A method for long-term simulation of snow avalanches is developed, based on coupling statistical interpretation of triggering snowfall process and regional avalanche data. The case study area is the Alta Valtellina region, in the northern Italian Alps. Therein, a 21-year-long series of daily snowfall data from 21 snow stations is used to calibrate a daily point snowfall statistical model. Then, a data set including 68 avalanche events from six historical avalanche sites are used to evaluate regionally valid features of avalanche release probability, geometry, and runout. These findings are then used to set up a model for the occurrence of avalanches. One particular case study site is considered, the Vallecetta mountain, of interest because of the considerable number of avalanche events occurring there. Long-term simulation of daily snowfall is performed, which is then fed into a model of snow avalanche occurrence. Snow avalanche simulations are then carried out, resulting in synthetic statistics of avalanche geometry, volume, and runout for a return period of 300 years. These are compared with regionally observed statistics in the considered area, resulting in acceptable agreement. The proposed model allows long-term simulations of avalanche occurrences for evaluation of snow avalanche volume and runout, usable for ecological and geomorphologic purposes. Integration with an avalanche dynamics model would provide long-term avalanche hazard assessment for land use planning purposes.

Plant species' requirements at seed and seedling stages are critical in determining their distributions. Proximity to adult plants, as well as the presence of litter or rocks on the soil surface can influence seedling success. By comparing the microsite characteristics of points occupied by naturally occurring seedlings to the characteristics of unoccupied points in fellfield and dry, moist, and wet meadow alpine plant communities on Niwot Ridge, Colorado, U.S.A., this study addresses the following questions: Are seedlings more likely to be near an adult plant or in litter than are unoccupied points? Does the proximity of seedlings to adult plants vary among communities? In the fellfield community, are seedlings more likely to be located next to a rock than are unoccupied points? I found that seedlings were farther from adult plants than were unoccupied points in the wet meadow, a community with dense vegetation cover and wet soils. Contrary to expectation, I also found that seedlings were farther from adult plants than were unoccupied points in the fellfield, the driest, most barren community. Seedlings were not more likely than unoccupied points to be located in areas of litter buildup, and fellfield seedlings did not occur disproportionately within the protection of a rock. This study suggests that competition between adult plants and seedlings may be taking place both in highly productive and in very unproductive alpine plant communities.

In 2007, the Anaktuvuk River Fire (ARF) became the largest recorded tundra fire on the North Slope of Alaska. The ARF burned for nearly three months, consuming more than 100,000 ha. At its peak in early September, the ARF burned at a rate of 7000 ha d⁻¹. The conditions potentially responsible for this large tundra fire include modeled record high summer temperature and record low summer precipitation, a late-season high-pressure system located over the Beaufort Sea, extremely dry soil conditions throughout the summer, and sustained southerly winds during the period of vegetation senescence. Burn severity mapping revealed that more than 80% of the ARF burned at moderate to extreme severity, while the nearby Kuparuk River Fire remained small and burned at predominantly (80%) low severity. While this study provides information that may aid in the prediction of future large tundra fires in northern Alaska, the fact that three other tundra fires that occurred in 2007 combined to burn less than 1000 ha suggests site specific complexities associated with tundra fires on the North Slope, which may hamper the development of tundra fire forecasting models.

Photosynthesis, as the basis of most food chains and a crucial global carbon sink, makes chief contributions to overall ecosystem carbon budgets, but specific responses of the plant component cannot be obtained from such budgets. To gain much-needed further information on possible interspecies differences in seasonal patterns of photosynthesis, capacities for light- and CO₂-saturated rates of oxygen evolution at 25°C (photosynthetic capacity) were determined during the summer-fall-winter transition for five conifer species over their natural distribution along a steep altitudinal gradient. Findings include (i) a transient upregulation of photosynthetic capacity during the summer-to-fall transition in all five conifer species that preceded the previously reported winter downregulation in conifers. However, there were (ii) interspecific differences in this response at the highest altitudes, with higher maximal photosynthetic capacities displayed by pine and spruce species compared to fir species. Lastly, the winter downregulation of photosynthetic capacity was not as complete in the present study (winter of 2006) as that which has been reported for previous winter seasons, which has implications for the winter survival strategy of conifers in response to global warming.

Snowpack evolution and glacier ice surface temperatures were studied on the Indren glacier (Northwestern Alps, Italy) under different meteorological conditions: in winter 2002–2003, rich in snow from the beginning of the season, and in winter 2005–2006, poor in snow until February. Periodical snow profiles were made to measure the physical properties of snow, while data loggers measured the snow/ice interface temperature. Furthermore, in winter 2002–2003, the influence on the snowpack evolution of an artificial increase in the snow density was evaluated.

During the season rich in snow there was a prevalence of rounded crystals originated by melt-freeze metamorphism, while in the season poor in snow depth hoar and faceted crystals prevailed, due to the higher temperature gradient.

