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In permafrost-affected sites, soil forming processes appear to be closely connected with organic matter (OM) accumulation. In this work OM composition and nutrient availability has been evaluated in a frost-affected soil located at 1200 m a.s.l. in Creux du Van (Switzerland), where patches of stunted Norway spruce trees adjacent to tall trees have been ascribed to the presence of sporadic alpine permafrost. Soil samples were collected under the stunted forest and in the adjacent tall forest and characterized for their chemical and physical characteristics. The main C and N forms have been determined and characterized.
Under the stunted forest the soil samples showed a high total organic C/total N (TOC/TN) ratio and scarce microbial activity; humification processes were limited and humic acids revealed little oxidation, scarce incorporation of N-containing moieties, and high enrichment of lipids. 14C dating revealed the presence in the bulk samples of young organic material mixed with relatively old humic acids, probably due to cryoturbation processes. These latter processes appeared also responsible for the arrival of fresh litter material from Oi and Oe horizons into the Oa horizon of the stunted forest and for the consequent genesis of humic substances from a mix of old and fresh residues.
From our findings there seems to exist a reciprocal influence of vegetation quality on the OM composition, and of OM decomposition on nutrition, as driven by the microclimatic conditions and physical processes, which in turn may contribute to keep the soil at an unstable developmental stage and limit the spruce growth.
Space-borne remotely sensed data can provide valuable insight into cryospheric processes in remote high-latitude regions for which direct observations are limited. In this study we use synthetic aperture radar (SAR) and Landsat imagery to evaluate recent changes in the ice cover of Upper and Lower Murray Lakes (81°20′N, 69°30′W) on Ellesmere Island, Nunavut, Canada. These data highlight changes in ice conditions that have occurred over the past decade and provide a means for assessing the likely impacts of rising temperatures on future lake-ice conditions. Under current (1997–2007) climatic conditions the Murray Lakes average several weeks of ice-free conditions in August and early September, although in some years a partial ice cover persists throughout the year. The observed relationship between summer temperature and ice melt at Upper and Lower Murray Lakes suggests that recent warming in the High Arctic has forced the lakes near a threshold from a state characterized by perennial ice cover to the current state that includes seasonal melting of lake ice. Projected future warming will significantly increase the duration of ice free conditions on Upper and Lower Murray Lakes, with ice-out predicted to occur 13.5 ± 4.0 and 17.6 ± 5.6 days earlier, respectively, for every 1 °C increase in mean June–July temperature.
An ecological analysis of wetlands in the high mountain jalca above 3700 m elevation in the Andes near Cajamarca, Peru, indicated that most wetlands are groundwater-supported peat-accumulating fens. The floristic composition of fen communities was controlled largely by groundwater chemistry, which was highly variable and influenced by watershed bedrock composition. Watersheds with highly mineralized rock discharged water as acidic as pH 3.7, which was high in CaSO4, while watersheds with limestone, marble, and skarn produced groundwater as basic as pH 8.2 and high in CaHCO3. Of the 125 plots sampled in 36 wetland complexes, >50% of plots had at least 3 m of peat, and 21 plots had peat thicker than 7 m. Most soil horizons analyzed had 18 to 35% organic carbon, indicating high C storage. A total of 102 vascular plants, 69 bryophytes, and 10 lichens were identified. Study plots were classified using TWINSPAN into 20 plant communities, which were grouped into four broad categories by dominant life form: (1) cushion plant communities, (2) sedge- and rush-dominated communities, (3) bryophyte and lichen communities, and (4) tussock grass communities. Direct gradient analysis using canonical correspondence analysis indicated that Axis 1 was largely a water chemistry gradient, while Axis 2 was a complex hydrology and peat thickness gradient. Bryophytes and lichens were more strongly separated in the ordination space than vascular plants and were better indicators of specific environmental characteristics.
Surface height and mass balance changes of Taku and Lemon Creek Glaciers within Juneau Icefield, Alaska, are examined to determine the relationship between these parameters and climatic forcing. Both Taku and Lemon Creek Glaciers are located in a maritime climate, but they behave very differently. Taku Glacier, a former tidewater glacier, is ∼70 times larger than Lemon Creek Glacier, and its dynamics are largely a result of the post-tidewater glacier cycle which causes insensitivity to climate change during advance phases. Taku Glacier is advancing at present but its surface height, mass balance, and rate of advance have decreased since 1988. Lemon Creek Glacier, a small alpine glacier, is retreating and has maintained a negative mass balance since 1953. Mass balance records from both Taku and Lemon Creek Glaciers correlate well with temperature and show little correlation with precipitation. The mass balance of these glaciers also correlates with the Pacific Decadal Oscillation (PDO). However, the Lemon Creek Glacier mass balance record shows a stronger correlation with the PDO than that of Taku Glacier. Taku Glacier shows a longer delay in response to warming in Southeast Alaska likely due to post-tidewater glacier dynamics, its large accumulation area ratio (AAR), and its size.
