Showing papers on "Tundra published in 1995"
TL;DR: In this article, the authors manipulated light, temperature, and nutrients in moist tussock tundra near Toolik Lake, Alaska to determine how global changes in these parameters might affect community and ecosystem processes.
Abstract: We manipulated light, temperature, and nutrients in moist tussock tundra near Toolik Lake, Alaska to determine how global changes in these parameters might affect community and ecosystem processes. Some of these manipulations altered nutrient availability, growth—form composition, net primary production, and species richness in less than a decade, indicating that arctic vegetation at this site is sensitive to climatic change. In general, short—term (3—yr) responses were poor predictors of longer term (9—yr) changes in community composition. The longer term responses showed closer correspondence to patterns of vegetation distribution along environmental gradients. Nitrogen and phosphorus availability tended to increase in response to elevated temperature, reflecting increased mineralization, and in response to light attenuation, reflecting reduced nutrient uptake by vegetation. Nutrient addition increased biomass and production of deciduous shrubs but reduced growth of evergreen shrubs and nonvascular plants. Light attenuation reduced biomass of all growth forms. Elevated temperature enhanced shrub production but reduced production of nonvascular plants. These contrasting responses to temperature increase and to nutrient addition by different growth forms "canceled out" at the ecosystem level, buffering changes in ecosystem characteristics such as biomass, production, and nutrient uptake. The major effect of elevated temperature was to speed plant response to changes in soil resources and, in the long term (9 yr), to increase nutrient availability through changes in N mineralization. Species within a growth form were similar to one another in their responses to changes in resources (light or nutrients) but showed no consistent response to evelated temperature. Species richness was reduced 30—50% by temperature and nutrient treatments, due to loss of less abundant species. Declines in diversity occurred disproportionately in forbs, which are important for animal nutrition, and in mosses, which maintain soil thermal regime. There was no increased abundance of initially rare species in response to any treatment. During our 9—yr study (the warmest decade on record in the region), biomass of one dominant tundra species unexpectedly changed in control plots in the direction predicted by our experiments and by Holocene pollen records. This suggests that regional climatic warming may already be altering the species composition of Alaskan arctic tundra.
1,444 citations
TL;DR: Results indicate that mammalian grazers have a sufficiently large effect on vegetation and soil moisture that their extinction could have contributed substantially to the shift from predominance of steppe to tundra at the Pleistocene-Holocene boundary.
Abstract: A simulation model, recent experiments, and the literature provide consistent evidence that megafauna extinctions caused by human hunting could have played as great a role as climate in shifting fr...
405 citations
300 citations
TL;DR: The composition of the plant community was a greater control on CH 4 flux from the site than either water table height or CH4 production rates, indicating the importance of species-specific plant dynamics in controlling CH4 flux from arctic wetlands.
Abstract: The roles of plant transport and CH4 production in controlling CH4 flux from wet meadow tundra communities were investigated. Plant transport was the dominant pathway of CH4 flux from this ecosystem. Most CH4 production (measured within situ anaerobic incubations) occurred well below the water table, and C supply (estimated by anaerobic CO2 production) was the best single predictor of CH4 production rates. Plant transport of CH4 was controlled both by CH4 supply and the plant species.Eriophorum angustifolium transported substantially more CH4 than didCarex aquatilis, due to differences in size and structure of the two species. The composition of the plant community was a greater control on CH4 flux from the site than either water table height (which varied only slightly) or CH4 production rates, indicating the importance of species-specific plant dynamics in controlling CH4 flux from arctic wetlands.
266 citations
TL;DR: In this article, the authors examined the biophysical and biogeochemical effects of boreal forests and tundra ecosystems on atmospheric processes, and showed that the boreal forest decreases land surface albedo in the winter, warms surface air temperatures at all times of the year, and increases latent heat flux and atmospheric moisture at all months of a year.
Abstract: The effects of terrestrial ecosystems on the climate system have received most attention in the tropics, where extensive deforestation and burning has altered atmospheric chemistry and land surface climatology. In this paper we examine the biophysical and biogeochemical effects of boreal forest and tundra ecosystems on atmospheric processes. Boreal forests and tundra have an important role in the global budgets of atmospheric CO2 and CH4. However, these biogeochemical interactions are climatically important only at long temporal scales, when terrestrial vegetation undergoes large geographic redistribution in response to climate change. In contrast, by masking the high albedo of snow and through the partitioning of net radiation into sensible and latent heat, boreal forests have a significant impact on the seasonal and annual climatology of much of the Northern Hemisphere. Experiments with the LSX land surface model and the GENESIS climate model show that the boreal forest decreases land surface albedo in the winter, warms surface air temperatures at all times of the year, and increases latent heat flux and atmospheric moisture at all times of the year compared to simulations in which the boreal forest is replaced with bare ground or tundra. These effects are greatest in arctic and sub-arctic regions, but extend to the tropics. This paper shows that land-atmosphere interactions are especially important in arctic and sub-arctic regions, resulting in a coupled system in which the geographic distribution of vegetation affects climate and vice versa. This coupling is most important over long time periods, when changes in the abundance and distribution of boreal forest and tundra ecosystems in response to climatic change influence climate through their carbon storage, albedo, and hydrologic feedbacks.
