Vol. 33, No. 3, August 2001
Geomorphic Evidence for Late Glacial Ice Dynamics on Southern Baffin Island and in Outer Hudson Strait, Nunavut, Canada (pp 249-257)
We here describe glacial geomorphology that sheds light on ice-dynamic conditions during the Noble Inlet advance, a glacial event involving northward ice flow across Hudson Strait and large-magnitude meltwater drainage across Meta Incognita Peninsula at around 8.9 to 8.4 14C kyr BP. Through airphoto interpretation and field inspection of key sites we mapped the glacial geomorphology of interior Meta Incognita Peninsula, the postulated terminal zone for northward expansion of ice from Quebec-Labrador during the Noble Inlet advance. A 170-km-long zone of glaciofluvial canyons, washing zones and boulder deltas was traced from Shaftesbury Inlet to Henderson Inlet. This zone reflects initial drainage across Meta Incognita Peninsula at >520 m elevation, followed by ice marginal drainage at progressively lower levels along the southern slope ofthe peninsula. The ice marginal outline required to explain the glaciofluvial zone is compatible with northward-trending striae previously reported from the southern coast of Meta Incognita Peninsula. A very large flux of meltwater across Meta Incognita Peninsula probably occurred because eastward supraglacial drainage on ice in Hudson Strait was temporarily impeded and steered northward by a raised ice surface level in outer Hudson Strait, induced by an enhanced outflow of ice from Ungava Bay.
Microscopic Analyses of Quaternary Glacigenic Sediments of Marguerite Bay, Antarctic Peninsula (pp 258-265)
Micromorphological analyses were carried out on a selection of thin-sectioned intervals of Deep Freeze 1985 cores from Marguerite Bay, Antarctic Peninsula, to test previous interpretations with respect to the local Quaternary glacial history. Results show that both deformed and pristine glacimarine deposits are preserved in the sedimentary record. Many of the deformational features that were recognized with the aid of the microscope were previously unidentified. Interpretations in this study are based on certain combinations of planar and circular microstructures. Some associations are clearly associated with the process of subglacial shearing, others with gravity-driven sediment movements or coring imperfections. The number of mass movement deposits identified in the record is significantly higher than in previous studies. Subglacially deformed sediments were found in cores from the southwest part of the bay. This thin section study supports scenarios suggesting the presence of grounded ice on the marguerite Bay continental shelf during the Last Glacial Maximum.
Recent Retreat Glaciar Nef, Chilean Patagonia, Dated by Lichenometry and Dendrochronology (pp 266-273)
This paper presents the results of a lichenometric and dendrochronological study of the recent retreat history of Glaciar Nef, an eastern outlet glacier of the Hielo Patagónico Norte. A 600-yr tree regeneration time, based on maximum tree age in the ancient forest, suggests that the forest-clad lateral moraines in the valley, southeast of the 19th century terminal moraine system, were formed some time before A.D. 1370. Dating estimates suggest that retreat from a 19th century maximum began around 1863, a decade or two earlier than the date established for other glaciers in the region, with glacier thinning near the ice front averaging 1.11 m yr-1 between 1863-1881. After 1884, retreat seems to have slowed, with glacier thinning averaging 0.09 m yr-1. Lichen and tree dating suggests that the glacier had retreated approximately 500 m by 1938; this estimate is supported by an aerial photograph showing a proglacial lake just beginning to form in 1944. Recent glacier movements around the Hielo Patagónico Norte are discussed and it is concluded that the general trend of glacier retreat around the icefield, beginning in the 1860s to 1870s, is consistent with Northern Hemisphere trends.