We focused on the mediating role of slope aspect and spatial pattern on upper treeline ecotonal dynamics at multiple spatial scales in the Southern Rocky Mountains to infer process interactions and gauge the importance of feedbacks in determining the potential response of upper treeline to climate change on contrasting south- and north-facing slopes. Dendroecological techniques were used to reconstruct tree establishment within the upper treeline ecotone and Ripley's K was used for spatial pattern analysis. Tree age was determined by using age to coring-height corrections, and the influence of slope aspect was quantitatively assessed at multiple spatial scales using Mann-Whitney U-Tests. Widespread tree establishment occurred within the treeline ecotone on both south- and north-facing slopes during the 20th century, but tree ages above timberline are significantly younger on north-facing slopes at all spatial scales (local, landscape, and regional). The spatial pattern of tree establishment above timberline was predominantly random, except for significant clustering on south-facing slopes in the Sangre de Cristo Mountains. The aspect mediation of tree age and spatial pattern suggest that the importance of feedbacks may vary according to slope aspect and that both of these environmental factors should be considered when assessing possible treeline response to climate change.
We examined sediment melt-migration dynamics in the ice cover of Lake Fryxell, Taylor Valley, McMurdo Dry Valleys, Antarctica, using a combination of laboratory experiments, field observations, and modeling. The specific objectives were to determine the thermal conditions required for sediment melt and how sediment migration rates vary with meteorological forcings and ice microstructure. These characteristics are relevant to the influence of climate change on lake ice structure and ecosystem processes in polar regions. Sediment began melting through laboratory ice at −2 °C in simulated summer conditions, with warmer ice producing faster melt rates. An energy balance model, supported by our laboratory experiments, demonstrated that subsurface sediment can melt down to an equilibrium depth of ∼2 m in two years. Field experiments and modeling revealed that surficial sediment melts at about half the rate of subsurface sediment because of heat losses to shallow, cold ice and the cold, dry atmosphere. Gravity flow of sediment along grain boundaries was pronounced in laboratory ice warmer than −1 °C. This mechanism produced a flux of 0.1 g m−2 hr−1, a significant value relative to published benthic sedimentation rates for these lakes indicating an important sediment sorting mechanism.
This paper describes a micromorphological investigation of an early Holocene loess-paleosol sequence at the Chena Hot Springs Road site, a highway road cut exposure near Fairbanks, Alaska, U.S.A. The procedure identified and described soil microstructure, basic mineral components and their related distributions, organic inclusions, and pedogenic features. Micromorphology confirmed the presence of a number of thin, discontinuous, weakly expressed soils that evince disturbance by diagenetic, graviturbative, and cryoturbative processes. Well-preserved organic remains indicate the presence of a boreal forest that would have acted as a highly effective sediment trap. The frequent observation of detrital iron-oxide grains is consistent with other studies of area loess that reveal high concentrations of magnetite and ilmenite, resulting in significant increases in magnetic susceptibility. Increases in wind strength are likely responsible for the increased clay content in the buried paleosols. Loess deposition, which would inhibit pedogenesis, is probably related to greater wind strength, while pedogenesis, indicative of stability and minimal deposition, suggests periods of reduced wind.
We used a rapid assessment to survey American pika (Ochotona princeps) populations and documented 420 pika site occurrences in southwestern U.S.A. These included 329 sites from the Sierra Nevada (SN), California; 67 from six southwestern Great Basin (swGB) ranges, California and Nevada; 16 from three central Great Basin ranges, Nevada; and 8 from the central Oregon Cascades. Of these, 67% were currently occupied, 27% modern (indirectly scored active), and 6% old. Sites were grouped into 148 demes, 88 regions, and 11 mountain ranges. Current elevations ranged from 1645 m (1827 m excluding Oregon) to 3887 m, extending the lower elevational range of the species at the study latitude. Sites were distributed on all slope aspects with a preference for north to easterly aspects, and without preference for substrate. Rock-ice-feature (RIF) till, notably rock-glacier and boulder-stream landforms, accounted for 83% of the sites. Climatic relationships from the PRISM model for the SN and swGB sites showed wide tolerance, with average precipitation 910 mm, average minimum temperature −3.9 °C, and average maximum temperature 8.7 °C. Average minimum temperatures for old sites were not significantly different from recent sites, whereas average maximum temperatures were significantly higher in old sites. Unusual features of RIF landforms make them important refugia for pikas as climates warm. In contrast to studies that document species vulnerability elsewhere, pikas in the SN and swGB appear to be thriving and tolerating a wide range of thermal environments.
We examine trends in surface air temperature for the San Juan Mountain region in southwestern Colorado from 1895 to 2005. Observations from both National Weather Service (NWS) and Snow Telemetry (SNOTEL) sites are analyzed. Results show a net warming of 1 °C between 1895 and 2005. Most of this warming occurred between 1990 and 2005, when the region experienced rapid and secular increases in temperature. Between 1950 and 1985, there was a cooling trend in the region during which there were significant decreases in the maximum temperature (Tmax) and almost no trend in the minimum temperature (Tmin). This cooling trend appears to be, in part, associated with increases in atmospheric aerosols. Between 1990 and 2005, the large increases in temperature anomalies are strongly correlated at the NWS and SNOTEL sites. Annual increases in Tmax and Tmin are similar between 1990 and 2005; however, they generally show greater increases during summer and winter, respectively. Spatially, there are similar increases in Tmax and Tmin except in the central mountain region, where the increases in Tmin are larger and started earlier.