254 citations
01 Jan 1995
TL;DR: The authors showed that global warming, resulting from increased concentrations of greenhouse gases, may affect ecosystems in different ways and to various extents, and that Coral reefs, mangroves, the arctic tundra, and high mountain ecosystems are particularly vulnerable.
Abstract: Global warming, resulting from increased concentrations of greenhouse gases, may affect ecosystems in different ways and to various extents (Emanuel et al. 1985; Bolin et al. 1986; Solomon and Shugart 1993, etc.). Coral reefs, mangroves, the arctic tundra, and high mountain ecosystems are particularly vulnerable (Markham et al. 1993).
207 citations
TL;DR: In this article, the authors measured free amino acid concentrations in soils from four major ecosystem types in arctic Alaska and found that the dominant free amino acids in these soils were glycine, aspartic acid, glutamic acid, serine, and arginine.
Abstract: Concentrations of free amino acids were measured in soils from four major ecosystem types in arctic Alaska. Total free amino acid concentrations were several-fold higher than ammonium (the major form of inorganic nitrogen) in water extracts of soils. The dominant free amino acids in these soils were glycine, aspartic acid, glutamic acid, serine, and arginine. Concentrations of total amino acids ranged 5-fold across communities, being highest in tussock tundra and lowest in wet meadows. Incubation experiments indicate that the turnover of amino acids is rapid, which suggests high rates of gross nitrogen mineralization in these soils. The high concentrations and dynamic nature of soil free amino acids suggest that this nitrogen pool is a significant component of nitrogen cycling in these tundra ecosystems.
178 citations
TL;DR: Active layer changes after the 1968 forest-tundra fire at Inuvik, N.W.T., have been monitored from 1968 to 1993 at three burned and two unburned sites as mentioned in this paper.
Abstract: Active layer changes after the 1968 forest-tundra fire at Inuvik, N.W.T., have been monitored from 1968 to 1993 at three burned and two unburned sites. In addition, a burned site has been used for ...
174 citations
01 Jan 1995
TL;DR: In this paper, the arctic vegetation is treated as a special type of tundra, but this is an inadequate simplification, as the major common features of real tundras and alpine vegetation are the absence of trees, the short stature of plants, and the low annual mean temperature.
Abstract: High-altitude vegetation is often treated as a special type of tundra, but this is an inadequate simplification. The major common features of real tundra and “alpine vegetation” are the absence of trees, the short stature of plants, and the low annual mean temperature. Most other components of the alpine environment may differ substantially from arctic tundra environments (Table 1; Bilhngs 1973, 1979a). The term “alpine” is used here exclusively for the vegetation above the natural subalpine tree line. Often this boundary is unsharp and is fragmented over several hundred meters of altitude. Where an upper tree line is missing, as in many arid mountain regions, the approximate level of the tree hne in the nearest more humid mountains is taken as a rough guidehne. At the polar end of the alpine vegetation, there is no clear distinction between the arctic-alpine and the arctic-lowland flora. Depending on region, most arctic-alpine vegetation north of 65° to 70°N is possibly better included in the term arctic (similar climate and species composition).
168 citations
TL;DR: The results suggest that soil temperature increases of up to 1°C, which may occur by the end of the next century as an effect of a predicted 4°C rise in air temperature, have only small effects on total N mineralisation in the short term in arctic soils.
