Abstracts
Vol. 30, No. 2, May 1998
Association of Plant Distribution Patterns and Microenvironments on Patterned Ground in a Polar Desert, Devon Island, N.W.T., Canada (pp 97-107)
David G. Anderson and L. C. Bliss
In this study, we quantify the distribution patterns of vascular plant species among microsites (stony border, transition, and center) of sorted stone nets and stripes. We also monitored edaphic factors (frost heave, temperature, moisture, and texture) at three intensive sites to identify controls on plant distribution. Adult plants were more abundant in the transition microsite (73 and 77%) with its cryptogamic crust than random distribution would predict (transition cover 17 and 14%) at the noncrusted stone nets and stone stripes, respectively. Adult plants were frost heaved (10 and 32%) from the bare-soil center microsites at both sites. Nearly all of the few seedlings were in the transition microsite.
At the crusted stone net, three species were randomly distributed; five species were over-represented in the two border microsites and two species were underrepresented there. No plants were frost heaved at this site and seedlings were abundant. There were 7.3 plants per lineal meter at the crusted net and only 3.0 and 2.3 plants per lineal meter at the noncrusted stone stripes and stone nets, respectively.
Of the environmental factors measured, soil heave (measured as soil settlement) appears most influential. Surface soils (0-1 cm) dry between summer rains and this may inhibit seedling establishment some summers. Soils at depth (5-10 cm) remain near saturation. Soil temperatures differed little between microsites as did soil texture.
The Influence of Cryptogamic Crusts on the Thermal Environment and Temperature Relations of Plants in a High Arctic Polar Desert, Devon Island, N.W.T., Canada (pp 108-120)
Warren G. Gold
The thermal microenvironment and leaf temperatures of two plants (Saxifraga caespitosa and S. oppositifolia) were studied in a high arctic polar desert over four summers. Surface and plant temperatures exceeded air temperatures by 5 to 15°C during sunny periods, with smaller effects on soil temperature in plant rooting zones. Midday plant temperatures of 20 to 30°C measured during good weather are favorable for physiological activity, but the number of such days is restricted by a short snow-free period (16-45 d).
Surfaces in polar deserts are dominated by sorted stones and bare mineral soil with sparse vascular plant cover (usually <5%). Infrequent snowflush sites are scattered within this landscape, containing greater plant cover and a cryptogamic crust on the mineral soil surfaces. The potential role of this black crust in facilitating greater plant cover by enhancing the thermal relations of plants was investigated in this cold environment. Reduced albedo of crusted surfaces led to higher surface (8-12°C) and soil (4-5°C) temperatures than in noncrusted areas. However, adult plants did not differ in tissue temperature on cryptogamic and bare surfaces. Root growth and survival of seedlings, which were thermally coupled to the surface by their small mass, are more likely to be highly influenced by the presence of crusted surfaces in this high arctic polar desert ecosystem.
Nitrogen Uptake during Snowmelt by the Snow Buttercup, Ranunculus adoneus (pp 121-125)
R. B. Mullen, S. K. Schmidt, and C. H. Jaeger III
Seasonal patterns of nitrogen (N) uptake were measured to assess the ability of the alpine herb Ranunculus adoneus to utilize the flush of N during snowmelt in an alpine tundra ecosystem. Development of mycorrhizal and dark septate fungi were also monitored within the roots of this snowbed plant in order to determine the role of these fungi in N acquisition. In addition, soil temperature, moisture, and inorganic N levels were measured to determine possible influences of edaphic factors on plant N uptake. In contrast to P uptake, which occurs late in the growing season and corresponds with arbuscular mycorrhizal (AM) development, N uptake occurred very early in the growing season before new roots and active AM fungal structures were formed. Soils at this time were cold and wet and NH4+ was the predominant form of inorganic nitrogen. Our data indicate that R. adoneus is able to take advantage of the early season flush of N by utilizing the previous year's root system which is heavily infected with a dark septate fungus. Given the high density of R. adoneus plants (135 plants per m2) in this snowbed system, they are a significant sink (ca. 0.5 g N per m2) for nitrogen released from within or beneath the alpine snowpack.
