Absence Of Vegetation Research Articles

Sedimentation in a blast-zone lake at Mount St. Helens, Washington—Implications for varve formation

Sediment collected in traps in a newly formed lake in the blast-impact area at Mount St. Helens recorded a sediment yield that is about two orders of magnitude greater than for comparable basins with vegetation and similar precipitation. Most sediment was mobilized by storms and runoff at the onset of the wet season. The sedimentation response to strongly seasonal precipitation, in the absence of vegetation, produced turbidites and graded annual couplets. The style of sedimentation suggests an alternate mechanism for the formation of long sequences of graded clastic varves.

Preserved stable isotopic signature of subaerial diagenesis in the 1.2-b.y. Mescal Limestone, central Arizona: Implications for the timing and development of a terrestrial plant cover

A Precambrian exposure surface in the 1.2-b.y. Mescal Limestone has been isotopically examined for indications of a carbon isotopic signature that might indicate the presence of a subaerial vegetative cover in the middle Proterozoic. δ 18 O values of the Mescal carbonates show two distinct data sets: (1) dolomites from an unaltered zone which were unaffected by sub-aerial diagenesis having δ 18 O values ranging from +19.9 to +25.6‰ Standard Mean Ocean Water (SMOW) with cherts averaging +30‰, and (2) dolomites from a dissolution zone subaerially exposed in the Precambrian with δ 18 O values ranging from +13.9 to +22.4‰ and cherts averaging +25‰. δ 13 C of dolomite ranges from +3.7‰ Pee Dee Belemnite (PDB) in the unaltered zone to 0‰ in the dissolution zone. The dissolution zone consists of a karst breccia of recemented dolomite and chert fragments with numerous clastic solution dikes. Isotopic and field data indicate that the δ 18 O of the unaltered dolomite was fixed during early meteoric-water diagenesis, including dissolution-silicification of evaporites and dolomitization. During a later subaerial exposure event, a large flux of meteoric water flushed through the dissolution zone and produced the same isotopic patterns that Allan and Matthews documented for younger examples as indicative of a vegetatively covered land surface. Alternative explanations for producing the observed δ 13 C variations in the absence of vegetation do not seem feasible. We therefore suggest that the subaerial environment 1.2 b.y. ago was a biologically active zone.

Predation by Tiger Muskellunge on Bluegill: Effects of Predator Experience, Vegetation, and Prey Density

Many pellet-reared tiger muskellunge (F1 hybrid of female muskellunge Esox masquinongy and male northern pike E. lucius) do not survive stocking in reservoirs dominated by bluegill Lepomis macrochirus prey. Poor survival may occur because few hybrids capture bluegills. In a previous study done in hatchery ponds, only 10% of naive hybrids (those never before exposed to live prey) captured bluegills during 15 days. In similar ponds, we tested the effects of predator experience (using hybrids previously exposed to bluegill prey), vegetative cover, and bluegill density on the number of hybrids capturing prey. Few experienced or naive hybrids captured bluegills at low prey density, regardless of the presence or absence of vegetation. When bluegill density was increased from 1 to 5 prey/m2 in ponds or to 40/m2 in aquaria, many hybrids captured bluegills. Our pond study suggests that most hybrids will not fare well when stocked in lakes where only bluegill forage is present. Received April 19, 1983 Accepted May 21, 1984

Megalocypris ingens Delorme (Ostracoda) in Saskatchewan saline lakes: osmoregulation and abundance

Results of freezing point depression determinations show that the haemolymph of the ostracod, Megalocypris ingens Delorme, remains hyperosmotic to the medium as the concentration of the medium increases. Even though M. ingens is poikilosmotic, the median lethal concentration (LC50) for this species exceeds the LC50 for an insect species living in the same lakes that is capable of hyposmotic regulation. The LC50 for M. ingens occurred in sulphate-saline lake water with a specific conductance of 48 000 µS cm-1 (at 25 °C). The absence of vegetation may be more important than salinity in limiting the distribution of M. ingens in Saskatchewan saline lakes.

