Since the 1970s, a breeding colony of lesser snow geese (Chen caerulescens caerulescens L.) at La Pérouse Bay, Manitoba, has grown 8% annually. This increase has led to significant loss of plant cover in all major salt- and freshwater coastal habitats between 1976 and 1997. A series of transects established in 1976 was resurveyed in 1997. Exposed sediment, extent and type of vegetative cover, and aquatic areas were recorded along transects using a classification of 12 a priori classes. Five regions within the colony were identified, and changes in vegetation cover differed among these and depended on unique combinations of vegetation class and year. Grubbing by geese has led to loss of graminoid plants, especially in intertidal and supratidal marshes. Exposed sediments have largely replaced previously vegetated areas since 1976. Species characteristic of disturbed sites have colonized exposed sediment with the most abundant species varying according to soil conditions. In intertidal marshes, willow cover declined in association with the development of hypersalinity after loss of the graminoid mat, but willow cover increased at the base of well-drained beach ridges and in a river delta with ample winter snow accumulation and freshwater flow in spring that protected ground vegetation. Most of the expected successional trends associated with isostatic uplift and changes in soil organic matter failed to occur because of intense goose foraging throughout the 20 years. The likelihood of sustained recovery of plant communities in the immediate coastal zone is very low, as long as goose numbers continue to increase. Indirect effects of vegetation loss (e.g., hypersalinity) and subsequent erosion of exposed sediments following grubbing will delay plant colonization and retard succession.

Systematic errors in precipitation measurements are known to affect all types of precipitation gages. These errors are more sensitive for solid precipitation than for rain. In arctic regions, these systematic errors become significantly more pronounced than for other regions due to the relatively slow precipitation rates, low temperatures, high winds, and low annual precipitation amounts that are characteristic of the arctic climate. This study performed the daily adjustments of measured precipitation data for the National Weather Service (NWS) stations at Barrow and Nome, Alaska, over a 7-year study period, from 1995 through 2001. The results of this study indicate that the bias adjustments increase the average monthly gage-measured precipitation by approximately 20%–180% for Barrow and 30%–380% for Nome, with the larger percentages occurring in winter months. The average gage-measured annual precipitation amounts are increased by approximately 70% for Barrow and 130% for Nome. It is expected that these increases will impact climate monitoring, the understanding of the arctic freshwater balance, and the assessment of atmospheric model performance in the Arctic.

Age structure, tree characteristics, and environmental data were used to analyze the status of the birch treeline in three regions along the Scandes Mountains from 62°10′N to 69°50′N. Aspect and estimated relative radiation explained most of the treeline altitude across studied regions, but not all variation. Main tree establishment occurred during the 1940s in the southern and northernmost regions, and during the 1960s in the middle region. Age distribution patterns at 2 m (tree size), however, showed stable or possibly progressive treelines in the southern and middle regions but recent recession in the north. Growth rates varied through time and between regions, with an apparent decrease in the north since the 1940s. Weak negative correlations between altitude and age in the south indicate recent changes favoring tree growth or increased turnover at higher, more exposed altitudes. Although Scandinavian treelines are expected to advance in response to climate warming, this was not evident as a general pattern for all regions. Seasonally different climate patterns, browsing, and abrasion are mechanisms involved in this. These regionally different patterns have to be taken into account in predictions of future responses to avoid overestimation of, e.g., ecosystem change, carbon uptake capacity, and feedbacks to climate systems.

Alnus viridis seedlings were planted on placer mine spoil in an Alaskan subalpine watershed to bypass a seedling establishment bottleneck for A. viridis, and to evaluate the interaction between A. viridis and the dominant riparian woody plants, Salix alaxensis and Populus balsamifera. The study area was divided into 11 replicate blocks, each on a homogeneous recontoured spoil pile. Blocks were divided into two 0.01 ha plots, and treatments without (control) and with 84 planted A. viridis seedlings were randomly assigned to plots. After 10 years, the Alnus treatment had a dense stand of A. viridis 1–2 m tall, while the control had fewer, smaller seedlings. Compared to the control, planted A. viridis had a neutral effect on S. alaxensis and inhibited P. balsamifera at the seedling establishment stage, but facilitated the growth of established plants of both species, with many plants overtopping the A. viridis canopy. Compared to the control, S. alaxensis plants in the Alnus treatment had higher levels of foliar N and δ¹⁵N values closer to those of A. viridis, indicating the importance of N fixation by A. viridis. Planting A. viridis accelerated the rate of succession by stimulating growth of woody dominants.

