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The treeline ecotone in northern Finnish Lapland is characterized by a mosaic of sites with highly varying environmental conditions. Density, age structure, growth, and root systems of mountain birch seedlings (Betula pubescens ssp. czerepanovii [Orlova] Hämet-Ahti) were studied in different microsite classes (deflation, lichen heath, dwarf shrub heath, hummock, willow shrub, sedge mire). On wind-exposed convex topography characterized by shortage of moisture and nutrients, seedling establishment is impeded, as is indicated by low seedling densities and lack of very young seedlings as well as by high rooting depths and root/shoot ratios of the few individuals. In sedge mires, birch seedlings occasionally occur in great numbers but die off at an early stage. Extremely shallow root systems point to anoxia as the main reason. Severe shoot damage is common to almost all saplings. This is likely due to grazing by reindeer (Rangifer t. tarandus). As a result, height growth is suppressed even on sites with otherwise relatively suitable conditions (e.g. willow shrub sites). Future effects of climate change which could locally improve conditions for germination and establishment of birch young growth might be overridden by the effects of high reindeer density.
Disturbance is likely to affect multiple life stages and may be most critical in seedling germination and establishment through indirectly affecting soil properties. Following disturbance, plants establish from seeds that either exist on the site or that disperse onto the site. Here, we examined the effects of a 1-year-old severe human disturbance (approx. 1 ha) on alpine vegetation recovery in the Andes of central Chile (33°S, 60°W) at 2800 m a.s.l. during two growing seasons (2006–2007). Particularly, we assessed the effects of soil properties and seed rain on post-disturbance seedling emergence using two sets of denuded slopes of different exposure (south and northwest, respectively) and two appropriate control areas. The disturbed area on the south-facing slope was drier than its respective control, while the opposite was observed on the disturbed area on the northwest-facing slope. The differences in soil water content between both slopes coincided with the results of seedling recruiting. The south-facing slope, with a more humid undisturbed area, showed a greater number of emerging seedlings than the disturbed slope. Conversely, on the northwest-facing slope, the main recruiting of seedlings was observed on the disturbed area, while the undisturbed area showed practically no emergence of new individuals. In addition, our results indicate that seedling recruitment occurred from a persistent seed bank constituted mostly by species with long-lived and deeply viable seeds, though in this particular study, we could not corroborate it empirically. Although long-term studies are desirable to make more definitive conclusions, our results provide the first step to understanding the capacity for vegetation recovery after a severe human disturbance in the Andes of central Chile, where seed banks and soil moisture seem to play a pivotal role.
The formation of many arctic wetlands is associated with the occurrence of polygon-patterned permafrost. Existing scenarios to describe and explain surface landforms in arctic wetlands (low-center and high-center polygons and polygon ponds) invoke competing hypotheses: a cyclic succession (the thaw-lake hypothesis) or a linear succession (terrestrialization). Both hypotheses infer the predictable development of polygon-patterned wetlands over millennia. However, very few studies have applied paleoecological techniques to reconstruct long-term succession in tundra wetlands and thereby test the validity of existing hypotheses. This paper uses the paleoecological record of diatoms to investigate long-term development of individual polygons in a High Arctic wetland. Two landform processes were examined: (1) the millennial-scale development of a polygon-pond, and (2) the transition from low-center to erosive high-center polygons. Diatom assemblages were quantified from habitats associated with contrasting landforms in the present-day landscape, and used as an analog to reconstruct past transitions between polygon types. On the basis of this evidence, the paleoecological record does not support either of the existing models describing the predictable succession of polygon landforms in an arctic wetland. Our results indicate a need for greater paleoecological understanding, in combination with in situ observations in present-day geomorphology, in order to identify patterns of polygon wetland development and elucidate the long-term drivers of these landform transitions.
