Showing papers on "Tundra published in 1989"

Recent fire history of the northern quebec biomes

Abstract: The recent fire history of northern Quebec biomes (54 000 kM2), including the northern Boreal Forest, the southern and northern Forest-Tundra, and the Shrub Tundra, was documented by examining size and dates of 20th century wildfires using tree ring techniques. Results showed that pronounced south-north differences in fire properties existed, corresponding to climate and vegetation gradients. Fire frequency per biome de- creased south-north from closed forest (0.7 fire/yr) to Shrub Tundra (0.4 fire/yr). Average fire size decreased south-north by 100-fold from 8000 ha in the northern Boreal Forest to 80 ha in the Shrub Tundra, while modal fire size was 80%) of the northern Forest-Tundra and the Shrub Tundra were 100 000 ha occurred only in the northern Boreal Forest and the southern Forest- Tundra. Less than 35% of all mapped fires in the Boreal Forest were 30% were > 1000 ha. From south to north, the fire-free interval per biome was, respectively, 2.6, 0.6, 0.6, and 2.2 yr, the Boreal Forest data being overestimated. The largest burned areas were recorded in the 1 950s throughout the biomes, most likely associated with long- lasting drier and warmer conditions. The fire rotation period per biome, based on the percentage of burned areas during the 1920-1984 period (or 1930-1984 in Tundra), in- creased south-north by 100-fold from 100 yr in the northern Boreal Forest to 9320 yr in the Shrub Tundra. The fire rotation period around the tree line, i.e., 20 km south and north of the present tree line, was estimated to be > 7800 yr. Biome boundaries have developed and are maintained in response to fire by the ability of spruce to seed and regenerate. Stability of northernmost conifer sites is maintained by (1) the inability of patchy shrub and conifer cover in the northern Forest-Tundra and Shrub Tundra to carry fire and (2) failure of trees to produce viable seeds in these two biomes. Present data suggest that the area is characterized by a much higher fire frequency than expected from the fire weather index and from calculated frequencies typical of vegetation-type studies. It is concluded that size of the study area is a key element in the determination of regional fire regimes. Finally, the ecological significance of the natural fire rotation and postfire regeneration in northern environments is discussed in a paleoecological perspective.

The Cost of Tundra Plant Structures: Evaluation of Concepts and Currencies

Abstract: Carbon costs of synthesis are quite similar among parts and species of tundra plants and among chaparral shrubs, because all plant parts have substantial concentrations of certain energetically expensive constituents (either lignin or protein and tannin). I found no evidence to support the generalization that evergreen leaves are more expensive to produce than deciduous leaves. In contrast to carbon, initial nitrogen and phosphorus costs of synthesis differ substantially among plant parts and species. These costs are higher in leaves than in stems and tend to decrease from deciduous shrubs and forbs to graminoids to evergreen shrubs to mosses to lichens. Nutrient costs also vary substantially among species within a growth form. Final nitrogen and phosphorus costs are much less than initial costs because of resorption from senescing parts, whereas final carbon costs are not greatly modified by resorption. Carbon and nutrient costs are completely interconvertible, if their exchange ratios are known. However...

Terrain, vegetation and landscape evolution of the R4D research site, Brooks Range Foothills, Alaska

Abstract: Maps of the vegetation and terrain of a 22 km2 area centered on the Department of Energy (DOE) R4D (Response, Resistance. Resilience to and Recovery from Disturbance in Arctic Ecosystems) study site in the Southern Foothills Physiographic Province of Alaska were made using integrated geobotanical mapping procedures and a geographic-information system. Typical landforms and surface forms include hillslope water tracks, Sagavanirktok-age till deposits, nonsorted stone stripes, and colluvial-basin deposits. Thirty-two plant communities are described; the dominant vegetation (51% of the mapped area) is moist tussock-sedge, dwarf-shrub tundra dominated by Eriophorum vaginatum or Carex bigelowii. Much of the spatial variation in the mapped geobotanical characters reflects different-aged glaciated surfaces. Shannon-Wiener indices indicate that the more mature landscapes, represented by retransported hillslope deposits and basin colluvium, are less heterogeneous than newer landscapes such as surficial till deposits and floodplains. A typical toposequence on a mid-Pleistocene-age surface is discussed with respect to evolution of the landscape. Thick Sphagnum moss layers occur on lower hillslopes, and the patterns of moss-layer development, heat flux, active layer thickness, and ground-ice are seen as keys to developing thermokarst-susceptibility maps.

Differences in growth and nutrient use among arctic plant growth forms

Abstract: Deciduous species (graminoids, forbs and deciduous shrubs) completed accumulation of biomass, nitrogen (N) and phosphorus (P) in new leaves and current-year's twigs by midsummer in arctic Alaska, whereas these processes continued throughout the growing season in the same tissue of evergreen shrubs. Nand P-use-efficiency increased from deciduous species to evergreen shrubs to lichens and mosses. Fertilization with N-plus-P had no effect on N-use-efficiency in deciduous leaves but caused a decline in N-useefficiency in evergreen leaves, mosses and lichens. P-use-efficiency declined with nutrient addition in leaves of all growth forms. Approximately half of the maximum pools of leaf N and P were withdrawn from leaves prior to autumn senescence, but this resorption was unaffected by nutrient addition treatment or by growth form. Key-words: Arctic, deciduous, evergreen, growth, nitrogen, phosphorus, resorption, tundra

Irradiance and temperature effects on photosynthesis of tussock tundra Sphagnum mosses from the foothills of the Philip Smith Mountains, Alaska.