Abstract: Impacts of climate change were simulated in two contrasting European arctic ecosystems, a high arctic polar semi-desert and a subarctic dwarf shrub heath, by increasing temperature (using polythene tents), precipitation and soil nutrient (NPK) availability. The effects of these treatments and their interactions on plant litter decomposition and soil nutrient fluxes were assessed. Polythene tents increased air, litter and soil temperatures but reduced litter and soil moisture contents. At both sites, litter decomposition was significantly retarded in the tent treatments due probably to reduced litter moisture contents. The tent treatment had no effect on extractable soil N pools or net total N mineralisation at either site, although the treatment significantly reduced net seasonal nitrification values at the subarctic site. The additional precipitation treatment significantly increased litter decomposition at the dwarf shrub heath site and the net amount of N mineralised at the polar semi-desert site. Litter decomposition was increased, as was net N mineralisation, by the application of nutrients. The results suggest that soil temperature increases of up to 1°C, which may occur by the end of the next century as an effect of a predicted 4°C rise in air temperature, have only small effects on total N mineralisation in the short term in arctic soils.
160 citations
TL;DR: In this paper, it was shown that the larger heating over the boreal forest in the spring and summer, as contrasted with weaker heating over adjacent tundra, results in a preferred position of the polar front along the northern edge of the Boreal forest.
Abstract: The analysis presented in this paper suggests that the larger heating over the boreal forest in the spring and summer, as contrasted with weaker heating over the adjacent tundra, results in a preferred position of the polar front along the northern edge of the boreal forest. This positioning is well documented in the literature (see, for example, Bryson, 1966; Barry and Hare, 1974; Kreps and Barry, 1970). This heating results from the lower albedo of the boreal forest which is not compensated by an increase in transpiration, even with the larger leaf area index of the forest. The warmer temperatures are mixed upward by the deep boundary layer over the forest and mesoscale circulations which result from the patchiness of heating associated with the heterogeneous landscapes of the forest. Thus in contrast to previous assumptions in which the arctic front position in the summer determines the northern limit of the boreal tree line, our study suggests the boreal forest itself significantly influences the preferred position of the front. This conclusion reinforces the findings of Bonan et al. (1992) and Foley et al. (1994) on the important role of boreal forest-tundra interactions with climate.
TL;DR: In this paper, the authors report results from a transect of methane flux measurements across tundra environments in Siberia and the European Arctic during July and August 1994, concluding that the mesic tundras fluxes were lower than what would be expected based on data from similar environments in North America, and there are indications that these environments may be significant atmospheric methane consumers.
Abstract: This paper reports results from a transect of methane flux measurements across tundra environments in Siberia and the European Arctic during July and August 1994. Overall, mean CH4 emission was 2.3±0.7 mg m−2 day−1 for the mesic tundra sites and 46.8±5.9 for the wet habitats with large intersite variability. The general scale of emissions was somewhat low compared to assumptions made about them in global methane budgets and models. In particular, the mesic tundra fluxes were lower than what would be expected based on data from similar environments in North America, and there are indications that these environments may be significant atmospheric methane consumers. Consistent consumption rates in combination with the large expanse of dry/mesic tundra environments suggest that it may be necessary to incorporate a high-latitude soil sink term in global methane budgets. However, the wet tundra emissions found between 67° and 77°N in this study were consistently higher than recent findings in comparable environments at much lower latitudes (50°–55°N). High northern latitudes therefore represent a very important player in the global methane budget. When compared across both mesic and wet sites, methane emission increased with increasing soil organic content, soil temperature, and soil moisture. The relationship between soil temperature and methane flux at the wet sites alone was highly significant, and the flux also increased with increasing soil moisture and organic content. No correlations were found between flux and the measured environmental parameters at the mesic sites when treated separately.
TL;DR: In this paper, the authors determined patterns in net N mineralization and microbial N pools among three communities, Kobresia, Acomastylis, and Carex meadows, that span a topographic gradient, and related any patterns to soil microclimate differences among these communities.
Abstract: The alpine tundra of the Colorado Front Range supports a variety of plant communities whose distribution corresponds to their topographic position. Our objectives were to : (i) determine patterns in net N mineralization and microbial N pools among three communities, Kobresia, Acomastylis, and Carex meadows, that span a topographic gradient, and (ii) relate any patterns to soil microclimate differences among these communities. Average yearly net N mineralization rates, measured with an in situ core incubation technique, were 1.2 g N m -2 in 1991 and 1.0 g N m -2 in 1992. No differences were detected in yearly N mineralization rates among the three communities ; however, net nitrification and other soil properties were found to differ among communities. Net N mineralization rates and microbial N showed strong temporal variation, and this variation was related to different variables for each community. Seasonal variation in N mineralization was related to soil water and microbial N in Kobresia meadows, to soil temperature and microbial N in Acomastylis meadows, and to soil water and temperature in Carex meadows. Seasonal changes in microbial N were related to soil water in Kobresia and Acomastylis meadows. Large fluctuations in microbial N indicate that periodic losses from the microbial pool may be important to N availability in this alpine tundra site.