Lake Level Changes Indicated by Dendrochronology on Subfossil Pine, Jämtland, Central Scandinavian Mountains, Sweden (pp 274-281)
Not only do high-latitude tree-ring data reveal minor and major Holocene climatic variation, but the distribution in time of subfossil trees provides information about former tree-line fluctuation. Over 152 samples of Scots pine (Pinus sylvestris) were collected and measured from lake Lilla Rörtjärnen, situated close to the present treeline. Five floating chronologies were built spanning 498 B.C.-A.D. 19, A.D. 50-390, A.D. 431-884, A.D. 946-1256, and A.D. 1337-1865. The floating chronologies were crossdated with a dendrochronology from Torneträsk. No trees were dated from 20-49 A.D., 391-430 A.D., 885-945 A.D., and 1257-1336, A.D. The temporal distribution of pines in the lake suggests periods of intensive germination, with each phase occurring within 80 to 100 yr from the beginning of each floating chronology. At the end of each phase higher lake levels drowned trees close to the shore. Both the existence and the preservation of the dead pines is likely to have been controlled by changes in lake level.
Soil Carbon Sequestration by Holocene Fires Inferred from Soil Charcoal in the Dry French Alps (pp 282-288)
The current global carbon budget has a missing sink, which is believed to be in terrestrial ecosystems. At least one carbon sink, wood charcoal sequestrated in soil, remains poorly detailed. We estimate the wood charcoal-carbon content in soils located in dry valleys within the French Alps. Soils were sampled at five sites along altitudinal transects, from the conifer-dominated subalpine forests to the alpine grasslands. The five sites were distributed along a bioclimatic and biogeographic gradient from the southern Mediterranean to the northern continental Alps. The altitudinal distribution of charcoal exhibits the same pattern in the five sites, despite stand fire history, and regional bioclimatic and biogeographic differences. Charcoal concentrations are low (0.01 to 10 gchar m-2) in soils from the current treeless belt, while soils at lower elevation show high concentrations (10 to 2000 gchar m-2). The results suggest that the landscape structure determine the charcoal accumulation throughout variability of vegetation type and fire frequency. Charcoal concentrations recorded in the subalpine belt in the Alps are similar to those of Swedish boreal forests, but are 10 to 100 times lower than values from Mediterranean ecosystems. Dry to subhumid ecosystems contain subfossil carbon in the form of charcoal, which should be explicitly taken into account in the global carbon budget.
Zooplankton Assemblages Related to Environmental Characteristics in Treeline Ponds in Finnish Lapland (pp 289-298)
Zooplankton communities of 17 subarctic ponds with differing catchment areas and habitat types in northern Finland were surveyed during the open water season from June to August. Ponds were located along a gradient that changes from a mountain birch woodland to a treeless tundra. In all sites, cladoceran abundance dominated that of copepods although there was a consistent pattern of increasing relative abundance of copepods toward the most barren ponds. Species richness declined with increasing altitude but diversity remained constant. Zooplankton communities within the same habitat type were similar. Temporal variation in species abundance showed a coherent temperature driven pattern along the whole altitudinal transect.
Roles Played by Timing of Seedling Development and Host Identity in Determining Fitness of an Annual, Subarctic, Hemiparasitic Plant (pp 299-305)
Individually mapped plants of Euphrasia frigida, a hemiparasitic annual, were followed for one growing season at a subarctic site in northern Sweden. The strongest factor influencing seed-set was the date when the seedling stage ended, i.e., when plants produced their first noncotyledonous leaves, probably equaling date of attachment to a host. The advantage for early-developing plants was large even with just a 5-d difference in development. A positive effect was caused by presence of the perennial legume Astragalus alpinus, both on seedling development and plant performance, whereas the total cover of nonleguminous herbs or graminoids had no influence on the performance of E. frigida.
Microbiology and Vegetation of Micro-oases and Polar Desert, Haughton Impact Crater, Devon Island, Nunavut, Canada (pp 306-318)
The input of nutrients into arctic polar deserts, aided by some physical processes, can result in localized areas of high biological productivity - "micro-oases." We examined the vegetation cover, and microbial and nematode abundance in the polar desert and in 38 micro-oases at the Haughton impact crater, Devon Island, Arctic Canada. Our sites were split between the alluvial terraces along the banks of the Haughton River and the breccia deposits resulting from the asteroid or comet impact 22 Myr ago that flank the alluvial terraces. The alluvial terraces have a vegetation cover that ranges from 2 to 11% depending on substrate and water availability with a species richness of 5 in most locations. The vegetation cover on the breccia is much lower, between 0.02 and 3% depending on water availability. The micro-oases on both substrates support between 2 and 98% cover, but they are smaller and more sparsely distributed than similar features found in the Truelove Lowland, Devon Island, and on Bathurst Island. Microbial and nematode numbers were an order of magnitude greater inside the micro-oases compared to outside. Micro-oases are often dominated by a particular species, resulting in well-defined groups of micro-oases that were separated by TWINSPAN analysis. The micro-oases at Haughton Crater provide insights into the process of colonization of a substrate resulting from an asteroid or comet impact and the unique biological characteristics of such substrates.