Abstract: Photosynthetic characteristics of three species of Sphagnum common in the foothills of the Brooks Range on the North Slope of Alaska were investigated. Generally, light-saturated rates of net photosynthesis decreased in the order S. squarrosum, S. angustifolium, and S. warnstorfii when plants were grown under common growth chamber conditions. For field-grown S. angustifolium, average light compensation point at 10°C was 37 μmol m-2s-1 photosynthetic photon flux density (PPFD), and light saturation occurred between 250 and 500 μmol m-2 s-1. At 20°C, compensation point increased to 127 μmol m-2s-1 and the PPFD required for light saturation increased to approximately 500 μmol m-2s-1, while maximum rates of CO2 uptake increased only slightly. Light response curves of chamber-grown plants exhibited substantially lower compensation points and higher light-saturated rates of CO2 assimilation than field-grown material, due perhaps to a higher percentage of green, photosynthetically competent tissue. All three species exhibited broad responses to temperature, with optima near 20°C, and maintained at least 75% of maximum assimilation between approx. 13° and 30°C. Rates at 5°C were approx. 50% of maximum. Studies of the microclimate of Sphagnum at the field research site suggest that CO2 uptake should occur at near light-saturated rates during the day in open tussock tundra but that PPFD may often be limiting under Salix and Betula canopies in a water track drainage. Simulations using a simple model provided a seasonal estimate of 0.78 g dry weight (DW) of S. angustifolium produced from each initial g of photosynthetic tissue under willow canopies, assuming no water limitations. Although the simulation model suggests that production would be 66% higher in open tussock tundra, S. angustifolium is rarely found in this potentially more stressful habitat. To explain the relative abundance of Sphagnum in shaded water track areas as compared to open tussock tundra, we postulate that the vascular plant canopies provide protection from adverse effects of high temperatures, excess irradiance and reduced water availability. Under conditions of normal water availability, removal of the vascular plant cover did not affect the tissue water content of S. squarrosum, but resulted in a strong decrease in photosynthetic capacity, accompanied by chlorophyll bleaching. These results suggest that photoinhibition may limit production under certain conditions.

Late-Quaternary History of High-Elevation Vegetation in the White Mountains of New Hampshire

Abstract: The pollen and plant—macrofossil records from four small lakes in the subalpine and alpine zone of the White Mountains, New Hampshire, give a 13 000—yr paleoenvironmental history. The White Mountains were deglaciated before 13 000 yr BP. Downwasting of the continental ice sheet was rapid. The summits projected above the ice as nunataks for only a brief period of time. Residual ice may have existed in Franconia Notch until 11 000 yr BP. From 13 000 to 11 750 yr BP a barren periglacial desert covered the highest altitudes in the White Mountains. Tundra vegetation occupied the lower slopes and valleys. The mean annual temperature was roughly 5°—10°C colder than today. Sparse tundra vegetation surrounded all four high—elevation sites from 11 750 to 10 300 yr ago and several taxa, particularly Artemisia and Caryophyllaceae, indicate disturbance. The summits were subjected to intense periglacial activity. The mean annual temperature was 4—6° lower than present. By 10 300 yr BP shrubs such as willow, juniper, an...

The Significance of the Date of Snow Disappearance on the Arctic Tundra as a Possible Indicator of Climate Change

Abstract: Variations in the length of the snow-cover season affect the albedo which in turn impacts the energy balance; thus, it is important to have a data set concerned with the spatial and the temporal character of snow. Data on the date when the arctic snow cover disappears in the spring is presented and analyzed for 12 stations between 68 and 74?N latitude. For a few of the stations, data are available for over 50 yr; however, Soviet data are available only from the late 1930s until the mid 1950s, and Canadian data have only been recorded since the late 1950s. Results show that for much of the North American arctic tundra the date of snow disappearance has been occurring earlier in the spring since the late 1960s. For Barrow, Alaska, there has been a trend towards earlier snowmelt since about 1950. It is not yet apparent as to whether this trend can be attributed to increases in carbon dioxide and soot in the arctic environment or whether a particular circulation regime, such as a shift in the location of the polar vortex, may be responsible. But because the Arctic is where anthropogenic atmospheric pollution is expected to have the largest impact on climate, and in view of anticipated increased future emissions of carbon dioxide and soot, a more complete and lengthy snow-cover data set may provide an early indication of the onset of the predicted warming of the polar climate.

Water content effects on photosynthetic response of Sphagnum mosses from the foothills of the Philip Smith Mountains, Alaska.