Flight of alpine stream insects has not been well studied but is an important ecological process that ensures successful mating and allows gene flow among relatively isolated populations. In this study, we collected actively flying insects along a perpendicular transect from an alpine headwater stream in the Colorado Rocky Mountains (U.S.A.) during the summer emergence season in two consecutive years with contrasting hydrology: 2002 had minimal snowfall the previous winter, while 2003 snowfall was above average. Flight activity patterns among four common stream taxa were similar to previously reported results from streams below treeline: Ephemeroptera and Plecoptera declined as an inverse power function, Trichoptera declined as a negative exponential function, and Simuliidae did not decrease with lateral distance. Sex ratios typically were strongly biased, possibly a result of the harsh terrestrial environment negatively influencing the naturally more sedentary sex (which varies among taxa). In 2003, the majority of common species emerged approximately one month later than in 2002, and abundance and diversity were greater in 2003 than 2002, patterns potentially attributable to increased snowpack amount and duration. Late-emerging species, by contrast, were less abundant in 2003, likely because that year emergence was delayed to later in the season, when cooler air temperatures reduce flight activity. Our results suggest that alpine streams are sensitive to interannual variation in snowpack, and therefore more research will be needed to address the potential effects of climate change and associated winter snowfall trends on these unexpectedly diverse aquatic systems.
Research conducted with the communities of Igloolik, Ulukhaktok, and Churchill in northern Canada documents increasing exposure to hazards associated with ice use for hunting and travel. This trend is related to changing ice conditions. Instrumental records show later ice freeze-up and earlier breakup since the late 1970s, increasing temperatures, and changes in weather in the case study communities. Elders and mature community members, drawing upon their traditional knowledge, describe similar changes in ice and other climate-related conditions in recent years. These changes are increasing the risks of utilizing the ice for hunting and travel and they are reducing access to traditional food. Change in risk-taking behavior among users of the ice has also been documented in Igloolik and Ulukhaktok over the last few decades and has shaped the implications of more recent changes in ice conditions. Comparison between the communities reveals uneven consequences of changing ice conditions which is linked to the nature of ice use, local physiological setting, and community socio-cultural dynamics.
Infrared differential thermal analysis (IDTA) was used to study ice propagation and whole plant freezing patterns in dehardened intact individuals of various alpine plant species, including a shrub (Rhododendron ferrugineum), a herbaceous plant (Senecio incanus), a cushion plant (Silene acaulis), and two graminoids (Poa alpina and Juncus trifidus). Freezing patterns differed markedly among species and reflected peculiarities of the shoot structure and the vascular system. In graminoids, each single leaf required a separate ice nucleation event, as the polystele prevents ice propagation between leaves via the stem. Additionally, enhanced supercooling resulted in a temperature range of whole plant freezing of up to 10°C, which corroborates the high summer frost resistance of graminoids. This could have ecological significance for frost survival. In contrast, in dicotyledonous species one nucleation event was usually sufficient for whole plant freezing. Controlled ice-seeding experiments on leaves with droplets of water and bacterial water suspension (Pseudomonas syringae) showed that ice propagation into the leaf tissue from the surface was inhibited as long as the leaves were undamaged. The rate of ice propagation in veins was significantly higher at lower temperatures and reached up to 24 cm s−1 in J. trifidus, which is much higher than reported in earlier findings. Ice propagation in graminoids was much faster, which may indicate that ice propagates within the protoxylem lacunae of large vessels.
What do members of the general public know about polar regions, and how much do they care? Who knows or cares? This paper explores data from the General Social Survey (GSS), which in 2006 questioned a representative sample of more than 1800 U.S. adults about their knowledge and opinions concerning polar regions. The polar survey items were modeled on long-running GSS assessments of general science knowledge and opinions, recently summarized in the U.S. National Science Board's report Science and Engineering Indicators 2008. Polar knowledge proves to be limited but certainly not absent among survey respondents. Polar knowledge, general science knowledge, and education—together with individual background characteristics (age, sex, income)—predict policy-relevant opinions. Political orientation filters the impacts of education, and also shows consistent, significant effects across all the polar opinion questions. These 2006 GSS polar results will provide a baseline for comparison when the questions are repeated on a 2010 survey, after the International Polar Year concludes.
