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Biological soil crusts (BSCs) are small-scale communities of lichens, mosses, algae, and cyanobacteria that cover much of the surface area in regions where vascular plant growth is restricted due to harsh environmental conditions, such as perpetually ice-free areas in terrestrial Antarctic environments and alpine areas above the tree line. To our knowledge, none of the available studies provides a direct Antarctic-alpine comparison of BSC activity periods and the water use, both key traits to understand their physiological behavior and therefore related growth and fitness. Here, activity patterns and water relations were studied at two sites, one in continental Antarctica (Garwood Valley 78°S) and one in the High Alps of Austria (Hochtor, Großglockner 2350m). BSCs in continental Antarctica were only rarely active, and if so, then during melt after snowfalls and by fog. In the Austrian Alps, BSCs were continuously active and additionally activated by rainfall, fog, and dew. Consequently, high alpine BSCs can be expected to have much higher photosynthetic productivity supporting higher growth rates than the same functional vegetation unit has in continental Antarctica.
Shrub willows (Salix species) are widespread beyond the latitudinal and altitudinal treelines. Their ring width has been shown to be a reliable ecological indicator for changes in the harsh cold conditions in the Arctic, but little is known on their growth in alpine conditions. The shrubby Salix oritrepha grows above the treeline on the northeastern Tibetan Plateau (TP), making it an interesting woody species to explore responses of alpine communities to ongoing climate warming in this area. Since precipitation increases with increasing elevation (until 4670 m) in the study area, we hypothesize that the growth of S. oritrepha is mainly constrained by cold summer temperature. We sampled 35 S. oritrepha individuals above the juniper treeline (4200 m), and took basal wood cross sections for dendrochronological analyses. Few missing rings were detected at the shoot base when serial sectioning was applied. Ring width (RW) and basal area increment (BAI) standard chronologies were established. We found that BAI reflected a stronger climatic signal than RW. The radial growth was constrained by low July to August temperatures. We expect that climate warming would enhance the growth of alpine willows, which could alter the services provided by these high-elevation ecosystems.
We studied the vegetation cover of 60-year-old military sites in the subarctic mountain area in northwestern Finnish Lapland, comparing the vegetation of observation posts in the barren mountain and camps in the mountain birch zone to the undisturbed control sites. These kinds of old disturbance areas give us valuable information about resilience and recovery of vegetation in a fragile subarctic environment and allow us to follow up and predict changes under changing climate.
Vegetation of the disturbed sites had not recovered to the initial condition in 60 years; the recovery was slower in the mountain birch zone where the intensity of disturbance had been higher. The coverage of dwarf shrubs, especially Empetrum hermafroditum and Vaccinium myrtillus, was lower at the military sites as compared to the controls; instead, increased coverage of some graminoids was observed in the observation posts and the transition zones of camps. At the most disturbed patches, cryptogams were still prevailing. The results confirm the observations of earlier studies that rather than ecological recovery, the long-term development of vegetation in disturbance areas in high latitudes shows a shift to functionally different plant communities.
Cushion plants in alpine ecosystems act as nurse species, which modify and alleviate environmental conditions and positively influence the diversity and abundance of other organisms. Soil fauna in alpine environments should benefit from nurse plant facilitation, but this has not been investigated. We compared diversity, abundance, and community structure of soil microarthropods (Collembola, Oribatida, Mesostigmata, Prostigmata, Endeostigmata, and Astigmata) under cushion plants and in adjacent open microsites in high altitude patterned ground landscapes in New Zealand. We investigated how cushion plants influence environmental factors, and how environmental factors and species traits contribute to microarthropod community structure. The results show that cushion plants are a key in maintaining the biodiversity of soil microarthropods in the high alpine. Cushion plants maintain higher moisture and organic matter content in the soil, provide productive and structurally complex habitat, and mitigate disturbance. Abundance and species richness of Oribatida, Mesostigmata, and Prostigmata were higher under cushion plants. In contrast, abundance of Collembola was higher in open microsites, while their species richness similar in and out of cushions. Oribatida assemblages were dominated by small asexual species, indicating a disturbed environment. Oribatida community structure was significantly related to the microhabitat in two out of three mountain ranges. Collembola assemblages were similar in and out of cushions. Higher soil moisture and organic matter content under cushion plants were significant in explaining patterns in microarthropod assemblages, although high percentage of variability was not explained by environmental variables. There was no effect of cushions on soil temperatures. Species identity of the cushion plant did not influence abundance, species richness, or community assemblages of mites and springtails; however, some species were associated with either Dracophyllum or Raoulia cushions.
