and track confinement and the scale (e.g., total vertical drop of the path) with only indirect evidence for a link to snow supply.

The McMurdo Dry Valleys is the largest of the ice-free areas in Antarctica. Precipitation events in excess of 1 cm of snow accumulation are rare. During the winter, snow is transported by strong katabatic winds blowing from the polar plateau, and deposited into the lee of topographic features (e.g., stream channels and other topographic depressions). At the start of the austral summer (early October), as much as 10% of the valley soils may be covered by distributed snow patches. Because liquid water is the primary driver of biological, physical, and chemical processes in this polar desert, quantifying fluxes of water from snow patches is important to understanding the influence of hydrology on soil biology and nutrient cycling. During the austral summer of 1999–2000, four snow patches that had developed during the previous winter in Taylor Valley were studied. We measured snow-patch area, depth, and snow water equivalent, as well as subnivian (under snow) and nearby exposed (control) soil temperature, light intensity, soil moisture, invertebrate abundance, soil organic matter content, and 95-d labile pools of C and N. Subnivian soils differed from exposed soils being as much as 26.8°C colder than exposed soils; average soil moisture ranging from 6.9 to 13.6% compared to 0.4% in exposed soils; soil invertebrate populations exceeding 7900 individuals kg⁻¹ dry soil versus less than 1200 individuals kg⁻¹ dry soil in exposed soils; and soil invertebrate species richness values greater than 2 taxa, compared to 1.3 taxa in exposed soils. The results of this study show that these seasonal, sparse snow patches may be an important source of moisture and control habitat of soil ecosystems in this extreme environment.

Microtus richardsoni, the water vole, was listed as a sensitive species in Region 2 of the USDA Forest Service in 1994. Historical records indicate water voles were found in the Big Horn Mountains, but little was known about their current status. The purpose of this study was to locate water voles in the Big Horn Mountains of Wyoming, develop a habitat profile, and evaluate the extent to which livestock grazing affects them. Accessible creeks with habitat requirements for water voles were surveyed. Water voles were not captured below 2440 m. Grazed and ungrazed sites occupied by water voles were matched and analyzed for percent plant cover, dry weight biomass, riparian classification, mean stream depth, channel type, elevation, precipitation, and temperature. Capture success was significantly greater in ungrazed areas. Percent cover by ferns and thallophytes was significantly greater in areas where water voles were more abundant, and bare ground was significantly greater at grazed locations. Water voles were most abundant on Rosgen B or E streams with a willow/wet Carex riparian class that is found on relatively undisturbed sites with stable, well-developed soils and bank structure. In the Big Horn Mountains, water vole captures were low in comparison to the Beartooth Mountains and synergistic effects of grazing and drying might negatively impact this species.

Changes in diatom assemblage composition since preindustrial times were analyzed in a landscape paleolimnological study of 50 lakes and also in a more detailed analysis of a dated sediment core from Slipper Lake in the Canadian central arctic treeline region. The most apparent taxonomic shift was toward a higher relative abundance of the planktonic Cyclotella stelligera complex and a lower relative abundance of benthic Fragilaria taxa (F. pinnata, F. construens var. venter, F. construens, and F. brevistriata) in the modern versus the older sediments. Diatom assemblage composition in Slipper Lake recorded a marked change in the top 5.0 cm (ca. mid-1800s) of the core with a clear shift to a more planktonic diatom assemblage characterized by higher percentages of the Cyclotella stelligera complex. Possible causative factors, such as recent anthropogenic acidification, nutrient enrichment, or atmospheric deposition of contaminants, do not appear sufficient to explain these species changes. Instead, these recent assemblage shifts are consistent with limnological changes occurring with climatic warming, such as a shorter duration of ice cover, a longer growing season, and/or stronger thermal stratification patterns.