We examined the relationship between plant community diversity (species richness, evenness) and stability in an alpine Dryas octopetala heath exposed to four years of warming (open top chambers) and nutrient addition at Finse, southern Norway. Furthermore, we examined if different functional types responded differently to the interaction between environmental change and initial community diversity. We used the temporal change in species composition, calculated as the sum of change in sample scores in detrended correspondence analyses, as a measure of variability (opposite of stability). Under ambient conditions, a high initial species richness was associated with less stability of the total species composition. Under experimental warming, initial high species richness and evenness were associated with a more stable subsequent vascular species composition. Vascular stability decreased, however, with higher species richness under nutrient addition. When warming and nutrient addition were combined, high initial evenness was associated with more stable bryophyte composition, whereas high species richness was associated with reduced lichen stability. Thus, the degree and direction of the diversity-stability relationship depended on the type of environmental perturbation, the responding functional type, and on the diversity parameter used. The large variation in diversity-stability relationships is likely an outcome of complex species interactions and environmental factors influencing community diversity.
Rock outcrops cover large areas of alpine headwaters and are entrenched by chutes and couloirs, which are controlled by faults in bedrock. These widespread landforms play an important role in delivering sediment to lower basin slopes. High-resolution topographical data from LiDAR surveys allow investigation of morphometric characteristics and sediment transport processes in these features. Using aerial photo interpretation, field surveys, and topographic analyses of LiDAR data, this paper quantifies the morphological characteristics of rocky couloirs and their drainage basins, and the relationship between these features and the structural setting, in a study area in the Dolomites (northeastern Italy). Rock basins are characterized by small sizes (surface area < 0.066 km2) and high average basin slopes (up to 2.1 m m−1). The analysis of contributing area and local slope outlines the difference between these rock basins, and even smaller and steeper rock faces entrenched by very shallow chutes, which were defined as interbasin areas. We consider rocky couloirs and rock basins in the headwaters of the Dolomites to be part of the channel network, since channeled flow occurs in the couloirs during storms. High-intensity rainstorms trigger debris flows as evidenced from local scouring, especially in the lower parts of the couloirs. The longitudinal profiles of the couloirs are overall linear, but the high-resolution data display distinct high-slope and low-slope stretches forming steps, that may function as localized sources and sinks for debris flows. The cross-sectional widths of the couloirs do not appear related to upslope area; this may be due to both structural control on cross-sectional geometry and complex erosion of the couloir by debris flows.
Dating of past glaciation in New Zealand allows Quaternary climatic events to be identified in areas at a great distance from northern hemisphere ice sheets and associated climatic feedbacks. Moreover, climate reconstruction in New Zealand provides insight into the amount of climate change that occurred in the Southwest Pacific where zonal circulation is an important integrator of the climate signal. Boulder Lake is a relatively low-elevation cirque in a range of moderate-relief (∼1600 m) mountains in South Island of New Zealand, and it experienced cirque and valley glaciation during the Late Quaternary. Geomorphic mapping, 10Be and 26Al exposure, and luminescence dating provide evidence for glacial advances during the Last Glacial Cycle, specifically during Marine Isotope Stage 4 (MIS 4) and Marine Isotope Stage 2 (MIS 2). The MIS 4 advance was fractionally larger and is dated by a former ice-marginal lacustrine deposit (minimum age) with a basal Optically Stimulated Luminescence (OSL) sediment deposition age of 64.9 ± 10 ka. Paired 10Be and 26Al constrain a slightly less extensive MIS 2 glacial advance to 18.2 ± 1.0 and 17.8 ± 0.9 ka, coincident with the Last Glacial Maximum (LGM). Glacial equilibrium-line altitudes during both MIS 4 and MIS 2 phases were ∼960 m lower than the present. This corresponds to a cooling of 5–7°C, taking possible precipitation variability into account. Our findings and a growing number of publications indicate that many temperate valley glaciers reacted differently to the major ice sheets during the Last Glacial Cycle, reaching their maximum extent during MIS 4 rather than during peak global ice volume during MIS 2.