Soil properties in alpine treeline ecotones are insufficiently explored. In particular, an extensive monitoring of soil moisture conditions over a longer period of time is rare, and the effects of soil moisture variability on alpine treelines have not received adequate attention yet. Soil temperature patterns are generally well documented, and soil temperature is considered a key factor in limiting tree growth at both global and local scales. We performed a 2½-year monitoring in a near-natural treeline ecotone in Rolwaling Himal, Nepal. In this paper, we present new findings on spatiotemporal soil temperature and moisture variability in relation to topographical features and vegetation patterns (variations in stand structures and tree physiognomy). Our results show a growing season mean soil temperature of 7.5 ± 0.6 °C at 10 cm depth at the Rolwaling treeline. Multivariate statistical analyses yield a significant relation between soil temperatures and the variability in tree height, crown length, crown width, and leaf area index (LAI). In turn, soil temperature variability is controlled by the tree physiognomy itself. Soil moisture conditions (available water capacity, 0–10 cm) appear to be less substantial for current stand structures and tree physiognomy. In turn, tree physiognomy patterns control soil moisture, which additionally is affected by snow cover. In Rolwaling, shallow and coarse-grained soils cause low water-holding capacities, and thus a remarkable amount of water percolates from topsoils to subsoils. In the alpine tundra with missing forest canopy, year-round lowest available water capacities are additionally caused by high solar radiation, wind, and thus high evaporation. We assume low soil moisture availability causing largely prevented tree regeneration especially in the alpine tundra.
We conclude that soil temperature and moisture patterns reflect tree physiognomy patterns. The latter cause disparities in soil temperature and moisture conditions inside and outside of the closed forest by shading effects and differences in leaf fall.
The locally migratory behavior of the high arctic muskox (Ovibos muschatus) is a central component of the breeding and winter survival strategies applied to cope with the highly seasonal arctic climate. However, altered climate regimes affecting plant growth are likely to affect local migration dynamics of the muskox. In this study, we apply long-term local-scale data on the seasonal distribution of muskoxen in the Zackenberg Valley, Northeast Greenland, to assess the degree of climatic influence on local seasonal muskox dynamics. Specifically, we analyze how seasonal climate (temperature, snow cover), forage availability (length of growth season), and the number of adult females available per male (operational sex ratio) influence changes in the seasonal density dependence, abundance, and immigration rate of muskoxen into the valley.
The results suggested summer temperature as the major controlling factor in the seasonal, local-scale migration of muskoxen at Zackenberg. Specifically, higher summer temperatures, defined as the cumulative average daily positive degrees in June, July, and August, resulted in decreased density dependence and, consequently, increase in the seasonal abundance of muskox in the valley. Additionally, a longer growth season was found to increase the seasonal abundance of muskox in the Zackenberg Valley. In contrast, changes in spring snow cover displayed no direct relation to the seasonal immigration rate. Our study suggests that access to high-quality forage is important for the short-term, local scale population dynamics of muskoxen in Northeast Greenland.
Recent studies suggest that climate changes may have a strong impact on the vegetation composition in Arctic ecosystems, causing increasing dominance of woody species. Evidence from short-term studies on the effects of herbivory indicates that this effect may be counteracted by grazing, but it has not yet been studied whether the effect is persistent and general. Here, we present the results from a large-scale, long-term study of the effects of sheep grazing and climate on the relative dominance of woody plants, graminoids, and forbs. The study is based on exclosures established from 1984 onward across a climatic gradient in South Greenland. The relative cover of the three plant functional types was modeled in a state-space model. There was no significant overall change in the relative cover of the three groups, although such changes occurred intermittently on some sites. This suggests that the relative dominance of the plant functional types is resilient to the impacts of grazing and climate changes in the tundra of South Greenland in line with other studies from sites where summer temperatures have not increased.