From these two winter seasons, it appeared that a deep snow cover of at least 100 cm was able to maintain the snow/ice temperature at around −5°C until the snow cover reached isothermal conditions, whereas, during the winter of 2005–2006, the shallow depth of snow did not allow basal temperature to reach an equilibrium value and the snow/ice interface temperature oscillated between −2 and −8°C. The altered snow density had no effect on the snow/ice interface temperature, whereas it caused a delay in the time of reaching isothermal conditions, thus allowing snow cover on the glacier to persist longer.

An experiment was conducted in arctic tundra to evaluate the role of reindeer grazing, trampling, and feces and urine deposition in nutrient turnover and primary production. Grazing was simulated by mowing, trampling by the impact of a wooden pole, and waste product deposition by the application of fertilizer. In the first year, aboveground primary production increased with simulated grazing in the fertilized plots and decreased with simulated grazing in the unfertilized plots; this indicates a higher regrowth capacity at higher nutrient levels. However, nitrogen mineralization and primary production were mainly determined by the input or removal of nutrients and, therefore, decreased in plots that were grazed but not fertilized and increased in plots that were fertilized but not grazed. Simulated trampling decreased the depth of the moss layer and increased soil temperatures, but the higher temperatures increased N mineralization only in unmowed plots, and the increased nitrogen availability was not translated into increased primary production. Since aboveground and belowground net primary production in plots with simulated grazing was the same as in plots without simulated animal activity, this study indicates that an entire trophic level can be supported with no apparent effect on primary production.

This study examined levels of predation (% flower heads with insects and/or damage) and number of Tephritidae (seed-fly) in flower heads of 29 species of Australian alpine Asteraceae. Pre-dispersal seed predation was common among the Asteraceae, with all but four species with some flower heads containing Tephritidae. Levels of predation within species were also high, with most flower heads damaged in just under half of the species, and >90% of flower heads damaged in five species. Three species had flower heads containing Tephritis bushi (Diptera: Tephritidae, sp. nov.) while 23 species had flower heads containing Tephritis poenia (Diptera: Tephritidae (Walter)). Among species levels of all predation and number of Tephritidae per flower head were positively correlated with the diameter of the flower head, but not the color or type of flower head. The expected positive association between pre-dispersal seed predation and altitude and the negative association between predation and flowering time were uncommon among populations of 10 species tested. These results indicate that pre-dispersal seed predation is likely to be an important factor in the reproductive ecology of alpine Asteraceae, with species with larger diameter flower heads having higher levels of predation and more Tephritidae per flower head.

Indirect topographic variables have been used successfully as surrogates for disturbance processes in plant species distribution models (SDM) in mountain environments. However, no SDM studies have directly tested the performance of disturbance variables.

In this study, we developed two disturbance variables: a geomorphic index (GEO) and an index of snow redistribution by wind (SNOW). These were developed in order to assess how they improved both the fit and predictive power of presence-absence SDM based on commonly used topoclimatic (TC) variables for 91 plants in the Western Swiss Alps. The individual contribution of the disturbance variables was compared to TC variables. Maps of models were prepared to spatially test the effect of disturbance variables.

On average, disturbance variables significantly improved the fit but not the predictive power of the TC models and their individual contribution was weak (5.6% for GEO and 3.3% for SNOW). However their maximum individual contribution was important (24.7% and 20.7%). Finally, maps including disturbance variables (i) were significantly divergent from TC models in terms of predicted suitable surfaces and connectivity between potential habitats, and (ii) were interpreted as more ecologically relevant.

Disturbance variables did not improve the transferability of models at the local scale in a complex mountain system, and the performance and contribution of these variables were highly species-specific. However, improved spatial projections and change in connectivity are important issues when preparing projections under climate change because the future range size of the species will determine the sensitivity to changing conditions.

Mount Washington, New Hampshire, has the longest northeastern U.S. mountain climatological record (1930s to present), both at the summit (1914 m) and at Pinkham Notch (612 m). Pinkham's homogenized daily temperature exhibits annual (mean  =  0.07°C/decade, p  =  0.07; min  =  0.11°C/decade, p  =  0.01), winter (min  =  0.18°C/decade, p  =  0.07), spring (max  =  0.13°C/decade, p  =  0.10), and summer (min  =  0.11°C/decade, p  =  0.01) warming trends. Though suggesting annual, winter, and spring warming (0.05 to 0.12°C/decade), mean summit temperature trends were not significant. Pinkham shows no significant change in date of first and last snow; however, the summit does but its period of record is shorter. Onset of continuous snow cover has not changed significantly at either site. Thawing degree days trended earlier at the summit (2.8 days/decade; p  =  0.01) and Pinkham Notch (1.6 days/decade, p < 0.01), but end of continuous snow cover trended significantly earlier (1.6 days/decade; p  =  0.02) only at Pinkham. Growing degree days showed no significant trends at either location. Pinkham exhibits more climatic change than the summit but less than regional lower elevations. Thermal inversions and high incidence of cloud fog commonly at or above the regional atmospheric boundary layer may explain the summit's resistance to climate warming. Caution is needed when extrapolating climate change trends from other mountains or proximate lower elevation climate data to upper elevations.