Environmental change, caused by nitrogen deposition and temperature increase, is predicted to affect allocation to carbon-based secondary compounds (CBSCs) in plants, due to changes in their internal carbon resources. The CBSCs are considered important for plant resistance to biotic and abiotic environmental stresses, such as herbivory, pathogen attacks, and UV radiation. To determine how allocation to putative defense compounds is affected by N deposition and increased temperature, we analyzed the composition of CBSCs in leaves of three arctic-alpine plant species: Bistorta vivipara, Dryas octopetala, and Salix reticulata after 5 years of warming (by open-top chambers) and experimental nutrient addition in an alpine Dryas heath in southern Norway. The dry weight of leaves increased after nutrient addition and warming combined with nutrient addition in all three species, while the weight of D. octopetala leaves also increased with warming alone. Individual chemical compounds or compound groups reacted to the treatments to different degrees and in different directions in the three species. The total concentration of CBSCs changed significantly only in S. reticulata, where it decreased in plots with nutrient addition combined with warming. Shading caused by taller vegetation in these plots might have bigger effects on the CBSC concentration than the direct changes in nutrient availability and temperature. Dryas octopetala had the highest concentration of CBSCs among the three species and was least affected by the treatments. Our results show that increased N availability and temperature influenced the level of carbon-based defense in some alpine plants but not others, indicating species-specific C-allocation responses to environmental change. Consequently, environmental changes may differentially affect defense abilities of alpine plant species, which could possibly contribute to future changes in interspecific competitive relationships and subsequently species composition of alpine plant communities.
Considerable spatial variability in snow properties exists within apparently uniform slopes, often resulting from microscale weather patterns determined by local terrain. Since it is costly to establish abundant weather stations in a region, local lapse rates may offer an alternative for predicting snowpack characteristics. For two Castle Mountain Resort weather stations, we present the 2003–2004 winter season weather and snow profile data and the 1999–2004 winter season lapse rates. A third site was sampled for small-scale spatial variability. Layer thickness, stratigraphy, temperature gradients, crusts, wind drift layers, stability, and settlement were compared between the sites and correlated with temperature, wind, and lapse rates. Average yearly snowfall was 470 cm at the Base and 740 cm at the Upper station. Average daily maximum and minimum temperature lapse rates are −6.1°C km−1 and −5.7°C km−1 when inversions are removed. Inversions occur mostly at night, adversely affecting lapse rate averages. Lapse rate modes are unaffected and most often −6.3°C km−1. Snowpack spatial variability is ∼25% of layer thickness and is controlled by wind and topography. Layer settlement is primarily related to initial snow thickness and wind drift. Snowpacks stabilize with age, unless rain crusts are present, which are important low-force failure horizons.
QEMSCAN®, an automated scanning electron microscope, is used to provide a high-resolution analysis of eolian sands collected from Victoria Valley, McMurdo Dry Valleys, Antarctica. This technique provides a rapid, digital, quantitative morphological and mineralogical analysis of sediments, originally developed for the mining industry, which we apply for the first time to the study of eolian sand transport. Results show fine to medium-sized sands (<300 µm) are similar in shape and mineralogy throughout the hyper-arid landscape of the Victoria Valley. We relate this to the almost continuous mixing of fine-grained sediments in the mostly snow- and ice-free valley by frequent thermally induced easterly winds and less common but stronger topographically channeled southwesterly foehn winds. Analysis of local dune sands transported during easterly winds, which typically just exceed the local threshold entrainment velocity of 5.3 m s−1 (at 0.4 m), indicate preferential transport of quartz grains by these winds. Surface type was found to exhibit considerable influence over the characteristics of eolian sand transport with much larger grains carried in saltation and modified suspension above fluvio-glacial outwash surfaces than above sand dunes. Results illustrate the potential of QEMSCAN as an effective tool for multi-parameter analysis of eolian sands allowing greater insight into the controls on eolian sand transport in settings such as the Victoria Valley, Antarctica.