Abstract: In tussock tundra areas of the foothills north of the Brooks Range, Alaska, up to two-thirds of annual precipitation may occur during intermittent summer thunderstorms. The seasonal pattern in capitulum water content of Sphagnum spp. depends on the frequency and duration of these precipitation events, on the microtopography of the habitat including depth of thaw, and on morphological characteristics of the individual species. The response of net photosynthesis to varying water content in Sphagnum squarrosum and S. angustifolium growing under willow canopies in a tussock tundra area near the Dalton Highway on the North Slope of Alaska was examined in the field. After a period in June required to develop photosynthetic capability, capitula water content was essentially optimal for photosynthesis in the range from 6 to 10 g H2O/g DW. Above this range, the rate of CO2 uptake was reduced, presumably due to limitations on CO2 diffusion to the photosynthetically active sites. At water contents below the optimum, net photosynthesis fell rapidly until reaching compensation at approximately 1 g H2O/g DW. Dependent on changes in weather conditions, average water content of Sphagnum samples collected in the field occasionally fell below 5 g H2O/g DW. During a particularly dry period, water content of individual Sphagnum hummocks fell below 1 g H2O/g DW, indicating that water stress does limit Sphagnum photosynthetic production in this habitat.

Contribution palynostratigraphique (dinokystes, pollen et spores) à la connaissance de la mer de Champlain: coupe de Saint-Césaire, Québec

Abstract: High-resolution continental (pollen and spores) and marine (dinoflagellate cysts) microfloral records were obtained from a section consisting of about 0.5 m of glaciolacustrine and 2.5 m of Champlain Sea deposits at the Saint-Cesaire site. The pollen and spore assemblages indicate the existence of a regional open vegetation of shrub tundra to forest tundra. Fluctuations in the percentages of Picea and shrub and herb taxa are related to regional afforestation and paleogeographical evolution of the basin. The Champlain Sea sediments contain an abundant dinocyst flora dominated by Operculodinium centrocarpum, Brigantedinium spp., and Algidasphaeridium? minutum, which indicate cold Arctic conditions in surface waters. Fluctuations in concentration (102–104∙cm−3) and relative abundance of dinocyst species are attributed to changes in dinoflagellate productivity and paleoceanographic conditions, notably paleosalinity. Morphological variations of Operculodinium centrocarpum and Algidasphaeridium? minutum led to ...

Standing biomass and production in water drainages of the foothills of the Philip Smith Mountains, Alaska

Abstract: In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra is the most widely distributed vegetation, and it occurs on rolling hills and in valleys that were shaped by a sequence of Pleistocene glaciations. In this study, aboveground standing biomass and production were compared in “intertrack tundra” areas that were relatively homogenous with respect to downslope drainage and adjacent “water tracks” that acted to channel water flow to the valley bottom stream. Comparisons of biomass, leaf area index, and specific leaf weight were also made between upper and lower slope positions. Similarities and differences of vegetation structure are examined with respect to graminoid, deciduous shrub, evergreen shrub, herbaceous, and bryophyte components. Water tracks were found to have 1.5–1.7 times the biomass of intertrack tundra, and production (excluding secondary growth) in water tracks was 40% greater than in intertrack tundra. The aboveground biomass for all areas studied and the annual production values were similar to those found in other studies of tussock tundra. While only slight differences in depth of thaw occurred in water tracks and intertrack tundra during June and early July, water tracks thawed more deeply with the onset of summer rains. Warmer temperatures at 40 cm depth in July and August may have increased nutrient availability, whereas greater rooting depth and movement of water may have increased nutrient capture in water tracks as compared with the intertrack areas. Greater biomass and a deeper thaw depth occurred at upper slope locations.

The developmental history of Adirondack (N.Y.) lakes

Abstract: We utilized paleoecological techniques to reconstruct long-term changes in lake-water chemistry, lake trophic state, and watershed vegetation and soils for three lakes located on an elevational gradient (661–1150 m) in the High Peaks region of the Adirondack Mountains of New York State (U.S.A.). Diatoms were used to reconstruct pH and trophic state. Sedimentary chrysophytes, chlorophylls and carotenoids supplied corroborating evidence. Pollen, plant macrofossils, and metals provided information on watershed vegetation, soils, and biogeochemical processes. All three lakes were slightly alkaline pH 7–8) and more productive in the late-glacial. They acidified and became less productive at the end of the late-glacial and in the early Holocene. pH stabilized 8000–9000 yr B.P. at the two higher sites and by 6000 yr B.P. at the lowest. An elevational gradient in pH existed throughout the Holocene. The highest site had a mean Holocene pH close to or below 5; the lowest site fluctuated around a mean of 6. The higher pH and trophic state of the late-glacial was controlled by leaching of base cations from fresh unweathered till, a process accelerated by the development of histosols in the watersheds as spruce-dominated woodlands replaced tundra. An apparent pulse of lake productivity at the late-glacial-Holocene boundary is correlated with a transient, but significant, expansion of alder (Alnus crispa) populations. The alder phase had a significant impact on watershed (and hence lake) biogeochemistry. The limnological changes of the Holocene and the differences between lakes were a function of an elevational gradient in temperature, hydrology (higher precipitation and lower evapotranspiration at higher elevation), soil thickness (thinner tills at higher elevation), soil type (histosols at higher elevation), vegetation (northern hardwoods at lower elevation, spruce-fir at higher), and different Holocene vegetational sequences in the three watersheds.

A tundra-steppe transition on kathul mountain, alaska, u.s.a.