Diversity and Abundance of Spring Migratory Birds Using Habitat Islands on the Great Plains

-Relationships of area with numbers of species and individuals of spring migrants were examined for 69 shelterbelts (forest islands) in eastern South Dakota. Total abundance and number of species were as highly correlated with area during spring migration as during the breeding season. The relationships of area with total abundance and number of species were highly similar between two years of study. Area was more important in determining abundance and number of species than either diversity of plant species or isolation of the islands. The dispersion of migrants among islands, indicated by the relationships of area with total abundance and species numbers, could have been a result of passive dispersal, selection for larger area, or behavioral interactions. Passive dispersal was unlikely because the isolation of an island had no significant influence on abundance or diversity. Also, the diversity and abundance of migrants were modified by habitat conditions (i.e., vegetation diversity), indicating that migrants select the forest islands they inhabit. Migrants may select large areas but they should then have increased with area at an increasing rate, but this did not occur. Dispersion among islands may be the best way for migrants to replenish their energy reserves when food is scarce. Two facts suggest that migrants may interact to disperse themselves relative to food. First, application of a model for interacting species provided increasingly better fits to ecological groups that increasingly confined their foraging within shelterbelts. Second, the density of birds was greater in smaller islands than in larger islands owing to species that did not feed solely within the islands. The density of birds that did feed primarily within the islands remained more or less constant with changing area. Shelterbelts consist of rows of trees and shrubs forming long and narrow island configurations. Shelterbelt plantings began largely in the mid-1930's under the auspices of the Shelterbelt Project and the Prairie State Forestry Project directed by the U.S. Forest Service, Department of Agriculture (Read 1958), in order to reduce wind erosion and protect homes and livestock on the Great Plains. These islands of planted trees supplied potential habitat for many species of woodland birds. The vegetation structure of a particular shelterbelt modifies the composition, diversity, and abundance of bird species using that shelterbelt during spring migration and the summer breeding season (Martin and Vohs 1978). A strong relationship between numbers of breeding bird species and island area has been found for many real and habitat island systems (MacArthur and Wilson 1963, 1967; Abbot 1974, Johnson 1975, Diamond and Mayr 1976, Galli et al. 1976). With the exception of a recent study by Willson and Carothers (1979) in Arizona, the influence of area on the number of transient bird species and individuals using habitat islands during migration has not been reported. I examine here the influence of area of shelterbelts in eastern South Dakota on the diversity, abundance, and ecological structure of transient bird communities during the spring migrations of 1976 and 1977. STUDY AREA AND METHODS The 69 shelterbelts examined in this study were scattered throughout South Dakota between its eastern border and the Missouri River. There is approximately one shelterbelt per 115 ha in this area of the state, representing 1.1% of the land area (Walker and Suedkamp 1977). These small forests represented true habitat islands, being isolated from one another by fields of natural and planted grasses. The floral diversity was low and included only 15 tree and 14 shrub species. The most common tree species were Siberian elm (Ulmus pumila), American elm (U. americana), green ash (Fraxinus pennsylvanica), and hackberry (Celtis occidentalis), while the most common shrubs were honeysuckle (Lonicera tatarica), lilac (Syringa vulgaris), American plum (Prunus americana), and chokecherry (Prunus virginiana). I quantified the structural complexity of the vegetation for each shelterbelt. Ground and canopy coverages were measured by noting the presence or absence of vegetation through an ocular tube (James and Shugart 1970). Density of understory vegetation was measured using a density board (Giles 1971). Readings were taken between each planted row at three locations in each belt. Measurement of percent slope, from a fixed distance, estimated vegetation height.

Seed input as a factor in the regeneration of strip-mine wastes in Saskatchewan

Seed traps were set out on the spoil banks created by strip-mine coal operations in southeastern Saskatchewan. A total of 2721 seeds (2387 seeds/m2) was collected in the 1st season of which 97% was comprised of forb seeds and 3% of grass caryopses; 4216 seeds (3798 seeds/m2) were trapped in the 2nd year. Kochia scoparia was the most abundant species. Adequate seed input is occurring in the area to provide a good vegetation cover. The general absence of vegetation on the wastes must therefore reflect subsequent removal and deterioration of the seeds.