TL;DR: In this paper, the authors formulated a general model of ecosystem carbon fluxes by linking a process-based canopy photosynthesis model to the Rothamsted soil carbon model for biomes that are not significantly affected by water limitation.
Abstract: Carbon exchange by the terrestrial biosphere is thought to have changed since pre-industrial times in response to increasing concentrations of atmospheric CO 2 and variations (anomalies) in inter-annual air temperatures. However, the magnitude of this response, particularly that of various ecosystem types (biomes), is uncertain. Terrestrial carbon models can be used to estimate the direction and size of the terrestrial responses expected, providing that these models have a reasonable theoretical base. We formulated a general model of ecosystem carbon fluxes by linking a process-based canopy photosynthesis model to the Rothamsted soil carbon model for biomes that are not significantly affected by water limitation. The difference between net primary production (NPP) and heterotrophic soil respiration (R h ) represents net ecosystem production (NEP). The model includes (i) multiple compartments for carbon storage in vegetation and soil organic matter, (ii) the effects of seasonal changes in environmental parameters on annual NEP, and (iii) the effects of inter-annual temperature variations on annual NEP. Past, present and projected changes in atmospheric CO 2 concentration and surface air temperature (at different latitudes) were analysed for their effects on annual NEP in tundra, boreal forest and humid tropical forest biomes. In all three biomes, annual NEP was predicted to increase with CO 2 concentration but to decrease with warming. As CO 2 concentrations and temperatures rise, the positive carbon gains through increased NPP are often outweighed by losses through increased R h , particularly at high latitudes where global warming has been (and is expected to be) most severe. We calculated that, several times during the past 140 years, both the tundra and boreal forest biomes have switched between being carbon sources (annual NEP negative) and being carbon sinks (annual NEP positive). Most recently, significant warming at high latitudes during 1988 and 1990 caused the tundra and boreal forests to be net carbon sources. Humid tropical forests generally have been a carbon sink since 1960. These modelled responses of the various biomes are in agreement with other estimates from either field measurements or geochemical models. Under projected CO 2 and temperature increases, the tundra and boreal forests will emit increasingly more carbon to the atmosphere while the humid tropical forest will continue to store carbon. Our analyses also indicate that the relative increase in the seasonal amplitude of the accumulated NEP within a year is about 0.14 % year -1 for boreal forests and 0.23 % year -1 in the tundra between 1960 and 1990.
TL;DR: In the last interglaciation (substage 5e) as mentioned in this paper, the authors examined the effects of extreme orbital changes on regional climates and biome changes using a physiologically based model of global vegetation types.
TL;DR: The initial goal of the Arctic Flux Study is a regional estimate of the present and future movement of materials between the land, atmosphere and ocean in the Kuparuk River basin in northern Alaska.
Abstract: Journal Of Biogeography (1995) 22, 365-374 The Al‘CtlC FIUX StUClV: a regional view Of trace gas release G. WELLER*1, F. S. CHAPIN2, K. R. EVERETT,3, J. E. HOBBIE4, D. KANE5, W. C. OECHEL6, C. L. PING7, W. S. REEBURGH8, D. WALKER9, and J. WALSH10, ILAII Science Management Ofiice, Center for Global Change, University of Alaska Fairbanks, PO Box 757740, Fairbanks, AK 99775, U.S.A. 2Department of Integrative Biology, University of California Berkeley, Berkeley, CA 94720, U.S.A. 33610 Johnstown—Utica Rd., Johnstown, OH 43031, U.S.A. 4Ecosystem Center, Marine Biological Laboratory, 67 Water St., Woods Hole, MA 02543, U.S.A. 5Department of Civil Engineering, University of Alaska Fairbanks, PO Box 755900, Fairbanks, AK 99775, U.S.A. 6Biology Department, San Diego State University, San Diego, CA 92182-0001, U.S.A. 7Agriculture and Forestry Experimental Station, University of Alaska Fairbanks, 533 Fireweed, Palmer, AK 99645, U.S.A. 8Department of Geosciences, University of California Irvine, 205 Physical Sciences, Irvine, CA 92717-3100, U.S.A. 9Institute of Arctic and Alpine Research, University of Colorado, Campus Box 450, Boulder, CO 80309-0450, U.S.A. “Department of Atmospheric Sciences, University of Illinois, 105 S. Gregory Ave., Urbana, IL 6180], U.S.A. Abstract. Fluxes of trace gases from northern ecosystems represent a highly uncertain and potentially significant compo- nent of the arctic land——atmosphere system, especially in the context of greenhouse-induced climate change. The initial goal of the Arctic Flux Study (a part of NSF’s Arctic System Science Program)’ is a regional estimate of the present and future movement of materials between the land, atmosphere and ocean in the Kuparuk River basin in northern Alaska. We are measuring