Characteristics and Growth of a Snowdrift in Arctic Alaska, U.S.A. (pp 319-329)
In arctic Alaska, 15% of the total winter snowpack is contained in large drifts. Stratigraphic sections reveal that these can form during as few as five weather events during winter, while comparison of stratigraphy and weather records show that significant deposition (up to 43% of the total drift volume) can occur during a single event of short duration (<72 h). Based on three years of wind, snowfall, and snow transport records, a set of rules was developed for predicting when periods of drift growth would occur. The rules were: 10-m wind speed >5.3 m s-1 for at least 3 h, wind direction within 30° of the normal to drift trap axis, and recent snowfall available for transport. When used, these rules successfully identified all drift-growth events, plus a few "extra" events that did not contribute substantially to drift growth. The extra events were invariably periods when there was sufficient wind to move snow, but insufficient snow for transport. In arctic Alaska drift size currently appears to be limited by precipitation rather than wind, leading us to speculate that an increase in precipitation could increase drift size and intensify the ecological, hydrological, and climatic impact of drifts on this arctic system.
Experimental Evaluation of Shading Effects in Seasonal Dynamics of Four Alpine Communities in Northwestern Caucasus, Russia (pp 330-339)
Light plays a significant role in determining composition of alpine communities. A series of 3-yr experiments to assess four alpine communities' responses to a severe reduction in insolation regime (95% reduction for the whole, first, or second half of the growing season) were carried out on Mount Malaya Khatipara, Karachaevo-Cherkessia Republic, northwestern Caucasus, Russia. The snowbed community developing under the deepest snow had the highest proportion of shade-tolerant species among the four communities. In contrast, the alpine lichen heath developing under little, or no snow accumulation was the most susceptible to shading. The heath lost over 70% of species after 3 yr of the all-season shading. The intermediate grassland and meadow lost ca. 50%, while the snowbed lost only 18%. Members of Cyperaceae family and evergreens Vaccinium vitis-idaea and Gentiana pyrenaica were the most shade-tolerant species, while most other species showed little tolerance of shading, particularly when shaded for the whole growing season. Two ephemeroid species increased their shoot numbers when shaded during the second half of the growing season. Generative shoots of all species showed greater relative decrease than the vegetative shoots of the same species. Snowbed species showed the most varied response. This is consistent with earlier findings of opportunistic character of snowbed flora. The snowbed species will be most adaptable to any possible future shifts in vegetation composition under climate change.
Restoration of an Alpine Disturbance: Differential Success of Species in Turf Transplants, Colorado, U.S.A. (pp 340-347)
Evaluating techniques for restoring alpine environments is important due to increasing human impacts on Colorado mountains. We studied restoration success after 1 yr on an alpine area disturbed by trampling at 3700 m a.s.l., Humboldt Peak, Sangre de Cristo Mountains, Colorado. This area was revegetated in summer 1997 by transplanting pieces of turf cut from a new trail. For both transplants and controls, 100 points were sampled in seventeen 70 × 70 cm plots. Vascular plant species richness did not differ between transplant and control plots. Thirty-one species showed absolute covers not significantly different between transplant and control plots, and twelve species had higher covers in control plots or showed a strong trend in that direction. Sums of covers of all species declined by 35% in transplant plots. Transplant and control plots had differential relative success of some important species as measured by relative cover although almost all differences were small. Grasses increased moderately and forbs declined by 9%. Relative cover of the dominant, Geum rossii, as well as two common graminoids, Carex phaeocephala and Trisetum spicatum, decreased in transplant plots. The forbs Polygonum bistortoides and Potentilla subjuga increased in relative cover in transplant plots, and one of the dominant species, Carex elynoides, as well as many secondary species, were not different between treatments. Success in total cover and of almost all species after 1 yr indicates turf-transplants work well in this community and should be employed to restore other damaged alpine areas when feasible.