Cyclicity and the facies model concept in fluvial deposits

ABSTRACT Since the fining-upward cycle model for meandering-river deposits was published in 1963, about a dozen facies models have been defined for rivers of varying sediment grain size, channel multiplicity and sinuosity. However, this suite of models is inadequate for the interpretation of many fluvial deposits because it does not incorporate the effects of a variety of outside-the-basin (allocyclic) sedimentary controls. The most important of these controls is tectonics, because differential movement between and source area, and changes in the rate of movement, can cause major changes in fluvial sedimentary environments. These changes give rise to fining- or coarsening-upward cyclic sequences which are superimposed on the cycles generated by within-basin (autocylic) mechanisms. Variations in climate can cause variations in sediment grain size and in depositional style as a result of alterations in weathering modes and discharge characteristics. These latter variations have been studied in hot arid, warm temperate and fluvioglacial regimes, but are poorly known in other climatic zones. As a result, many of our preconceptions about fluvial geomorphology and sedimentation may be inappropriate for other climatic conditions such as hot, humid environments. Channel morphology varies between four basic styles: braided, meandering, anastomosed and straight, but the sedimentological characteristics of intermediate morphological types have yet to be quantified. Many pre-Carboniferous rivers appear to have lacked clearly defined channels with cutbanks. The probable cause was low bank cohesion caused by an absence of land vegetation, a condition that cannot be modelled accurately from observations of modern rivers. The absence of vegetation would have favoured a flash-flood depositional process, which tends to generate sheet-like deposits rather than lenticular, channel-bound units. Sedimentological studies in modern rivers are beset by the problem of preservability, in that a river's long-term aggradation behaviour is commonly unclear. The problem is compounded by the fact that many studies have been carried out on rivers that are actively degrading. Cyclic sequences in fluvial sediments can be produced by a variety of mechanisms, and the interpretation of a given deposit solely in terms of a published facies model may be misleading. For most fluvial sequences it is necessary to adopt a multivariate basin analysis approach.

Downslope Soil Movement in a Colorado Alpine Region: Rates, Processes, and Climatic Significance

Soil-movement rates, processes, and land-forms were studied above timberline on the east slope of the Colorado Front Range. Maximum rates of downslope movement measured in sorted stripes, turf-banked lobes and terraces, and stone-banked lobes and terraces at nine experimental sites on Niwot Range ranged from 0.4 to 4.3 cm/yr. Rates of displacement were strongly influenced by differences in moisture availability and gradient, but were relatively unaffected by differences in soil texture and temperature. Movement is currently confined to the upper 50 cm of soil; columns of small cement rods placed in vertical drillholes showed no downslope displacement below this depth after four years of burial.Periodic measurements of downslope movement and frost heaving during the 1965-66 annual freeze-thaw cycle suggest that solifluction is a more effective process than frost creep in the saturated axial areas of turf-banked lobes in wet sites, but is less effective than frost creep at their edges. Potential frost creep at one experimental site exceeded theoretical values calculated from heave and slope measurements. Retrograde movement was larger than anticipated. At a site where frost creep is the dominant movement process, stone-banked lobes moved three times as rapidly as the finer-textured soil between them; at a site where shallow solifluction is important, stripes of coarse debris moved only half as rapidly as stripes of fine material.Turf-banked lobes and terraces are the result of intense solifluction beneath a cover of vegetation; they form where downslope movement is impeded, and are normally associated with a decrease in gradient such as occurs on concave lower slopes. The shape of the front (linear or lobate) is determined by the uniformity of moisture distribution parallel to the contour of the slope. At least two generations of turf-banked lobes and terraces occur in the Niwot Ridge area. Terraces with gentle, subdued fronts and patterned treads date from the late Pleistocene, and were used as camping and butchering areas by prehistoric man as long ago as 7,650 ± 190 radiocarbon years. Most bear an Altithermal soil: five dates for the soil range from 5,800 ± 125 to 5,300 ± 130 BP. Lobes and terraces with overhanging fronts and unpatterned treads postdate the Altithermal interval: radiocarbon and stratigraphic evidence suggest that they formed late in the Temple Lake Stade of Neoglaciation. The front of one small Neoglacial turf-banked lobe has advanced at an average rate of 0.19 cm/yr during the past 2,340 ± 130 radiocarbon years.Stone-banked lobes and terraces are caused by frost creep and are favored by an absence of vegetation; they commonly develop where moving sorted stripes or blockfields encounter a decrease in gradient. Sorting is partially inherited, but is accentuated as the lobe or terrace moves downslope. Stone-banked lobes and terraces in the Niwot Ridge area developed late in the Temple Lake Stade of Neoglaciation. A series of radiocarbon dates from the buried A horizon in one stone-banked terrace suggests that its front has advanced at an average rate of 0.34 cm/yr during the past 2,470 ± 110 radiocarbon years. Movement was slow during the Temple Lake-Arikaree* interstade (2,650 to 1,850 BP), a time of soil formation and intense cavernous weathering, and during the Arikaree glacial maximum, when lichen measurements show that the slope was covered with an insulating blanket of perennial snow. Disappearance of the snowbank led to an eight-fold increase in the rate of terrace advance between about 1,150 and 1,050 BP.The widespread occurrence of stone-banked lobes and terraces, sorted polygons, and sorted stripes on the treads of turf-banked lobes and terraces suggests a general decline in the availability of moisture and the effectiveness of solifluction since the end of the Middle Stade of Pinedale (Late Wisconsin) Glaciation. During the latest Pinedale and earliest Neoglacial ice advances frost creep replaced solifluction as the dominant movement process on many slopes. Neither process is particularly effective today, except in specialized microenvironments that are saturated with meltwater in the autumn.