rates and controls of processes along a north~ south transect running from the marshy coastal plain to moun- tain valleys. Important vertical fluxes under study are the release of CO2 and CH4 from soils and water, lateral fluxes are surface water, nutrients, and organic matter. A hierarchy of measurements allow the rates and under- standing of processes to be scaled from plots to the landscape, regional, and circumarctic level. These include gas flux mea- surements in small chambers, measurements over larger areas by eddy correlation from small towers, and measurements at the landscape scale from airplane overflights. Experimental manipulations of carbon dioxide, soil moisture, nutrients and soil temperature from this and other studies give information on process controls. The distribution of plant communities has been described at several landscape-scale sites and a hier- archic GIS has been developed for the region at three scales (plot, landscape, region). Climate is measured at six sites and hydrological processes are being studied at each watershed scale. In the soils, measurements are being made of soil organic matter and active layer thickness and of availability of soil organic matter for microbial transformation into CO2 and CH4. Fluxes and process understanding have been incorporated into a hierarchy of models at different scales. These include models of regional climate nested in a GCM; of regional- and continental-scale plant productivity and carbon cycling includ- ing CO2 release under altered climates; watershed and regional models of hydrology; and surface energy budgets. After the first year of study the regional climate model has been successfully configured to the northern Alaska region. We have also measured a large release of carbon dioxide from tundra soils in all but the coldest and wettest parts of the transect. The rates from eddy correlation towers (landscape level) agree closely with rates from chambers (plot level). Observations, experimental manipulations and modelling analyses result in the prediction that the combination of warmer and drier soils is responsible for the large CO2 release. Key words. Arctic, tundra ecosystem, global warming, car- bon dioxide, methane, trace gases, modelling. INTRODUCTION Greenhouse warming in northern land areas is predicted by global climate models to be several times greater than the global mean of 1.5—4.5°C (IPCC, 1992). During the past *Corresponding author. © 1995 Blackwell Science Ltd. several decades, the observed warming has been much stronger over the northern land areas than over the Arctic Ocean (Kahl et al., 1993) or subpolar oceans (Chapman & Walsh, 1993). The warming has been particularly large over Siberia, north western Canada and much of Alaska, where warming rates over the past 30 years are approxi- 365
TL;DR: In this paper, the spectral properties of the normalized difference vegetation index (NDVI) on three glacial surfaces of different ages in the vicinity of Toolik Lake, Alaska, were examined.
Abstract: The patterns of the normalized difference vegetation index (NDVI) on three glacial surfaces of different ages in the vicinity of Toolik Lake, Alaska, were examined. NDVI was derived from SPOT multispectral digital data, and the images were stratified according to boundaries on glacial geology and vegetation maps. Ground-level measurements of NDVI from common vegetation types were also collected, using a portable spectrometer. Late Pleistocene glacial surfaces have lower image-NDVI than older Middle Pleistocene surfaces, and the mean NDVI is correlated with approximate time since deglaciation. The trends are related to differences in NDVI associated with vegetation growing on mineral vs peaty substrates. Nonacidic mineral substrates are more common on the younger landscapes, and acidic peaty soils are more common on the older surfaces. The field-NDVIs of acidic dry, moist, and wet tundra are consistently higher than those of corresponding nonacidic tundra types. These same trends are seen when the SPOT NDVI image is stratified according to vegetation boundaries appearing on two detailed vegetation maps in the region. Above-ground biomass of moist and wet acidic tundra is significantly greater than corresponding nonacidic types. Vegetation species composition was examined along two transects on the oldest and youngest glacial surfaces. Shrub cover is the most important factor affecting the spectral signatures and biomass. Older surfaces have greater cover of shrub-rich tussock tundra and shrub-filled water tracks, and the younger surfaces have more dry, well-drained sites with low biomass and relatively barren nonsorted circles and stripes. These trends are related to paludification and modification of the terrain by geomorphic and geochemical processes. Similar patterns of spectral reflectance have been noted in association with a variety of large-scale natural disturbances in northern Alaska. However, extrapolation of these results to much broader regions of the circumpolar Arctic will require the use of sensors covering larger areas, such as the AVHRR aboard the NOAA satellites.