Abstract: Paleoecological data do not permit a definitive characterization of the treeless vegetation that covered unglaciated interior Alaska during the last glacial period. Knowledge of the potential ranges of modern taxa can help determine which species could have comprised full-glacial plant communities. Azonal grassland (steppe) communities that currently occupy steep southfacing bluffs within the boreal forest of interior Alaska contain species that may have been more widespread during the full glacial. In order to investigate the potential ecological range of steppe taxa we studied the vegetation at Kathul Mountain, where continuous treeless vegetation occurs from low elevation to alpine tundra. The results from 27 vegetation plots placed along an elevational gradient from 290 to 910 m suggest a gradual transition from steppe to tundra. Species responded individualistically to changing elevation, and steppe and tundra taxa were intermixed over a broad zone of intermediate elevation. Two important steppe taxa, Agropyron spicatum and Artemisiafrigida, were consistently present to elevations over 800 m. Regression of DCA scores on environmental variables indicated that both the interaction of slope and aspect and elevation were important factors controlling vegetation composition. Assuming that changes in elevation, slope, and aspect cause a change in temperature and growing-season length, it appears that some steppe taxa could have survived full-glacial conditions, at least on lower-elevation slopes with a south-facing aspect. The vegetation on such sites during the last glacial period may have been similar to that of the tundra-steppe transition seen today at Kathul Mountain.

Nutrient and water flux in a small arctic watershed: an overview

Abstract: The “Response, Resistance, Resilience to, and Recovery from Disturbance in Arctic Ecosystems” (R4D) program initially concentrated on impacts of altered water and nutrient inputs on tussock tundra vegetation. The intensive site is at Imnavait Creek (68°C 37′ N, 149° 17′ E), near Toolik Lake. Alaska in the foothills of the Brooks Range, approximately 200 km south of Prudhoe Bay. Tussock tundra was selected for initial study because it has an extensive distribution in the Alaskan Arctic (80% of the arctic region), the majority of the pipeline corridor north of the Brooks Range passes through tussock tundra, and disturbances of arctic tundra are expected to occur in the future. Also important is that 18% of the circumpolar arctic primary productivity and 47% of the circumpolar arctic stored carbon are in tussock tundra. Water and nutrient additions were performed because they frequently accompany disturbance and development in the Arctic. Emphasis was placed on determining responses of physical, physiological, and ecosystem processes to environmental change in such a way that extrapolations to other areas would be facilitated. The hills near Imnavait Creek are covered by glacial till of the Sagavanirktok River glaciation. with a deep organic layer on the less exposed hill slopes and valleys. The vegetation is dominated by Eriophorum vaginatum L., Betula nana L., Vaccirtium uliginosum L, Vaccinium viiis-idaea L., Ledum palustre L., Salix pulcbra L., and Sphagnum spp. Winds were rarely calm but seldom exceed 17 m s−1, generally from the east-southeast to the south-southwest (66%). Precipitation in 1986 was 344 mm, about half of which was snowfall. Mean temperature in 1986 was −8.1°C, with an absolute minimum of −43°C. Mean July temperature was between 9.8 and 13.7°C. Nutrients are more mobile than previously thought, moving an estimated 10 m downslope in the first growing season. It underscores the importance of the winter environment to biological and hydrological processes. Greater water flow results in increased plant growth rates, leaf area, and biomass. Effects of changes in nutrient and water supply on photosynthesis were minimal. Where increases in productivity took place, they occurred more likely as a result of changes in allocation patterns, including an initial redirection of carbohydrate stores to new leaf development, than from increases in photosynthetic rates. The work reported here indicates that the downslope transmission of nutrient and water flow effects caused by altered drainage and nutrient supply may result in a larger area of impact than previously thought.

Competition causes regular spacing of alder in Alaskan shrub tundra.

Abstract: Alders (Alnus crispa) in shrub tundra in northern Alaska showed significant regularity of spacing. Removal of neighboring alder shrubs stimulated nutrient accumulation and growth of remaining alders but did not stimulate nutrient accumulation or growth of any other shrub species. This demonstrates that neighboring alders competed with one another and that, when alders were removed, the resources made available were used preferentially by remaining alders rather than by the community in general. Neither patterns of seedling establishment nor patterns of frostrelated features could explain the regular distribution of alder. We suggest that regular patterns of plant distribution are restricted to sites of low-resource availability, because in these habitats (1) there is strong competition for a scarce resource, and (2) there are only one or a few dominant species to compete for these resources in a given canopy height or rooting depth.

Stable isotope analysis of carbon flow in a tundra river system

Abstract: Stable isotope analysis was used to identify the major sources of carbon utilized by fish and aquatic invertebrates in the Koroc River, a tundra river system in northern Quebec. Juvenile arctic char (Salvelinus alpinus), together with adults and juveniles of other species of fish in freshwater, obtained their carbon from either allochthonous or autochthonous sources within the river system, via the invertebrate fauna. However, adult anadromous char caught in the river clearly derived their biomass carbon from feeding at sea. Despite the limited development of riparian vegetation throughout much of the lower river catchment, terrestrial organic matter was the most likely source of energy fueling the animal communities of small tributary streams and rapids of the mainstem Koroc. In contrast, epilithic algae made a significant contribution to food chains within Alik Lake, a deep basin along the main river channel. Aquatic mosses appeared to be of, at most, tertiary importance as a source of energy to the ani...