Downslope Soil Movement in a Colorado Alpine Region: Rates, Processes, and Climatic Significance

Soil-movement rates, processes, and land-forms were studied above timberline on the east slope of the Colorado Front Range. Maximum rates of downslope movement measured in sorted stripes, turf-banked lobes and terraces, and stone-banked lobes and terraces at nine experimental sites on Niwot Range ranged from 0.4 to 4.3 cm/yr. Rates of displacement were strongly influenced by differences in moisture availability and gradient, but were relatively unaffected by differences in soil texture and temperature. Movement is currently confined to the upper 50 cm of soil; columns of small cement rods placed in vertical drillholes showed no downslope displacement below this depth after four years of burial.Periodic measurements of downslope movement and frost heaving during the 1965-66 annual freeze-thaw cycle suggest that solifluction is a more effective process than frost creep in the saturated axial areas of turf-banked lobes in wet sites, but is less effective than frost creep at their edges. Potential frost creep at one experimental site exceeded theoretical values calculated from heave and slope measurements. Retrograde movement was larger than anticipated. At a site where frost creep is the dominant movement process, stone-banked lobes moved three times as rapidly as the finer-textured soil between them; at a site where shallow solifluction is important, stripes of coarse debris moved only half as rapidly as stripes of fine material.Turf-banked lobes and terraces are the result of intense solifluction beneath a cover of vegetation; they form where downslope movement is impeded, and are normally associated with a decrease in gradient such as occurs on concave lower slopes. The shape of the front (linear or lobate) is determined by the uniformity of moisture distribution parallel to the contour of the slope. At least two generations of turf-banked lobes and terraces occur in the Niwot Ridge area. Terraces with gentle, subdued fronts and patterned treads date from the late Pleistocene, and were used as camping and butchering areas by prehistoric man as long ago as 7,650 ± 190 radiocarbon years. Most bear an Altithermal soil: five dates for the soil range from 5,800 ± 125 to 5,300 ± 130 BP. Lobes and terraces with overhanging fronts and unpatterned treads postdate the Altithermal interval: radiocarbon and stratigraphic evidence suggest that they formed late in the Temple Lake Stade of Neoglaciation. The front of one small Neoglacial turf-banked lobe has advanced at an average rate of 0.19 cm/yr during the past 2,340 ± 130 radiocarbon years.Stone-banked lobes and terraces are caused by frost creep and are favored by an absence of vegetation; they commonly develop where moving sorted stripes or blockfields encounter a decrease in gradient. Sorting is partially inherited, but is accentuated as the lobe or terrace moves downslope. Stone-banked lobes and terraces in the Niwot Ridge area developed late in the Temple Lake Stade of Neoglaciation. A series of radiocarbon dates from the buried A horizon in one stone-banked terrace suggests that its front has advanced at an average rate of 0.34 cm/yr during the past 2,470 ± 110 radiocarbon years. Movement was slow during the Temple Lake-Arikaree* interstade (2,650 to 1,850 BP), a time of soil formation and intense cavernous weathering, and during the Arikaree glacial maximum, when lichen measurements show that the slope was covered with an insulating blanket of perennial snow. Disappearance of the snowbank led to an eight-fold increase in the rate of terrace advance between about 1,150 and 1,050 BP.The widespread occurrence of stone-banked lobes and terraces, sorted polygons, and sorted stripes on the treads of turf-banked lobes and terraces suggests a general decline in the availability of moisture and the effectiveness of solifluction since the end of the Middle Stade of Pinedale (Late Wisconsin) Glaciation. During the latest Pinedale and earliest Neoglacial ice advances frost creep replaced solifluction as the dominant movement process on many slopes. Neither process is particularly effective today, except in specialized microenvironments that are saturated with meltwater in the autumn.