Persistent Suppression in Dwarf Birch after Release from Heavy Summer Browsing by Caribou (pp 126-132)
Michel Crête and G. Jean Doucet
The Rivière George Caribou Herd (RGCH), in northern Québec, erupted during a few decades to culminate at approximately 800,000 animals by 1990. The RGCH appeared regulated by competition for summer forage. Repeated browsing and trampling reduced summer range productivity to 50% compared to ungrazed areas, lichens and dwarf birch having been mostly responsible for this reduction. A reconnaissance flight in 1991 and intensive field work the following two summers suggested that caribou use of dwarf birch leaves was light following the period of peak numbers. We hypothesized that birch stands would show signs of rapid and vigorous recovery in 1993-1994. We surveyed five heavily browsed birch stands, and two inaccessible, lightly browsed ones. Although utilization of birch leaves by caribou ranged between 0 and 6% during the 1994 growing season, heavily browsed stands exhibited no signs of rapid and strong recovery. Young plants did not abound in heavily browsed stands compared to lightly browsed ones, neither was wood accumulation faster in the former than in the latter. Stem density and height were similar in heavily browsed and lightly browsed stands. However, the leaf/wood ratio and the percent dry weight of leaves and wood were higher in lightly browsed than in heavily browsed stands, which resulted in approximately twice as high leaf biomass in lightly browsed than in heavily browsed stands. We hypothesized that previous intense caribou browsing caused a persistent suppression of dwarf birches, and that stems could not accumulate sufficient reserves during a growing season to deploy more leaves in the next spring in order to return the leaf/wood ratio to a normal value. We discuss the consequences of such a reaction of dwarf birch to herbivory on the demography of the RGCH.
Distribution, Community Structure, and Microhabitats of Soil Invertebrates along an Elevational Gradient in Taylor Valley, Antarctica (pp 133-141)
Laura E. Powers, Mengchi Ho, Diana W. Freckman, and Ross A. Virginia
Soils in the Antarctic Dry Valleys have been significantly influenced by soil formation factors such as parent material, climate, and topography. Factors common in more temperate zones, including chemical weathering and leaching of minerals, occur to a much lesser extent in these cold arid soils, leading to an accumulation of salts and bases, which will likely affect the distribution of soil biota. Since the intensity of these factors may vary with topography, this study examined the soil properties and soil invertebrate communities along an elevational gradient in Taylor Valley, Antarctica. We sampled from two spatial scales (1 ° 1 m and 10 ° 10 m) at three sites (83, 121, and 188 m a.s.l) on the south side of Lake Hoare in Taylor Valley, and examined soil moisture, nitrogen, carbon, pH, and electrical conductivity (which provides an estimation of soil salinity), as well as the distribution and community structure of soil invertebrates. We found significant differences in soil properties with elevation, along with associated differences in soil communities. Biodiversity was greatest at the lowest elevation, closest to the shore of Lake Hoare, where soil moisture, carbon, and nitrogen were highest, and salinity was lowest. Scottnema lindsayae dominated the nematode communities found at all sites. Electrical conductivity was higher and carbon and nitrogen contents were lower at the upper elevations. The distribution of both Eudorylaimus and Plectus appeared to be influenced by soil moisture; electrical conductivity affected the mortality of all three nematode genera found. Soil properties did differ with sampling scale, suggesting that changes in microhabitats not detected at sampling intervals of a meter or more may be more reliably detected by sampling at a smaller scale.