Monitoring studies show that many mountain glaciers worldwide are decreasing in mass. An important component of the process of ice mass loss is the effect of dust on albedo and its effect on glacier mass balance. The characteristics of surface dust were investigated in August 2006 on the Ürümqi Glacier No. 1 in the Tien Shan Mountains, China. The bare ice surface of the glacier was mostly covered by brown dust. The amounts of surface dust on the ice surface (dry weight) ranged from 86 to 1113 g m−2 (mean: 335 g m−2, standard deviation: = 211), which is within the normal range for Asian glaciers, but significantly greater than those on glaciers in other regions such as Alaska, Patagonia, and the Canadian Arctic. An analysis of organic matter and microscopy of the surface dust revealed that the dust contained high levels of organic matter, including living cyanobacteria. This suggests that it is comprised not only of deposits of wind-blown desert dust, but is also a product of microbial activity on the glacier itself. Spectral albedo of the glacial surface showed spectrum curves typical of those of snow and ice contaminated with dust. The integrated surface albedo ranged from 0.09 to 0.24 (mean: 0.14) in the ice area, from 0.50 to 0.64 (mean: 0.56) in the snow area. The lower albedo on the glacial surface compared with that of clean bare ice or snow surface suggests that the albedo was significantly reduced by the surface dust on this glacier. Results suggest that the mineral and organic dust on the glacial surface substantially accounts for the recent shrinkage of the glacier.
Using the High Sudetes as an example, we examined whether the position of the alpine treeline is in fact related to the heat load of the site, and whether the temperatures of the air and soil change along slopes with differing exposure to solar radiation. We hypothesized that if there are really strong exposure effects they must be expressed both in significant correlations between treeline elevation and heat load of respective sites and in distinct differences in root zone and tree top temperatures. We found that the highest positions of the alpine treeline were situated in places with the potentially highest heat load. Nevertheless, only weak exposure effects on the soil temperatures during the growing season were detected, both in the closed forest and in the tree groups. Further, air temperatures near the terminal shoots varied significantly less than soil temperatures; however, the margins of the closed forest were especially more favorable at the south-facing slopes. Winter soil temperatures did not seem to be generally more advantageous on sites with high heat load. Direct temperature measurements thus indicated that established positions of the alpine treeline are just slightly influenced by differences in heat load.
Geographic variations in summer (July–August) precipitation data for the northern Qinghai-Xizang (Tibetan) Plateau, collected during the IOP (Intense Observation Period) of GAME-Tibet, were examined. Results indicated that, basically, the daily precipitation amount consistently varies temporally at all sites. An increase in precipitation amount is evident from north to south. The distribution of summer monsoon precipitation is affected by latitude, altitude, and other factors (i.e. atmosphere circulation, water vapor transportation). The latitude effect of precipitation in July and August was significant. August precipitation varied with both latitude and altitude. The site with higher elevation received more precipitation. Topoclimatic controls operating over precipitation on slopes include elevation. The distribution of the precipitation during July–August mainly showed the effects of latitude, but this was modified by the altitude effect. Redistribution processes caused by topography induce increased precipitation with altitude at some sites. Owing to the complexity of surface conditions on the Qinghai-Xizang (Tibetan) Plateau, precipitation is controlled by many factors simultaneously. Without benefit of an expanded observation network, it is difficult to separate the effects of the many factors influencing the distribution of precipitation in the region.
This study tested the hypothesis that the thickness of the pollen wall will increase in response to enhanced UV-B irradiation, by examining the effect of enhanced UV-B irradiance on the pollen morphology of Salix polaris Wahlem. grown in a field experiment on the Arctic tundra of Svalbard. Measurements of pollen morphology were conducted by light microscopy on plants grown at two sites, Adventdalen and Isdammen. Salix vegetation was grown under control, enhanced UV-A, and two enhanced UV-B (simulating 15 and 30% reduction in the thickness of the stratospheric ozone layer) treatments. At the Adventdalen site, pollen wall thickness significantly increased under enhanced UV-A and UV-B treatments compared with the control. A thicker pollen wall helps to prevent damage by UV-B radiation of the DNA of the pollen. In contrast, plants at the Isdammen site did not exhibit any significant pollen morphological response to the enhanced UV treatments. The inconsistency in plant response to enhanced UV treatments between the two sites may be explained by greater habitat heterogeneity at the Isdammen site; abiotic soil conditions including nutrient and water availability may also have an influence on pollen morphology.