Hourly Air and Near-Surface Soil Temperatures at Resolute, N.W.T.

Since 1959 the Geographical Branch of the Canada Department of Mines and Technical Surveys has been pursuing a program of enquiry into problems of periglacial geomorphology at Resolute, N.W.T. (74°43'N., 95°59'W.). This area was considered suitable because it is in an active periglacial region, where geomorphological processes are reduced to as near a mechanical process as can be found in nature, since there is an almost complete absence of vegetation. The study of soil temperature in the active layer of permafrost has formed a significant part of the program. In the past freeze-thaw cycles have received special consideration as continued freezing and thawing of the mantle has been considered instrumental in its disintegration. The Resolute program also included the study of freeze-thaw cycles and in the course of this study temperature data were collected at five levels at 4-minute intervals during the period from October 1959 to September 1960 inclusive. In this paper hourly air and near-surface soil data are being analysed as a preliminary to a larger study to be published later. It is realized that a 1-year record does not provide a stable frequency distribution, but as no similar set of data exists for a high arctic area, it is presented here. ...

The Sandfell Laccolith and ‘Dome of Elevation’

. Introduction The eastern part of Iceland is built mainly of a great series of plateau basalts dipping at low angles to the west, and the structure is magnificently exhibited in the sides of the deep valleys and fjords which incise the 3000–4000-foot plateau. The traveller is impressed by the constancy of the almost flat-lying trap featuring, which persists in the region of the ‘stock’ intrusions to the south (Cargill et alii , 1928), so that Sandfell, a hill of light-coloured rock on the south side of Faskrudsfjord, at once attracts attention because the basalts are disposed at high angles in proximity to it—a circumstance which was noted by Thoroddsen (1906, pp. 268, 277). The hill is a splendid example of a laccolith similar in type to those of the Henry Mountains, Utah, and equally impressive in its exposure. The combination of conditions which made the intrusions of the Henry Mountains the type of their class is present here—approximately level strata, intense erosion, and absence of vegetation (Gilbert, 1877, p. 97). The main hindrance to the complete elucidation of the structure is the extensive screes—to which Sandfell owes its name. This paper is based upon field investigations made on four visits between 1914 and 1932. In the earlier stages of the work snow-drifts hid some of the higher parts, but there has been a marked amelioration of climate in latter years, and in August 1932 all the drifts had disappeared. The district is unmapped, and in 1928 the second author made

Big Game Shooting and Travel in South-East Africa

THERE is a great deal of interest to the zoologist and botanist in Mr. Findlay's book on his experiences as a hunter in Portuguese South-East Africa and in Zululand. The area visited by this sportsman in Portuguese East Africa was the country in the basin of the Pungwe River (to the north-west of Beira). His journeys in this direction extended northwards to the verge of the Cheringoma Forest, which is not many days' journey south of the Lower Zambesi. This country is very similar in appearance to the lowlands of British Central Africa, that is to say, it is quite tropical, and is without any aridity or absence of vegetation. The wild Hyphaene and date palms are excellently illustrated by the author's photographs, so also are the huge baobab trees. A very good idea of the woodland of these countries (a tangle of wild date palms, acacias, and timber trees of evergreen foliage) is given on p. 75. The Hyphaene (H. crinita) appears in many photographs, noteworthy among which are those on pp. 27, 38, and 106. The palms given on pp. 105, 107, and in one or two other illustrations are probably the Borassus flabellifer; like so many other palms of this group, they have a bulge in the central portion of their lofty stem. A fine specimen of a baobab tree is given on p. 83. Big Game Shooting and Travel in South-East Africa. By F. R. N. Findlay. Pp. xii + 313. (London: T. Fisher Unwin, 1903.) Price 15s. net.