Snowmelt timing is a critical factor for tree growth in high latitudes, but threshold conditions with respect to soil moisture availability and soil temperature for the root-zone processes are not well known. We monitored snowpack thickness, air and soil temperature, and water content in the soil, sapwood, and roots of downy birch (Betula pubescens Roth.) in Finnish Lapland through 1999–2003. An extreme cold event in January 1999 (T_AIR  =  −49°C) resulted in soil freezing (at 10-cm depth) down to T₁₀  =  −26°C at a snow-free site, but beneath the 50-cm-thick snowpack the soil temperature was T₁₀  =  −0.5°C. Snowmelt water was able to infiltrate partially frozen soil sequences, such that an increase in water content of the soil and birch roots occurred two to six weeks before soil temperatures rose notably above 0°C. The soil T₁₀ reached 0°C a week after the disappearance of snow. The increase in water content of birch trunks was coincidental with the air temperature rises notably above 0°C. The systematic interseasonal pattern of water content in the birch root-trunk system, i.e. high peaks in late winter–early spring and fall, suggests sap flow in downy birch.

During the early life-history stages, plants are especially susceptible to the abiotic conditions present in high mountain environments. At high altitudes, facilitative interactions between close neighboring plants may buffer seedlings from these abiotic pressures by providing shelter from frosts and winds. At lower altitudes, seedlings may not be so limited by the abiotic environment, and may therefore compete for resources with close neighboring plants. Using four alpine sites at different elevations (representing an abiotic stress gradient), we investigated how the presence of close neighboring plants influences seedling growth in their first growing season. We experimentally cleared above-ground vegetation and transplanted seedlings of three species into cleared and control plots. We quantified the stress gradient of abiotic conditions across sites by measuring ambient and soil temperatures, soil moisture, and soil frost heave. We used the “Relative Neighbor Effect” index to show the direction of the interaction between transplanted seedlings and their close neighboring plants. Aciphylla glacialis seedlings showed neutral interactions across the gradient of alpine sites, with undetectable change across the growing season, compared with Brachyscome rigidula seedlings which showed positive interactions with neighbors across the growing season at most sites. Trisetum spicatum seedlings showed mostly neutral interactions with neighbors at the higher elevations, and often negative interactions at the lower elevations, particularly midway through the growing season. Our findings highlight the importance of spatial and temporal plant-plant interactions with regard to seedling performance across altitudinal stress gradients.

The timing of germination is a critical life-history trait for annual plants because it coordinates development from seedling to reproduction with the growing season. Arctic/alpine annuals are subject to the constraints of an especially brief growing season in which temperature both acts as a germination cue and limits growth. The evolution of phenotypic plasticity in response to temperature is thus expected, measured as norms of reaction. Strong selection in combination with differences among habitats in appropriate temperature cues leads to the expectation of population divergence in norms of reaction. Their form may be complex; no a priori mathematical distribution can be assumed. Here, we use nonparametric smoothing (Loess) to detail norms of reaction of germination to temperature, and find significant genetic divergence among six widely distributed arctic and alpine populations of the annual Koenigia islandica from Norway, the U.S.A., and Canada. Germination plasticity is discussed in relation to temperature regimes recorded under field conditions; however, any adaptive inference based on lab observations must be interpreted cautiously. The present results indicate strong population differentiation in plasticity, and highlight the necessity to consider evolved differences in life-history traits when evaluating the vulnerability of arctic and alpine species to a changing climate.

The land-atmosphere interaction processes are unique at Mt. Everest as a result of high elevation. Based on turbulent data collected from April 2005 to March 2006 with the eddy covariance method at Quzong in the Rongbu Valley on the northern slope of Mt. Everest, land-atmosphere energy budget before and after the southwest monsoon onset and surface layer turbulent characteristics are studied for the first time. It is found that energy budget components (net radiation flux, sensible heat flux, latent heat flux, and soil heat flux) and surface heating field have strong diurnal and seasonal variations. In particular, under the influence of the southwest monsoon, the characteristics of surface parameters can be clearly identified. From pre-monsoon to monsoon season, the sensible heat flux decreases whereas the latent heat flux increases. The latent heat flux and Evaporative Fraction at Quzong are relatively high most of the year. Furthermore, the intensity of heating source in the wet season (from June to August) is much greater than that in the dry season (from October to December). The relationship between normalized standard deviation of wind speed and atmospheric stability, variations of normalized standard deviation of temperature, and humidity with atmospheric stability are analyzed using the Monin-Obukhov similarity theory. The result reveals that the normalized standard deviation of velocity components of the three-dimensional wind speed follows similarity relationships in the convective and near-neutral surface layer, but does not seem to be valid in stable surface layer. However, the normalized standard deviation of temperature and humidity does not obey Monin-Obukhov similarity theory in the entire interval of atmospheric stratifications.