In mid-February 2006, windstorms in Arizona, Utah, and western Colorado generated a dust cloud that distributed a layer of dust across the surface of the snowpack throughout much of the Colorado Rockies; it remained visible throughout the winter. We compared the chemical composition of snowfall and snowpack collected during and after the dust deposition event with pre-event snow at 17 sites extending from central Colorado into southern Wyoming. The chemistry of dust-event snowfall and the post-event snowpack were compared to long-term wetfall precipitation and snowpack chemistry at the Fraser Experimental Forest (FEF). The pH of the snowpack formed during the dust event was 1.5 units higher, calcium was 10-fold higher, and acid neutralizing capacity (ANC) was 100-fold higher than levels measured in either early or late-season snow. Elevated ANC was attributable to dust-derived increase in carbonate/bicarbonate ions, likely from soluble calcium carbonate inclusions in dust material. The single dust event contributed carbonate/bicarbonate-derived ANC equivalent to the sum of strong acids deposited during the entire winter at FEF. Effects appeared more pronounced at upper elevations and in the sparse forest near treeline, compared to densely forested lower elevation sites. Monthly snowpack solute analysis at FEF has not documented an event of similar magnitude during its 17-year period of record. The solute composition of post-event snow is similar to average Fraser streamwater, however. To assess the effect of dust on the timing and composition of water exported from high-elevation ecosystems, future work should consider both the contributions of eolian deposition on soil development, plant communities, and nutrient and water relations plus the impact of individual deposition events on snowpack chemistry and duration.
Studying intraspecific spatiotemporal variation in vital rates among populations over a range of environmental conditions is essential to reveal intrinsic and extrinsic factors affecting population dynamics. Mammal populations living at higher elevations often have higher adult survival, shorter breeding seasons, and lower reproductive output per season than at lower elevations. We studied dynamics of a Eurasian red squirrel (Sciurus vulgaris) population in high-elevation, mountain pine (Pinus mugo) forest with extreme winters, in the Central Italian Alps, and compared vital rates with populations in more productive habitats at lower elevations. Average density was 0.14 ± 0.07 squirrels ha−1 (range 0.07–0.30 ha−1), and numbers typically increased in summer–autumn as a result of seasonal reproduction and immigration. Mean persistence time was only 12.5 months, and there was a nearly complete population turnover in only two years. Local survival and recruitment rate were correlated with seasonal population growth rate, and partial effect of survival explained 80% of variation in growth rate. While reproductive rate in mountain pine habitat was more similar than in more productive habitats at lower elevations, density and autumn–winter survival were much lower. Thus, red squirrels did not show the adaptations observed in several other mammal species, but might invest heavily in early reproduction to compensate for short life expectancy.
We estimated the abundance of voles, or vole nests, in four different experiments in the Boreal forest understory in the southwestern Yukon to test if voles were attracted to fertilizer. In one experiment we counted vole nests in plots that had been fertilized or not fertilized for 4 years; in a second we counted trapped voles in plots that has been fertilized, or not, for 13 years; and in two others we counted the number of vole visits to Longworth traps baited with fertilizer. There were significantly more over-winter nests in the fertilized plots. In a June trapping session, more voles were captured in fertilized plots than unfertilized plots and voles entered locked-open traps and removed fertilizer. The results demonstrate a relationship between fertilizer and voles. Whether voles are attracted to the fertilizer alone or the higher quality feed it produces remains unclear. A plausible, yet untested, hypothesis is that the voles were consuming the fertilizer as a source of micro- or macronutrients.
The functioning of ecosystems is strongly correlated to soil temperature dynamics. Because only a few studies so far have investigated the spatio-temporal variability of alpine soil temperatures, we proceeded to analyze soil temperatures in a heterogeneous alpine landscape by means of a multi-scale approach. We combined vertical soil temperature gradients from surface to 15 cm depth, microspatial variability within small catchments, and altitudinal changes of a continental mountain system. We analyzed differences at single sites and at multiple spatial scales. We found that microtopographic site conditions dominated thermal changes along altitudinal gradients. The adiabatic lapse rate did not show high correlations with local soil temperature gradients. We used isopleth diagrams of soil temperature gradients and corresponding scatterplots of soil temperature gradients between each pair of sites and low alpine–middle alpine mountain couples to quantify these overlying phenomena. This enabled us to quantify the significance of soil temperature gradients across vertical soil profiles, topography, and altitude in order to facilitate future microclimate extrapolation and modeling in high mountain (alpine) landscapes. Such procedures are crucial for describing expected responses of alpine ecosystems to global climatic change.