Recovery in Alpine Heath and Grassland Following Burning and Grazing, Eastern Central Plateau, Tasmania, Australia (pp 348-356)
Long-term data from six sites in treeless subalpine and alpine vegetation in central Tasmania are used to document change in vegetation cover and life form dominance over time. All sites have been disturbed by burning and domestic stock grazing in the past. Although burning ceased at least 8 yr before initial measurements were taken, stock grazing still occurs at one site, and rabbits and native vertebrate herbivores (mainly wallabies) graze throughout the region. Vegetation cover increased across all sites over a 5- to 23-yr period at an average annual increment of approximately 1%. There was no significant relationship between the initial cover of bare ground and change in bare ground over time for most of the sites. Annual increases in vegetation cover were least in locations grazed by rabbits and native vertebrate herbivores and where domestic stock still grazed. Exclosures grazed only by rabbits had an intermediate rate of increase. Vegetation cover was found to increase most in ungrazed exclosures. The rates of increase in vegetation cover suggest that, in the absence of fire, it is a matter of decades before cover will be almost complete in the area.
Vegetation Change and Ecological Processes in Alpine and Subalpine Sphagnum Bogs of the Bogong High Plains, Victoria, Australia (pp 357-368)
Sphagnum bogs that were monitored over a 15-yr period showed significant changes in the abundance of diagnostic species. At plots ungrazed by cattle, the major bog species Sphagnum cristatum, Caltha introloba, and Carex gaudichaudiana increased significantly in cover. No such increases occurred in grazed plots. There were few changes in cover of the main structural vegetation types - closed heathland, low open heathland, and open herbfield on stony pavements. Sphagnum and the main herbfield species, Oreobolus pumilio and Caltha introloba, were dislodged and shifted over unvegetated stony pavements by snowmelt runoff, snowpack movement and cattle trampling. Experiments using Sphagnum transplants showed this species capable of colonizing pavements by establishing on other plants. Survival and growth of transplants were significantly greater on low compared with high water flow (high energy) sites. Grazing and trampling by cattle significantly reduced survival of transplants, thus disrupting the colonization of pavements; firstly, by directly reducing the survival and growth of Sphagnum and other colonists; and secondly, by preventing the formation of barriers to water flow that would facilitate colonization. We propose a successional dynamic based on some of the processes operating in the open herbfield and stony pavements of Sphagnum bogs.
Recent Forest Encroachment into Subalpine Grasslands near Mount Hotham, Victoria, Australia (pp 369-382)
Establishment of forest trees into subalpine grasslands near Mt. Hotham, southeast Australia, was quantified in 1998 across long-established forest-grassland boundaries in belt transects at four sites. Although the grasslands varied in their dominant species and groundlayer biomass, tree encroachment (principally by Eucalyptus pauciflora) occurred at all sites. Tree encroachment is a recent and synchronous event; all invading saplings were #31 yr old and the majority (54%) established between 1991 and 1995. Most sapling establishment (66%) occurred within 5 m of the forest-grassland boundary where the number of plants present was positively associated with the amount of overhanging tree cover at three of the four sites. No correlation between encroachment and groundcover type or biomass, however, was found at any site. Some of the recently established plants are now small trees (1-8 m in height) and have become reproductive, indicating that establishment in grasslands is successful, making ecotone shifts possible. Any changes in boundary position, however, will be slow given the limited distance that trees established from the forest edge. Tree encroachment near Mt. Hotham is likely the outcome of small-scale (e.g., regeneration microsite) and landscape-scale (e.g., climate, grazing) processes that require further clarification.