Streamflow, suspended sediment transport, and meteorological variables were measured during two field seasons in order to determine the climatic controls on daily discharge and suspended sediment load for three large middle arctic catchments. Substantive suspended sediment transfer only occurred during the short-lived nival peak, and the duration of the peak appears to be broadly scaled with interannual catchment snow water equivalence (SWE). Thermal energy was critical in generating streamflow and suspended sediment transfer, but only until watershed snowpack had been exhausted. Thus, total annual suspended sediment load in this environment is ultimately a function of total discharge through SWE rather than melt energy. Specific sediment yields were some of the lowest recorded in the arctic, ranging between 0.2 and 1.9 t km⁻²·a⁻¹. This study demonstrates the sensitivity middle arctic watersheds to both winter snowpack and spring thermal conditions and provides a basis for understanding the hydrological impact of future climate changes.

The City and Borough of Juneau, Alaska, has several major avalanche paths located in close proximity to population centers and is routinely affected by avalanche activity. As a result, developing a better understanding of the snowpack conditions that lead to avalanche cycles is of great interest. This study investigates temperature and vapor pressure gradients associated with near-surface faceted crystal formation in the high-latitude maritime snow climate of southeast Alaska. Here we report on two episodes in March and April 2003 in which temperature gradients measured in the upper 25 cm of the snowpack were in excess of 70°C m⁻¹. These temperature gradients were associated with strong near-surface vapor pressure gradients that exceeded 5 mb m⁻¹ for up to 48 h. During both episodes, faceted crystals 1–2 mm in diameter were observed to form near the surface of the snowpack. Field tests performed simultaneously at the study site demonstrated pronounced instabilities associated with the newly formed faceted crystals. Furthermore, avalanche activity was observed following both periods. Investigations of proximate avalanches showed that wind-loaded dry slabs were running on layers of near-surface faceted crystals.

Locally derived ice is often observed to fill through-cutting rifts and uneven fronts in ice shelves. That ice may nucleate as fast ice at the shelf front, by growth at the sea surface within rifts, or by basal accretion. Here, we investigate the role of such ice in the flow of the Brunt Ice Shelf and adjacent Stancomb-Wills ice tongue, along the Caird Coast of Antarctica. Much of the shelf system is severely rifted, with locally derived ice filling the space between rift walls and around ice rafts. A series of numerical experiments that account for thermal properties of the different ices is used to investigate the influence of that mixture of sea and marine ice on the kinematics and dynamics of the shelf system. The simulations are constrained by a variety of satellite remote-sensing data. We find that the locally derived ice forms a dynamic connection between the ice tongue and the Caird Coast, effectively creating an embayment where no coastal embayment exists. This may have implications for the expansion of ice shelves along arctic coasts during past glaciations.

We investigated biotic and abiotic associations for four growth forms in Chile's Parque Nacional Lauca, a tropical alpine puna ecosystem. We determined the biotic associations between Parastrephia lucida (Meyen) Cabr. [Asteraceae] and Festuca orthophylla Pilger. [Poaceae]. To determine if F. orthophylla was acting as a nurse plant for P. lucida, we used chi-square analysis to test for nurse plant effects. Our results indicated that F. orthophylla roots more often on bare ground and that P. lucida grows more often in association with F. orthophylla than would be expected. In testing for abiotic associations, we observed that both a tree, Polylepis tarapacana [Rosaceae], and a cactus, Tephrocactus ignescens [Cactaceae], showed positive abiotic associations with large boulders. These studies indicate that in an extreme environment, such as the South American puna, abiotic and biotic associations are important for plant survival.

We surveyed 14 ponds in 1999 and 28 ponds in 2000 to better understand the basic limnology of alpine ponds and to predict how the planktonic and epipelic (sediment-living) algal communities may respond to nutrient deposition and climate change. Based on nitrogen to phosphorus ratios, nitrogen limitation is likely common in these alpine ponds, which makes them particularly susceptible to current increases in atmospheric N deposition. Regression and redundancy analysis (RDA) showed phytoplankton abundance and community composition was best explained by total phosphorus (TP), pH, and conductivity. Epipelon abundance was best explained by nitrite plus nitrate and community composition was best explained by TP and dissolved organic carbon (DOC) in addition to nitrite plus nitrate. Some of these chemical variables, DOC, pH, and conductivity, have been linked to climate in alpine ponds and lakes and in low elevation lakes, which suggests alpine ponds may be sensitive to climate change. However, because we found interannual variability in the environmental-algal relationships, several years of study may be required in order to make realistic predictions on how algal communities will respond to increasing nutrient deposition and climate change.