Maximum CO2-assimilation rates of vascular plants on an Alaskan arctic tundra slope

Abstract: Light-saturated CO2-assimilation rates of 19 vascular plant species were measured on a tundra slope in the foothills of the Brooks Range, Alaska. Maximum assimilation capacities on a leaf area basis ranged from 20.3 μmol m−2 s−1 for the forb, Bistorta plumosa, to 6.0 μmol m−2 s−1 for the evergreen, Empetrum hermaphroditicum. Graminoids, deciduous shrubs, and forbs fell within a similar range of maximum photosynthetic rates on a leaf area basis. Evergreens had the lowest rates. On a leaf weight basis, maximum assimilation rates were greatest for forbs, followed by deciduous shrubs, graminoids, and evergreens. Rates of evergreens were less than half those of all other growth forms. Cassiope tetragona had the lowest rates per unit leaf weight of any species tested; mean maximum rates of C. tetragona were only 14% of those of B. plumosa, the species with the highest rates. When the data were subjected to canonical analysis, only a partial correspondence was found between species growth form and photosynthetic characteristics.

Wetland Soils and Vegetation, Arctic Foothills, Alaska.

Abstract: : Analyses of relationships between hydric soils and wetland plant species were made at a site in the northern foothills of the Brooks Range, Alaska, as part of a cooperative effort between the US Fish and Wildlife Service and Soil Conservation Service to develop methods for field identification of wetlands and hydric soils The site is considered to be representative of broad regions of acidic tussock tundra in the foothills Seven soil types (subgroups) were identified at the site All except two are considered hydric

Role of the seed bank in providing colonizers on a tundra disturbance in Alaska

Abstract: Numbers of germinable seeds in soils from four undisturbed communities at an Alaskan Arctic Coastal Plain site ranged from 70 to 600 m−2 and numbers of distinct taxa were two to nine. Stratified soils contained more germinable taxa than unstratified soils, suggesting that seed banks in Alaskan tundra are more diverse than shown by earlier studies using unstratified soils. In contrast to temperate seed banks, which often contain early successional species no longer present in the vegetation, all seed bank taxa at this site occur within a short distance of the sample sites because of long persistence of the communities. Of the common colonizers on a nearby 30-year-old disturbance, Betula nana, Poa arctica, Salix spp., and Arctagrostis latifolia are absent or present in only small amounts in the seed bank and apparently colonize mainly from seeds dispersed following disturbance. Eriophorum angustifolium, another common colonizer, is present in the seed bank of wet areas and Carex bigelowii and C. aquatilis a...

In situ estimates of annual net nitrogen mineralization and nitrification in a subarctic watershed.

Abstract: Annual estimates of surface soil nitrogen transformations were determined using an in situ method in four different subarctic vegetation types within a watershed in southwestern Alaska. The net nitrogen mineralization estimates were 22.5, 0.5, 4.7, and 2.7 kg-N ha-1 yr-1 for the alder, dry tundra, moist tundra, and white spruce sites, respectively. Only the soil from the alder site showed net nitrification (about 10 kg-N ha-1 yr-1). Annual inogranic nitrogen flux from the overlying organic layer to the mineral soil was almost seven times greater than net N production in the surface mineral soil in the alder site, indicating that the alder forest floor is potentially a substantial source for plant-available N. Rates of mobilization of N from the surface organic layers of the other sites were similar to net N production rates in surface mineral soils. In situ rates of N transformations showed a similar trend among sites as did laboratory estimates conducted in a previous study, suggesting a strong substrate control of N transformations in these soils.

Limitations on Sphagnum growth and net primary production in the foothills of the Philip Smith Mountains, Alaska.

Abstract: In the foothills of the Philip Smith Mountains, Brooks Range, Alaska, tussock tundra occurs on rolling hills and in valleys that were shaped by Pleistocene glaciations. During the 1986 and 1987 summer seasons, Sphagnum growth and production were determined in "water tracks" on tundra slopes that acted to channel water flow to the valley bottom stream and in "intertrack tundra" areas that were relatively homogeneous with respect to downslope drainage. Measurements were made under ambient environmental conditions and on mosses receiving supplemental irrigation in each area. Growth rate for Sphagnum spp. (cm shoot length increase/day) was low and relatively constant in intertrack tundra and highest but quite variable in water tracks. A strong negative correlation was found between Sphagnum spp. growth rate and solar irradiance in the shady environment below Salix canopies in the water tracks. Estimates of net annual dry weight (DW) production for Sphagnum spp. ranged from 0.10 g DW dm-2 yr-1 in intertrack tundra vegetation to 1.64 g DW dm-2 yr-1 in well-shaded water tracks. Experimental water additions had little effect on growth and production in intertrack tundra and well-developed water tracks, but significantly increased growth in a weakly-developed water track community. Low production over large areas of tundra slopes may occur due to presence of slow growing species resistant to dessication in intertrack tundra as opposed to rapidly growing less compact species within the limited extent of water tracks. We hypothesize that species capable of rapid growth occur also in weakly-developed water tracks, and that these are water-limited more often than plants occurring in well-developed water track situations. Where experienced, high light intensity may additionally limit growth due to photoinhibition.