Re-evaluation of Pre-Late Wisconsin Glacial Deposits, Lower Naknek River Valley, Southwestern Alaska, U.S.A. (pp 142-153)
Darrell S. Kaufman and Caleb H. Thompson
The lower Naknek River exposes thick (~20 m) successions of glaciogenic sediment of pre-late Wisconsin age on the northern Alaska Peninsula. The stratigraphy of the deposits, and the physical and mineralogical properties of diamicton beds, together with recently reported geochronological evidence, prompt a re-evaluation of the pre-late Wisconsin glacial history of the region. Three sites expose diamicton beds that can be separated from overlying units on the basis of geochronologic or sedimentologic criteria. These older diamicton beds predate formation of a last-interglacial marine-lag gravel at South Naknek beach. Data on younger diamicton units lack stratigraphic or geographic trends that indicate distinct tills related to separate ice advances. We therefore suggest that the regionally extensive surficial drift (from Pauls Creek, at the outer margin of the Mak Hill moraine, to the mouth of Naknek River) was deposited during a single glaciation. Lumping the drift into one unit is consistent with geochronological evidence indicating that ice from the Alaska Peninsula reached its maximum limit relatively recently, since the last interglaciation. We speculate that Johnston Hill, a prominent landform within the limits of this drift sheet, was formed by ice thrusting of proglacial sediment during the late Pleistocene. Previously it was interpreted as a conventional moraine and ascribed to a separate, climatically significant and regionally correlative glaciation of pre-late Pleistocene age.
Glacier Regimes, Periglacial Landforms, and Holocene Climate Change in the Kigluaik Mountains, Seward Peninsula, Alaska, U.S.A. (pp 154-155)
Parker E. Calkin, Darrell S. Kaufman, Bruce J. Przybyl, W. Brett Whitford, and Brian J. Peck
Three glaciers of the Kigluaik Mountains are very small and the only ones on the Seward Peninsula and surrounding west-central Alaska, but they are important climatically. They display the typical recession in response to recent warming, as well as moraine evidence of Little Ice Age worldwide cooling peaks of the 17th and 19th centuries. The terminal moraine of Grand Union glacier, dated lichenometrically at about A.D. 1645, indicates that equilibrium line altitudes fell about 170 m from present levels at this time, or one half the amount estimated locally for late Wisconsin glaciation. Periglacial landforms throughout the Kigluaik Mountains display ample evidence of the earlier Neoglacial cooling of the Holocene. Minimum (lichenometric) ages from active tongue-shaped rock glaciers and protalus ramparts, as well as maximum 14C ages for pingo development are compatible with a wide range of published proxy climate data indicative of middle to late Holocene cooling, particularly from about 4000 to 3000 yr ago. Increasing warmth of the late 20th century is showing its direct effects on Grand Union glacier, the only active glacier remaining in this transitional maritime-continental climatic regime of western Alaska. With an estimated net mass balance of °0.8 m water equivalent, it is, along with the other two stagnant glaciers of the Seward Peninsula, projected to disappear by about A.D. 2035.
Soils and Cryoturbation in Moist Nonacidic and Acidic Tundra in the Kuparuk River Basin, Arctic Alaska, U.S.A. (pp 166-174)
J. G. Bockheim, D. A. Walker, L. R. Everett, F. E. Nelson, N. I. Shiklomanov
We compared 22 pedons derived from silty materials in moist nonacidic tundra (MNT) and moist acidic tundra (MAT) in the arctic foothills of the 9200-km2 Kuparuk River basin in northern Alaska. Soils in MNT have thinner organic horizons, a significantly thicker active layer, and greater cryoturbation than soils in MAT. The quantities of clay and organic-plus-inorganic C in the upper 100 cm are comparable; however, soils in MNT have significantly greater amounts of extractable Ca, Mg, and sum of base cations and significantly lower amounts of exchangeable acidity and Al than soils in MAT. Tissues from forbs, sedges, and woody shrubs in MNT have two to three times as much Ca as the same or similar species in MAT. The area of nonsorted circles was significantly greater in MNT (9.6%) than in MAT (0.9%). Although the existence of nonacidic tundra in the Arctic has been known for some time, its origin and distribution have not been fully explained. Our data link soil and vegetation properties and indicate that cryoturbation plays an important role in maintaining MNT in arctic Alaska.