More than 5000-yr-old organic material was released by a melting glacier in central southern Norway. The ancient carbon was bioavailable and supported early food chains. This was shown through high radiocarbon age in living aquatic and terrestrial invertebrates. Young ponds acted as biological oases, where ancient carbon was assimilated by larvae of various Diptera: mainly Chironomidae, but also Tipulidae and Limoniidae. Within ponds, even predatory diving beetles had a high radiocarbon age. Adult chironomid midges with a radiocarbon age of 1040 yr transported ancient carbon to terrestrial predators among beetles, spiders, and harvestmen. Ancient carbon was also assimilated by chironomid larvae downstream in the glacier-fed river, and radiocarbon dating of chironomid larvae from glacial rivers will thus be an easy way to check whether a given glacier releases bioavailable ancient carbon. Our study indicates that the ancient organic particles were very small. We refer to studies from other countries showing that glaciers collect and release ancient carbon in the form of tiny, long-transported and biodegradable aerosol particles, which stem from the incomplete combustion of radiocarbon-depleted fossil fuels. All our results would fit with this mechanism.
Water isotopes play an important role in the study of the alpine lake water budget and the hydrological cycle in the arid, far western Tibetan Plateau. These isotope records, derived from well-preserved sediments, are believed to reflect climatic and environmental changes. Using two years of δ18O and δD data from precipitation, river water, underground water, and lake water at the long alpine lake Bangong (LBG), together with local meteorological observations in the arid western Tibetan Plateau, this study reveals that the δ18O in the lake is over 10‰ more enriched than that in the local precipitation due to evaporation of the lake water. Spatial changes in both the lake water δ18O and d-excess (= δD - 8 * δ18O) are apparent, ranging from ∼-4.9‰ to 0.9‰ for δ18O, and -13.22‰ to -30.85‰ for d-excess, respectively, from east to west of the lakes. Simulation with the Craig-Gordon model shows that the isotopes in alpine inland lake water are controlled to a great extent by local relative humidity. Using a modified partly mixed isotope fractionation model, we rebuilt the spatial change of the evaporation/inflow (E/I) ratios from east to west of the lake. A quantitative estimation shows that the E/I ratio of the lake water increases from 0.73∼0.83 in the eastern part and 0.90∼0.93 in the western part of LBG. We also found that by assuming a full development of kinetic fractionation of the environmental vapor isotopes, our simulation result matched the observed spatial change for both δ18O and d-excess, confirming the strong inland evaporation enrichment in the northern part of the plateau. This research may increase our understanding of inland water movement in the alpine Tibetan lakes, and also will improve our understanding of the lake sediment isotope record.
Change detection studies using remote sensing and plot-based sampling show that Arctic vegetation is changing. Most studies have focused on the proliferation of tall shrubs, but increased productivity in areas where shrub cover is low suggests that other functional groups may also be changing. To investigate vegetation change across the Tuktoyaktuk Coastlands we analyzed high-resolution repeat air photos from 1980 and 2013. Thirty-eight image pairs were used to estimate changes in the cover of six functional groups (tall shrub, dwarf shrub, non-tussock-forming sedge, tussock-forming sedge, moss, and lichen). The spatial extent of our airphotos allowed us to investigate changes across four terrain types (high-center polygonal terrain, low-center polygonal terrain, shrub tundra, and tussock tundra). Our analysis shows that all four terrain types experienced absolute increases in shrub cover ( 7.71% to 11.98%), with the expansion of dwarf shrubs playing an especially important role in regional change. Significant declines in lichen cover were also observed. While the consistency of shrub encroachment across terrain types suggests that changes were facilitated by shifts in broad-scale processes like temperature or precipitation, our data also indicate that differences in the magnitude of change were mediated by community structure and the availability of suitable microsites.