Recent retrogression of the forest-alpine tundra ecotone (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) in the Scandes Mountains, Sweden

Abstract: Demography of mountain birch (Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) was studied in permanent plots (1972/73-85/86), in the forest- alpine tundra ecotone of the Swedish Scandes Mountains. The censused tree population, which to a large extent became established in response to the climatic warming c. 1915-50, declined in certain respects during the study period. A sympathetic cooling trend for the summers, and a few years with relatively severe and protracted snowpack influences were recorded for the study area. The number of tree-sized birches decreased by c. 16%, while sexual regeneration failed and many individuals declined in vigour. The major cause of mortality and vigour decline was mechanical stress, imposed by delayed snowmelt, possibly in combination with age-related mechanical weakening. A measure of tree-line inertia in relation to climatic variability was obtained by extrapolating the demographic trend of the study period indefinitely. Given the same degree of thermal change, extinction of the birch tree-line population needs much more time than establishing it.

Some physical and chemical characteristics of an arctic beaded stream

Abstract: Imnavait Creek is a tundra stream in the Arctic Foothills of Alaska. The stream is beaded, i.e. consists of pools (up to ∼ 2 m deep) connected by narrow channels. Peat dominates pool and channel substrate materials with occasional rock and moss substrates. The watershed is underlain by ice-bonded till and is hydrologically watertight. Because of low rates of weathering, bedrock and till do not contribute significantly to ionic composition of the stream water. Breakup occurs in late May to early June with surface flow until September. During periods of low rainfall, channel flow is reduced and pools become hydrologically isolated and thermally stratified (with very high surface water temperatures). Streamwater is acidic (pH values 5.3–6.1) with very low alkalinity (≤3 mg l−1). The major transport of ions occurs in early flow derived from snow melt. Organic carbon concentrations are high with very high ratios of dissolved to particulate organic carbon. Dissolved inorganic nitrogen concentrations appear to be very low. High concentrations of dissolved organic material may indicate a central role for DOM in trophic dynamics.