TL;DR: Pollen analysis of sediment cores from Grandfather and Ongivinuk Lakes reveals a record of postglacial vegetation and climate change in the northern Bristol Bay region as mentioned in this paper, where Betula shrubs probably first appeared in the region 11,300-11,300 yr B.P. and were restricted to favorable microhabitats until 9,800-9,800 yr B., but were relatively low Betula pollen abundance in these records compared to other areas of eastern Beringia.
TL;DR: In this article, a model of permafrost thermodynamics and methane emission has been developed for inclusion in the UK Meteorological Office land surface scheme, which was tested by driving it directly with surface meteorological observations and comparing the simulated methane emission to those observed during a field study on the North Slope of Alaska.
Abstract: Methane is an important greenhouse gas contributing approximately 15% to the present greenhouse warming. Tundra ecosystems between 50°N and 70°N are estimated to contain 14% of the global soil carbon and account for between 20 and 25% of the natural methane emissions. Consequently, enhanced anaerobic decomposition of tundra soil carbon and the associated increase in methane production could provide a significant positive feedback on the anthropogenic greenhouse effect. This work is an attempt to quantify this feedback for arctic tundra. A model of permafrost thermodynamics and methane emission has been developed for inclusion in the UK Meteorological Office land surface scheme. This improved scheme was tested by driving it directly with surface meteorological observations and comparing the simulated methane emission to those observed during a field study on the North Slope of Alaska. Results are also presented from simulations carried out with the single column version of the Hadley Centre climate model, for both current conditions and a simple doubled carbon dioxide warming scenario. The latter shows a significantly enhanced methane emission. In order to assess the dependence of this result on the particular scenario chosen, offline sensitivity studies were carried out using meteorological observations and a range of perturbations to air temperature and rainfall. DOI: 10.1034/j.1600-0889.47.issue3.2.x
TL;DR: Assessment of the environmental controls on FTE tree regeneration, whether the ecotone might be relictual, and whether tree invasion of nonforested FTE areas is occurring, measured tree regeneration in various environments within the FTE of Rocky Mountain National Park, Colorado.
Abstract: Ecotone vegetation may be especially sensitive to climate change. In particular, the invasion of subalpine meadows by tree seedlings has been well documented. However, there has been no systematic analysis of tree regeneration across the environmental heterogeneity of the alpine forest–tundra ecotone (FTE). Also, the position of the FTE may be relictual from more favorable climates of the past and therefore unresponsive to changing climate. To assess the environmental controls on FTE tree regeneration, to determine whether the ecotone might be relictual, and to determine whether tree invasion of nonforested FTE areas is occurring, we measured tree regeneration in various environments within the FTE of Rocky Mountain National Park, Colorado. Generally, seedling establishment appears to be controlled by patterns of soil moisture. Little seedling establishment was observed in krummholz openings, except for high seedling densities in willow wetlands. Tree seedling invasion of tundra is rare. Therefore, the up...
TL;DR: In this article, the authors used GIS and multivariate statistics to identify the major variants of forest-tundra ecotone, and identify the influence of the environment and natural disturbances on variation in the landscape structure of the ecology.
Abstract: Landscapes in the ecotone between forest and tundra contain a mosaic of patches of trees, meadows, lakes, disturbed areas, and other features. The structure of this mosaic affects species habitat and potential ecotone response to global change. However, the alpine forest-tundra ecotone may be insensitive to climatic change if it is a climatic relict or is frequently disturbed. We used GIS and multivariate statistics to (1) analyze landscape structure in transects across the ecotone in Rocky Mountain National Park, (2) identify the major variants of forest-tundra ecotone, and (3) identify the influence of the environment and natural disturbances on variation in the landscape structure of the ecotone. There are six major types of ecotone varying in the amount of natural disturbances, permanent features (e.g., lakes), closed forest, patch forest, and krummholz. Variation is primarily related to slope, elevation, aspect, and geology associated with the morphology of the mountains and the disturbances they pro...
TL;DR: The authors measured tree seedling and krummholz leader growth in various environments within the alpine forest-tundra ecotone of Rocky Mountain National Park to assess the potential pattern of response to tree seedlings.
Abstract: We measured tree seedling and krummholz leader growth in various environments within the alpine forest-tundra ecotone of Rocky Mountain National Park to assess the potential pattern of response to ...
01 Jan 1995
TL;DR: In this article, the authors focus on the role of ecosystems as exchange surfaces between atmosphere and vegetation and between vegetation and groundwater, and emphasize the importance of ecosystems for carbon exchange surfaces.