Data mining—the discovery of previously unknown information from a large collection of individual data sources—is becoming increasingly popular for scientific data archives. We describe an approach to data mining that uses spatial, temporal, and type constraints to obtain a broad list of data that are potentially related to a data set of interest. Tree- and spline-based multivariate regression and classification techniques are then used to identify functional relationships between the data. Expert knowledge is used to constrain and guide the model building and evaluation process.

We demonstrate the approach by identifying relationships between indicators in a state of the Antarctic environment reporting database. Analyses of the fuel usage of electrical generators and boilers at Australia's Davis station yielded fuel usage dependencies on air temperature and wind speed that were in good accordance with known physical processes. The phenomenon of periodic haul-outs of large numbers of leopard seals on Macquarie Island was related to anomalies in regional sea ice cover and sea surface temperature.

An alpine fellfield community on granite substrate (elevation 3750 m) near the University of California Barcroft Laboratory in the White Mountains of eastern California was studied during the 2000 growing season to determine whether classic perennial life forms can be treated as plant functional groups. A series of 1-m² quadrat samples were measured to determine common species. The four species with greatest cover were Penstemon heterodoxus var. heterodoxus, Trifolium andersonii var. beatleyae, Poa glauca subsp. rupicola, and Eriogonum ovalifolium var. nivale. These and four additional common perennial species were selected for ecophysiological studies representing four distinct ecological life forms: chamaephytes, cushion plants (including mat formers), herbaceous dicot perennials, and graminoid perennials. Summer midday leaf temperatures for species with foliage held close to ground surface were up to 20°C higher than air temperatures, whereas on upright species, leaves away from the ground surface closely matched ambient temperatures. For the eight species, peak values of mean maximum photosynthetic rates ranged from 11.5–25.5 μmol CO₂ m⁻² s⁻¹, typical of published values, although chamaephytes in the study showed higher rates comparable to herbaceous perennials. Water-use efficiency, as estimated by a ratio of internal to ambient CO₂, was relatively high (c_i:c_a ratios of 0.43–0.59) compared to published data. During the stressful end of the growing season, neither predawn nor midday shoot water potentials ever reached low levels, presenting conflicting evidence for the role of soil moisture as a limiting factor. Overall, the data on plant functional attributes showed no strong patterns of differences between categories of life forms in the fellfield community, suggesting that classical life forms in this habitat do not represent plant functional groups.

Poa annua, the only alien plant species recorded on subantarctic Heard Island, considerably expanded its range and abundance along three transects in tundra-like vegetation on the island in the period 1987–2000. This expansion was strongly associated with increased seal disturbance, which also favored Callitriche antarctica and damaged Pringlea antiscorbutica, leading to a decrease in mean vegetation height. Expansions of Azorella selago and Poa cookii were independent of the expansion of P. annua, relating to colonization of moraines. There was no evidence of displacement of other taxa by Poa annua in areas undisturbed by seals.

The course of nitrogen fixation by moss-associated cyanobacteria in Svalbard (78°N, 16°E), Norway, was studied using the acetylene reduction assay. In situ field measurements of nitrogen fixation activity were conducted in six different types of moss-dominated arctic vegetation from the beginning of the snowmelt in early June to the end of July 1998. Concurrently, the water content of the soil/vegetation layer was determined and correlated with the nitrogen fixation rates. At all sites with diminishing water content during the summer season, nitrogen fixation activity was positively correlated with the amount of available water in the vegetation. At two sites, where water content of the vegetation was constantly higher than 80% (w/w) throughout the season, nitrogen fixation activity was correlated with temperature. Depending on the type of vegetation, nitrogen fixation became limited when the water status fell below a minimum threshold level. The most desiccation-tolerant vegetation for nitrogen fixation activity was the cryptobiotic crust, where nitrogen fixation decreased only after the water content of the soil/vegetation was less than 50% of the its fresh weight, while in the other types of vegetation nitrogen fixation stopped when water content was around 60%. The results from the present study confirm that, in arctic regions with low precipitation during the growing season, nitrogen fixation in different types of vegetation is mostly limited either to the period of snowmelt when water is sufficiently available, or to habitats that stay wet during summer.