Temperate and polar zonobiomes of Northern Eurasia

Abstract: 1: Zonobiome VI: The Temperate Nemoral Zones of Europe.- 1.0 Introduction.- 1.1 Climate.- 1.2 The Soils.- 1.3 The Producers.- 1.3.1 Subzonobiome (oc) with the Atlantic Heath Areas.- 1.3.2 Subzonobiome (eumi) with Central European Vegetation.- 1.3.3 Subzonobiome (miru) of the Deciduous Forests of Eastern Europe..- 1.4 Consumers.- 1.4.1 Introduction.- 1.4.2 Habitat Diversity and the Importance of Seasonal Change to the Fauna of Deciduous Forests.- 1.4.3 An Ecological Survey of the Forest Fauna.- 1.4.4 Some Aspects of Nutritional Requirements and Related Special Features of the Fauna of Deciduous Forests.- 1.4.5 Summary of the Zooecological Aspects of a Central European Deciduous Forest.- 1.5 The Decomposers.- 1.6 Ecological Investigations and Ecosystem Research.- 1.6.1 Adaption to a Cold Season (Hardening).- 1.6.2 Cold Resistance of the Herbaceous Undergrowth.- 1.6.3 Ecophysiology of Nemoral Tree Species.- 1.6.4 Ecophysiology of the Herbaceous Layer.- 1.6.5 Ecosystems.- 1.7 Subdivision of Zonobiome VI in Europe.- 1.8 Orobiome VI: the Northern Edge of the Alps.- 1.8.1 The Climate of the Alps.- 1.8.2 The Soils of the Alps.- 1.8.3 The Producers.- 1.8.4 The Northern Carpathians.- 1.9 Pedobiomes of ZB VI.- 1.9.1 Amphibiomes and Helobiomes of Riverine Floodplains.- 1.9.2 Halo- and Psammobiomes of the Sea Coasts.- 1.10 Zonoecotones.- 1.10.1 Zonoecotone VI/VIII of the Boreal-Nemoral Mixed Deciduous-Coniferous Forests of Europe.- 1.10.2 Zonoecotones VI/VII of the Forest Steppe of Eastern Europe..- 2: Subzonobiome VII of the Semi-Arid Steppes of Eurasia.- 2.0.1 General Introductory Remarks on Zonobiome VII.- 2.0.2 The Forest Steppe as Transitional Zone (Zonoecotone VI/VII)..- 2.1 The Climate.- 2.2 The Soils.- 2.3 The Producers.- 2.3.1 Typical Meadow Steppe (Festuceta herbeta) on Thick Chernozem..- 2.3.2 Feathergrass Steppe.- 2.3.3 Sage-Feathergrass Steppe (Artemisieto-Stipetum) on Lightly Solonized Chestnut Earth (Castanozem).- 2.3.4 Ecophysiology of the Steppe Plants.- 2.3.5 Peri-glacial Steppe Relicts in Central Europe.- 2.3.6 West-Siberian Steppes.- 2.3.7 East-Asian Steppe.- 2.4 The Consumers.- 2.5 The Decomposers.- 2.6 Steppe Ecosystems.- 2.7 Subdivision of Steppes into Subzonobiomes and Biomes.- 2.8 The Orobiomes of the Steppe Zone.- 2.9 Pedobiomes of the Steppe Zone.- 2.10 Zonoecotone VII/VIII in Siberia.- 2.10.1 Climatic Conditions.- 2.10.2 Soil Conditions.- 2.10.3 Floristic Relationships.- 2.10.4 Ecological Investigations.- 2.10.5 Phytomass of the Pine Stands.- 2.10.6 The Natural Rejuvenation of Pine Forests.- 3: Subzonobiome VIIa of the Arid Semi-Desert in the Caspian Lowland.- 3.0 General.- 3.1 The Climate.- 3.2 The Soils.- 3.3 The Producers.- 4: Subzonobiome VIIa of the Arid Semi-Deserts and Deserts of Kazakhstan.- 4.0 General.- 4.1 The Climate.- 4.2 The Soils.- 4.3 The Producers.- 4.3.1 Ecological Investigations.- 4.4 The Consumers.- 4.5 The Decomposers.- 4.6 Ecosystem Research.- 4.7 Subdivision of the Kazakhian Semi-Desert into Biomes.- 4.8 Orobiomes.- 4.9 Pedobiomes.- 5: Subzonobiome VII (rIII) of the Extremely Arid Deserts of Middle Asia: the Biome Group Middle Asia.- 5.0 General.- 5.1 The Climate.- 5.2 The Soils.- 5.3 The Producers.- 5.3.1 Halobiomes or Salt Deserts.- 5.3.2 The Takyry.- 5.3.3 Deserts with Ephemeral Vegetation.- 5.3.4 The Sand Desert of Central Karakum.- 5.4 The Consumers.- 5.5 The Decomposers.- 5.6 Quantitative Ecosystem Research.- 5.7 Subdivision of Middle Asia into Biomes.- 5.8 Orobiome VII (rIII) of Middle Asia.- 5.8.1 The Kopet Dagh Mountains.- 5.8.2 The Tien Shan Mountains and the Pamiro-Alai System.- 5.9 Pedobiomes: Amphibiomes of the Floodplains of the Amu-Darya..- 5.10 Zonoecotone to the Deserts of Central Asia.- 6: Extremely Arid Subzonobiome VII (rIII) of the Central Asian Deserts.- 6.0 General.- 6.1 Transitional Region to Outer Mongolia (excluding the Gobi Desert).- 6.2 The Gobi Desert.- 6.2.1 General.- 6.2.2 Ecological Investigations in the Northern Gobi.- 6.3 The Pei Shan Desert.- 6.4 The Tarim Basin with the Takla Makan Desert.- 6.5 Kansu or Hessi Corridor.- 6.6 The Ala Shan Desert.- 6.7 The Ordos Desert.- 6.8 The Tsaidam Basin (Transitional to the Cold Plateaux).- 7: Extremely Cold-Arid Subzonobiome VII (tIX) of the Cold and High Plateau Deserts of Central Asia.- 7.0 General Situation of the Cold Deserts of the High Mountain Plateaux of Asia.- 7.1 The High Plateau of Tibet.- 7.2 The Pamirs - an Ecologically Well-Studied High-Mountain-Desert.- 7.2.0 General Subdivision.- 7.2.1 The Eastern Pamir.- 7.2.2 The Western Pamir and Badakhshan.- 8: Zonobiome VIII of the Boreal Conifer Zone (Taiga) of Euro-Siberia.- 8.0 Introduction.- 8.1 The Climate (Subzonobiomes).- 8.2 Zonal Soils.- 8.3 The Producers.- 8.3.1 The European Taiga.- 8.3.2 The Siberian Taiga.- 8.4 The Consumers.- 8.5 The Decomposers.- 8.6 Ecosystems of Zonobiome VIII.- 8.6.1 Competition on Spruce-Forest Ecosystems.- 8.6.2 Ecosystem Studies Including Data on Production.- 8.6.3 Optimal Production Values in Natural Conifer Forests.- 8.6.4 Fruit Production and Rejuvenation.- 8.7 Subdivision of Zonobiome VIII.- 8.8 The Orobiome of Zonobiome VIII.- 8.9 Pedobiomes of Zonobiome VIII.- 8.9.1 The Peino-Helobiome of the Oligotrophic Bogs.- 8.9.2 Ecology of Raised Bogs.- 8.9.3 The Consumers of Bogs.- 8.9.4 The Largest Bog Area of the World in Western Siberia.- 8.9.5 Amphibiomes: Boreal Flood-Plain Forests.- 8.10. Zonoecotone VIII/IX: the Forest Tundra.- 9: Zonobiome IX: The Arctic Tundra of Eurasia.- 9.1 Climate.- 9.2 The Soils.- 9.3 The Producers.- 9.4 The Consumers.- 9.5 The Decomposers.- 9.6 Ecosystem Research.- 9.6.1 Subzonobiome of the Southern Tundra.- 9.6.2 Subzonobiome of the Typical Tundra.- 9.6.3 Subzonobiome of the Northern Tundra.- 9.6.4 Subzonobiome of the Arctic Desert.- 9.6.5 Productivity and the Cycling of Matter in Zonobiome IX of Eurosiberia.- 9.7 The Subdivision of the Arctic ZB IX.- 9.8 Orobiomes IX of the Tundra Region.- 9.9 Arctic Pedobiomes.- 9.10. The Zonoecotone of Perpetual Snow Patches.- 10: Interzonal and Multizonal Orobiomes of Euro-Siberia.- 10.0 General.- 10.1 The Crimean Mountains.- 10.2 The Ural Mountains.- 10.3 The Altai Mountains.- 10.4 The Caucasian Mountains.- References.