Abstract: Recently, attention among scientists has been focused on potential global climate change as well as on the deposition of pollutants and their impacts These perspectives emphasize the role of ecosystems as exchange surfaces between atmosphere and vegetation and between vegetation and groundwater (Dickenson 1988; Bolin 1988; Ulrich 1987) Particularly with respect to northern taiga and tundra regions, it is important to determine whether climate change may have already altered or may in the future alter rates (positive or negative) of ecosystem carbon storage (Oberbauer et al 1992; Oechel and Billings 1992) Furthermore, it is important to understand environmental controls on carbon fluxes and carbon storage, because the gradients in soil temperature, water availability, and available light energy in the Arctic are large and these will strongly affect the integrated values of net carbon dioxide (Tenhunen et al 1992) and methane exchange (Whalen and Reeburgh 1988, 1990) in polar regions Even when viewed simplistically and at the regional scale, temporal and spatial variation in ecosystem material exchange characteristics must be considered when estimating carbon balances (Miller et al 1983) At smaller scales such as the watershed, temporal and spatial variation in ecosystem structure, species composition, physiology, and environmental conditions determine momentary net gas exchange rates, but also provide clues concerning the manner in which ecosystem properties may be shifted regionally in a future climate (Chapin et al 1992)
TL;DR: In this article, the authors found that the erection of a snow fence on upland tundra caused a significant change of the vegetation over 11 years and that the presence of the snow fence resulted in a warmer soil in winter and a moister and cooler soil in summer.
Abstract: The erection of a snow fence on upland tundra caused a significant change of the vegetation over 11 yr. Compared to nearby exposed tundra, the presence of the snow fence resulted in a warmer soil in winter and a moister and cooler soil in summer. Moisture-intolerant species such as Cetraria nivalis and C. cuculata disappeared completely or decreased in frequency, whereas the more moisture-tolerant species such as Vaccinium uliginosum and Arctostaphylos alpina increased in frequency or established at the site. In terms of climate, any change that promotes a greater winter snowfall, which is the case for warming scenarios in general circulation models, would initiate a relatively rapid change in species composition on upland tundra, particularly if accompanied by increased summer rainfall.
TL;DR: In general, all tracks, regardless of age, showed small increases in the depth of thaw beneath them, and tracks were generally depleted of carbon and to a lesser, but significant extent, of potassium and phosphorus.
Abstract: Examination of the effects of vehicle and pedestrian tracks of known age (13 or more years) and intensity of use (single to multiple passages) on vegetation, soil chemistry, soil arthropods, soil thaw characteristics, and small-scale hydrological changes showed clear and inter-related patterns. In general, all tracks, regardless of age, showed small increases in the depth of thaw beneath them (c. 2.8 cm). Tracks were generally depleted of carbon and to a lesser, but significant extent, of potassium and phosphorus. Slight increases in NO 3 , NH 4 , and calcium were noted. Magnesium and total nitrogen seemed unaffected. On all tracks which had suffered multiple passages vegetation cover was significantly reduced. In a few sites where single passages were recorded, cover increased through proliferation of the sedge, Kobresia myosuroides. Abundance of soil arthropods was significantly reduced on tracks, but the diversity was not. In most sites, soil moisture and over-ground water flow did not seem affected. Only in sedge meadows where compression from a single passage resulted in channelling of water, and where multiple passages removed vegetation and initiated gulley erosion, were effects serious.
Book•
01 Jan 1995
TL;DR: For example, Canada's Vegetation as discussed by the authors provides a comprehensive overview of tundra, forest-to-forest, boreal forest and mixed forest transition, prairie (steppe), Cordilleran environments in western North America, temperate deciduous forests, and wetlands.
Abstract: Canada's Vegetation includes comprehensive sections on tundra, forest-tundra, boreal forest and mixed forest transition, prairie (steppe), Cordilleran environments in western North America, temperate deciduous forests, and wetlands. An overview of each ecosystem is provided, and equivalent vegetation types throughout the world are reviewed and compared with those in Canada. The integration of data on climate, soil, and vegetation in a single volume makes this an invaluable reference tool. Canada's Vegetation is sure to become a standard textbook for those in the environmental sciences.
TL;DR: In this article, the short-term responses of tundra vegetation and soils to aeolian sand and dust emanating from anthropogenically-bared surfaces in the low-arctic region of northwestern Siberia are described.