Range limits of temperate high-altitude plants may be controlled by tradeoffs between physically severe but uncrowded conditions, versus mild but crowded conditions. Because up-slope migration of lowland species may accompany global warming and earlier snowmelt, I tested whether crowding by neighbors vs. timing of snowmelt limit Potentilla diversifolia to later-melting sites in the Rocky Mountains (U.S.A.). I transplanted individuals from two altitudes to experimental plots within and below the species' range limit, and experimentally altered snowmelt timing and the density of neighboring vegetation. In contrast to theoretical predictions for biotic control of lower range limits, higher temperatures and drier soils contributed to markedly reduced survivorship and reproduction below the native-range regardless of treatment. Neighbor removal only marginally increased performance both within and below the native-range, suggesting that interactions with neighboring vegetation are much less important for distribution than abiotic factors. Populations from the subalpine zone had longer growth intervals and grew larger than those from the alpine tundra in their native sites, but did not outperform alpine tundra populations when grown below the species' range. Although earlier snowmelt enhances growth, phenotypic plasticity may enable P. diversifolia to persist in later-melting tundra sites while higher temperatures and drought restrict it from much of the subalpine zone.

Three major rainfall events have caused considerable damage in the Valais region (Swiss Alps) since 1987. Substantial debris flows originating from periglacial environments were recorded during the August 1987 and September 1993 rainfall events, whereas no debris flows occurred in October 2000. This paper aims at putting these large-area events and the apparent increase in debris-flow frequency into a wider context by reconstructing the past debris-flow activity in the Ritigraben torrent (Mattertal, Valais) with dendrogeomorphological methods. Tree-ring analysis allowed the reconstruction of 53 events, going back to the year 1605. Previously, only 10 debris flows had been known for the torrent, and these were limited to the period between 1922 and 2002. Results further show that the apparently above-average concentration of events since 1987 was mainly caused by insufficient and short archival data. In fact, debris flows occurred even more frequently in the nineteenth century than they do today. The spatial distribution of injured trees in particular years further indicates that significant events, like the one in 1993, always occurred in the torrent. Finally, reconstructed event years were compared with archival data on flooding in neighboring catchments. The comparisons prove that large-area events like those in 1987, 1993, or 2000 have at least been as common in the past as they are today.

We investigated the influence of nitrogen (N) and phosphorus (P) on N₂-fixation and abundance of two of the most common N₂-fixing arctic lichens, Peltigera aphthosa and P. polydactyla, in two common moist upland tundra types, acidic and non-acidic tundra, at Toolik Lake, Alaska. Acidic tundra has higher N and lower P availability than non-acidic tundra. We measured the abundance of the lichens in control (no fertilization), N- and P-fertilized plots, and N₂-fixation using the acetylene reduction assay method on lichens from control and P-fertilized plots from both tundra types. Lichens on N-treated plots were too scarce to include in our N₂-fixation estimates. Lichen abundance was lower in plots fertilized with N than in control and P-fertilized plots, while per-biomass N₂-fixation rates were higher in P-fertilized plots than in control plots. Per-biomass rates of N₂-fixation did not differ between acidic and non-acidic tundra, but both lichen species are more abundant on acidic tundra. Thus, despite per-biomass stimulation of N₂-fixation by experimental P addition and reduction in lichen abundance with N fertilization, Peltigera contributes more N to the acidic tundra site, indicating that soil N and P availability are not the primary controls of N₂-fixation and abundance of these lichens.

The periglacial temperature regime in cool scree slopes located at subalpine altitudes of only 300–600 m a.s.l. in the Czech highlands is described and proved by the occurrence of a relict population of the predatory mite Rhagidia gelida Thorell (Acari, Prostigmata, Rhagidiidae). The mite has a circum-boreal pattern of distribution today, but its disjunct populations have an island-like pattern of distribution in the cool screes in the Czech highlands. R. gelida is univoltine, freezing intolerant, and considered a biological cryoindicator of the periglacial microclimate. As coolness is needed for R. gelida to survive in the cool screes, it is concluded that the scree slope patchy permafrost-like habitats have lasted continuously, perhaps persisting in modified form as paleorefugia, since the Pleistocene.