Mapping Arctic tundra vegetation types using digital SPOT/HRV-XS data A preliminary assessment

Abstract: Multispectral (XS) image data recorded by the High Resolution Visible (HRV) sensor aboard the SPOT-1 satellite are being evaluated for the mapping of Arctic tundra vegetation in the Arctic Foothill Province of Alaska. This research is part of a current ecosystems study that requires an efficient means for mapping vegetation types over large areas. Conventional spectral-based image classification techniques were applied to SPOT/HRV-XS data from a single date. The unique characteristics of the vegetation cover (mainly tussock tundra) and illumination conditions of the location necessitated a detailed examination of classification approaches that have generally been applied in mid-latitude studies. Preliminary results suggest that areal estimates of Arctic tundra vegetation types can be made accurately (±2·5 per cent per category), but maps generated by classifying spectral features of SPOT/HRV-XS data alone arc unsuitably accurate (56 per cent). This is partly due to the high occurrence of relative...

Variability of macroinvertebrate community composition in an arctic and subarctic stream

Abstract: The macroinvertebrate community composition was compared in two Alaskan streams (USA) for numeric and species constancy during the ice-free period from 1981 to 1983. Imnavait Creek is a first order arctic stream (60° 39′ N, 149° 21′ W) draining upland tundra in the foothills of the Brooks Range. Caribou-Poker Creek is a 4th order subarctic stream (65° 08′ N, 147° 28′ W) draining the taiga forest north of Fairbanks, Alaska. The aquatic insect larvae and other macroinvertebrates were sampled with drift nets and Hess bottom samplers for four periods, each 1 week long in the ice free season of three years. We found 112 species in the arctic stream and 138 species in the subarctic stream in a chironomid-dominated community. In any sample period the communities contained 51–60 species in the arctic and 49–92 species in the subarctic. Between the four sample periods on average 39% and 50% of the species were present in two sequential samples in the arctic and subarctic stream, respectively. New immigrants, never before found in the system, averaged 37% and 31 % of the community, respectively. These systems are exposed to several intermediate disturbances: prolonged and variable freeze-up, extreme variation in discharge, wide diel and seasonal changes in temperature, and erosion by frazil and anchor ice. The dipterans that compose the most numerous and variable taxa must have variable diapause, ability to grow in cold waters, and good dispersal powers, even migrating across drainages in the arctic. Much of the seasonal dominance pattern appears therefore to be stochastic.

T1he effects of winier seismic trails on tundra vegetation in northeastern alaska, u.s.a.

Abstract: The effects of winter seismic trails on tundra vegetation were studied on the Coastal Plain of the Arctic National Wildlife Refuge. Seismic exploration occurred during the winters of 1984 and 1985. Thirty-four permanent study plots were established the following summers, representing the range of disturbance which occurred in each of seven major vegetation types. Plots were visited two of the first three summers after disturbance. At each plot plant cover was measured using a point frame, disturbance characteristics were recorded, and ground surface elevations were surveyed. Plant cover was lower on most disturbed plots than on their adjacent controls, with decreases as high as 87%o the first summer following disturbance. The species most sensitive to disturbance were evergreen shrubs, followed by willows, tussock sedges, and lichens. Willow height in riparian shrubland plots was significantly reduced by 5 to 11 cm (from an average of 16 cm, p<0.05). Little recovery of plants occurred in the second or third summers after disturbance; only four plots in river floodplain habitats (Dryas terrace and riparian shrubland) showed improvements in cover of a few species. Track depressions ranging from 5 to 15 cm occurred at three plots in moist sedge-shrub tundra and increased significantly (p<0.05) at one plot between the first and third summers following disturbance. Continuation of this study will provide information on the long-term impacts and recovery rates of winter seismic trails.

Late Quaternary chronology and environments of Square Lake, Torngat Mountains, Labrador

Abstract: Sediment, pollen, and diatom records from Square Lake, a small lake dammed by a segment of Saglek Moraine, cover the period of deposition of and deglaciation from the Saglek Moraine. The basal radiocarbon date (18 210 ± 1900 years BP) is on sediment contaminated by reworked pollen and is thus a maximum age. However, the date was measured on organic carbon recovered from glaciolacustrine couplets associated with deposition of the Saglek Moraine and thus establishes a Late Wisconsinan age for the Saglek Moraine. Vegetation on the ice-free upland surrounding Square Lake at this time was a sparse tundra vegetation dominated by grasses and herbs. The absence of diatoms indicates perennial lake-ice cover. A major transition is recorded by pollen and diatoms at > 8.5 ka. Vegetation probably remained sparse tundra, but birch and willow may have arrived in the area by 8 ka. Diatoms are first dominated by alkaliphil species, reflecting continued influence of glaciolacustrine sedimentation. An abrupt change in depos...

Evapotranspiration from the Alpine Tundra of Colorado, U.S.A.

Abstract: An electronic load-cell weighing lysimeter was used for measuring daily evapotranspiration from the alpine tundra on Niwot Ridge in the Front Range, Colorado, during the 1987 growing season. Concom...