Frequency Distributions of Rhizocarpon geographicum s.l., Modeling, and Climate Variation in Tröllaskagi, Northern Iceland (pp 175-183)
Chris Caseldine and Andy Baker
Seven stable moraine surfaces in Tröllaskagi, northern Iceland, were sampled to produce frequency distributions of the sizes of up to 1000 Rhizocarpon geographicum s.l. thalli at each site. All frequency distributions showed a similar form, with patterns of disruption at the same points in the curves. In order to examine the possible cause(s) of this disruption, the structure of the observed distributions was compared with randomly generated distributions of lichen sizes. In the absence of snowpack data, temperature observations for the last 115 yr were used to produce duplicated model runs simulating the potential effects of snowkill on the lichen communities, producing results in close agreement with the observed data. It is concluded that in this area of northern Iceland, lichen growth was disrupted at four periods over the last 120 yr, and that at these periods possibly 80 to 100% of lichen thalli may have been lost. This has implications for lichenometric dating of moraines in the region, but as yet it is not possible to determine whether disruptions were solely due to climate, or to a combination of factors, including competition.
Effects of Rock Surface Temperature on Exfoliation, Rock Varnish, and Lichens on a Boulder in the Hunza Valley, Karakoram Mountains, Pakistan (pp 184-192)
Tetsuya Waragai
Granodiorite boulders on a moraine around the Batura Glacier in the Karakoram Mountains have exfoliation sheets and rock varnish on the south surface, and lichens and salt efflorescence on the north surface. To elucidate the formative conditions of these surface features, temperatures of a boulder at two points, one each on the north and south surfaces, were measured simultaneously with air temperature at 1-h intervals for 1 yr from July 1994 to July 1995. The annual temperature range of the south surface was 5°C higher than that of the north surface. The south surface had diurnal temperature ranges of 30°C with no seasonal change, while the north surface had diurnal ranges of 20°C in summer and 5°C in winter. Maximum heating and cooling rates of the south surface were high, being +12.6 and °14.5°C h-1, while those rates in the north surface were low at +6.5 and °7.7°C h-1, respectively. These results suggest that the difference in microclimatic conditions have affected the formation of rock surface features; for example, high rates of change in rock temperature on the south surface may produce exfoliation sheets.
Terminology and Predominant Processes Associated with the Formation of Weak Layers of Near-Surface Faceted Crystals in the Mountain Snowpack (pp 193-199)
Karl W. Birkeland
Although recent observations indicate that weak layers of near-surface faceted crystals are widely associated with snow avalanches, little research has addressed these layers. Further, current research has been hindered by an absence of a framework with which to discuss their formation. This paper proposes terminology and describes three predominant processes observed in mid-latitude mountains which result in extreme near-surface temperature gradients, thereby forming near-surface faceted crystals: radiation recrystallization, melt-layer recrystallization, and diurnal recrystallization. It is hoped that this framework will improve scientific discussion and theory-building related to the formation and spatial distribution of near-surface faceted crystals.
Near-Surface Faceted Crystals Formed by Diurnal Recrystallization: A Case Study of Weak Layer Formation in the Mountain Snowpack and Its Contribution to Snow Avalanches (pp 200-204)
Karl W. Birkeland, Ron F. Johnson, and D. Scott Schmidt
In the winter of 1995-96 we investigated the temperature and vapor pressure gradient conditions associated with the formation of faceted crystals that develop in the upper levels of the snowpack due to diurnal recrystallization. We used an array of six thermocouples connected to a datalogger to continuously measure snow temperatures in the region from 0.005 m above the snow surface to 0.20 m below the snow surface. Measurements during clear sky conditions in March showed temperature gradients in excess of 200°C m-1 at night in the top 0.05 m of the snowpack, with the temperature gradient shifting direction and exceeding 100°C m-1 through this layer during the day. These temperature gradients resulted in vapor pressure gradients which exceeded 25 mb m-1 during the day and at night. During this time, a significant weak layer of 1 mm faceted snow formed within 36 h. Widespread avalanche activity occurred for up to 9 d after this layer was buried by 0.50 m of snow.