Abstract: This paper describes the short-term responses of tundra vegetation and soils to aeolian sand and dust emanating from anthropogenically-bared surfaces in the low-arctic region of northwestern Siberia. Such surfaces, including roads and quarries, are increasing substantially each year as the region undergoes massive gas- and oil-producing development. Data are presented which emphasize the ‘cumulative’ impacts of corridor construction, namely those effects which are measurable laterally, at some distance from the actual surfaces of roads and quarries, four years after their creation. In particular, changes in plant communities are documented, in addition to the chemistry and macronutrient status of mineral soils and dominant vascular plants and mosses, respectively, as affected by road-dust.Dramatic changes in plant community composition and cover were evident up to 200 m downwind from a ‘typical’ sand quarry. Although a few species appeared to respond favourably to rapid sand deposition, the great majority that were beset with it have declined in status or disappeared altogether. The exceptions were those growth-forms having the ability to keep perennating buds at or above the surface of the deepening sand (e.g. Betula nana, Salix spp., and Polytrichum spp.). The most pronounced decreases recorded were among lichens, hepatics, Sphagnum spp., and pleurocarpous mosses. The decline in Sphagnum spp., which dominate the moss layer and contribute much of the hummock-hollow microtopography, is already having a profound impact on community structure by virtually eliminating surface heterogeneity.
TL;DR: This is the first detailed study of a non-cyclic collared lemming population and tundra voles at Pearce Point, Northwest Territories, Canada, where population growth could be prevented by poor food or by predation losses, and landscape patchiness may also help to prevent population growth.
Abstract: From 1987 to 1989 we monitored population changes during summer of the collared lemming (Dicrostonyx groenlandicus) and the tundra vole (Microtus oeconomus) at Pearce Point, Northwest Territories, Canada (69° 48′ N, 122° 40′ W). Populations on four study areas did not cycle but remained at low density (<3/ha) each year and continued at low numbers for the following 3 years (Reid et al. 1995). Lemming numbers often declined throghout the summer in spite of continous reproduction, and population recovery occurred overwinter. Heavy predation losses of radio-collared lemmings occurred each summer and this lemming population may be trapped in a predator-pit. Collared lemmings breed in winter and only because of winter population growth do these populations persist. Tundra vole numbers increased rapidly in most summers but usually declined overwinter. Tundra voles do not seem able to sustain winter reproduction in this extreme environment and this prevents them from reaching high density because of the short summer. Population growth in both these rodents could be prevented by poor food or by predation losses, and landscape patchiness may also help to prevent population growth. For lemmings we do not think that a shortage of shelter or intrinsic limitations could be restricting population increase at Pearce Point. This is the first detailed study of a non-cyclic collared lemming population.
TL;DR: In this article, the authors measured the summertime energy budgets of contiguous wetland tundra and forest near Churchill, Manitoba along the coast of Hudson Bay over a five year period, 1989-1993.
Abstract: Summertime energy budgets of contiguous wetland tundra and forest near Churchill, Manitoba along the coast of Hudson Bay were measured over a five year period, 1989–1993. An examination of differences in energy budgets between the two sites showed that net radiation was similar in all years. Soil heat flux was greater at the tundra site in most, but not all, years. However, sensible heat flux was always larger at the forest site and latent heat flux was always greater at the tundra site. Mean daily Bowen ratios at both sites were less than unity in all years. Average Bowen ratios for the five years were 0.45 for tundra and 0.66 for forest. Wind direction is used as an analogue for changing climatic conditions where onshore winds are cooler and moister than offshore winds. Sensible and latent heat fluxes at both sites varied significantly between onshore and offshore wind regimes. However, differences between onshore and offshore fluxes at the tundra site were larger than for the forest. Thus, Bow...
TL;DR: Effects of 1984 and 1985 winter seismic exploration on arctic tundra were evaluated at 104 sites on the coastal plain of northeastern Alaska in 1991 and plant cover increased between initial years and...
Abstract: Effects of 1984 and 1985 winter seismic exploration on arctic tundra were evaluated at 104 sites on the coastal plain of northeastern Alaska in 1991. Plant cover increased between initial years and 1991 at sites with low to moderate initial disturbance. All disturbed sites had species whose cover values remained lower than controls, especially nonvascular plants and evergreen shrubs. Graminoids were less affected by disturbance. At high initial levels of disturbance, impacts included (i) surface compression at moist sites, with replacement of shrubs and mosses by hydrophytic sedges and (ii) persistence of bare patches in drier sites and replacement of prostrate shrubs with grasses. Although recolonizing species were generally common in controls, forbs and graminoids not present in adjacent areas were recolonizing some highly disturbed sites. Active layers were deeper at 55% of sites but shallower at 6 highly disturbed sites, where dead sedge leaves insulated permafrost. Plant biomass and nutrient concentr...