Dwarf Shrub Tundra Research Articles

Late-glacial vegetation dynamics of the Queen Charlotte Islands and adjacent continental shelf, British Columbia, Canada

AMS radiocarbon dates and paleoecological analyses of sediments from the continental shelf between the Queen Charlotte Islands and the British Columbia mainland confirm that portions of the shelf were subaerially exposed and ice-free between at least 14,330 and 12,860 14C years BP (17,370–14,570 cal years BP). Pollen analysis suggests that Cyperaceae likely formed the dominant plant cover on the exposed shelf at Dogfish Bank, and fossil Pediastrum algae confirm the presence of freshwater. Pollen accumulation rates suggest low plant density on the exposed shelf, although this is uncertain due to over- and under-representation of some pollen types in relation to vegetation abundance on the landscape. Paleoecological analyses of late-glacial sediments at West Side Pond on the southern Queen Charlotte Islands demonstrate succession from herb tundra dominated by Cyperaceae at 13,750 14C years BP (16,830 cal years BP) to dwarf shrub tundra with Salix and Empetrum nigrum after 13,500 14C years BP (16,400 cal years BP). Pteridophytes increased in abundance during the transition to Pinus contorta woodland ca. 13,000 14C years BP (15,600 cal years BP). Fossil conifer stomata suggest that P. contorta grew locally as early as 13,040 ± 305 14C years BP. Alnus crispa was co-dominant by 11,500 14C years BP (13,500 cal years BP), and Picea sitchensis or its hybrids were present as early as 11,400 14C years BP (13,400 cal years BP) in the south Moresby area.

The Circumpolar Arctic vegetation map

Abstract. Question: What are the major vegetation units in the Arctic, what is their composition, and how are they distributed among major bioclimate subzones and countries? Location: The Arctic tundra region, north of the tree line. Methods: A photo-interpretive approach was used to delineate the vegetation onto an Advanced Very High Resolution Radiometer (AVHRR) base image. Mapping experts within nine Arctic regions prepared draft maps using geographic information technology (ArcInfo) of their portion of the Arctic, and these were later synthesized to make the final map. Area analysis of the map was done according to bioclimate subzones, and country. The integrated mapping procedures resulted in other maps of vegetation, topography, soils, landscapes, lake cover, substrate pH, and above-ground biomass. Results: The final map was published at 1:7 500 000 scale map. Within the Arctic (total area = 7.11 × 106 km2), about 5.05 × 106 km2 is vegetated. The remainder is ice covered. The map legend generally portrays the zonal vegetation within each map polygon. About 26% of the vegetated area is erect shrublands, 18% peaty graminoid tundras, 13% mountain complexes, 12% barrens, 11% mineral graminoid tundras, 11% prostrate-shrub tundras, and 7% wetlands. Canada has by far the most terrain in the High Arctic mostly associated with abundant barren types and prostrate dwarf-shrub tundra, whereas Russia has the largest area in the Low Arctic, predominantly low-shrub tundra. Conclusions: The CAVM is the first vegetation map of an entire global biome at a comparable resolution. The consistent treatment of the vegetation across the circumpolar Arctic, abundant ancillary material, and digital database should promote the application to numerous land-use, and climate-change applications and will make updating the map relatively easy.

Tundra Fire and Vegetation Change along a Hillslope on the Seward Peninsula, Alaska, U.S.A

A 1977 tundra fire burned a hillslope where prefire soils and vegetation ranged from poorly drained moist tussock-shrub tundra on the lower slopes to well-drained dwarf shrub tundra on the back slope and very poorly drained wet sedge meadow on the flat crest. We sampled the vegetation on this slope before the fire and at 8 sites following the fire at irregular intervals from 1 yr to 25 yr. During the first decade after the fire, short-term recovery was dominated by bryophytes, sedges, and grasses from both regrowing sedge tussocks and seedlings. However, during the second and third decade, and by 24 yr after the fire, evergreen (Ledum palustre) and deciduous shrubs (mainly Salix pulchra willow) expanded dramatically so that shrub cover was generally higher than before the fire. Labrador tea has increased by vegetative means on the poorly drained lowest 3 tussock-shrub tundra sites. Upslope on the better-drained and more severely burned tussock-shrub and dwarf shrub tundra sites, willows became established from seed mainly during the first 10 yr after the fire and, based on their relatively large size (0.5–1 m tall) and cover, have grown rapidly during the past 15 to 20 yr. There has been very little or no recovery of Sphagnum moss and fruticose lichens after 24 yr at any site, except for Sphagnum moss in the wet meadow site. The permafrost active layer thickness has diminished to prefire levels at the lower slope tussock-shrub tundra sites but is much greater or degraded completely on the steeper slope, corresponding with the distribution of willow shrub colonization. These changes in tundra vegetation and permafrost following fire suggest that such fires could accelerate the predicted effects of climate warming on ecosystems in the Arctic.

Pollen‐vegetation calibration for tundra communities in the Arctic Foothills, northern Alaska

Summary 1 Palynology has been portrayed as a ‘blunt’ tool for reconstructing variations in arctic tundra vegetation. We tested this characterization in the Arctic Foothills of northern Alaska by analysing 56 modern pollen assemblages from lakes on contrasting glaciated surfaces. The two surfaces, which date to the Sagavanirktok (> 125 000 years BP) and Itkillik II ( c. 11 500 years BP) ice advances from the Brooks Range, have considerably different geomorphology, soil characteristics and plant communities. Sagavanirktok surfaces are dominated by dwarf-shrub tundra (DST), and Itkillik II surfaces by prostrateshrub tundra (PST). 2 We used two multivariate approaches, dissimilarity metrics (squared chord distance and Canberra metric distance) and discriminant analysis, to assess the ability of the pollen data to distinguish between the Sagavanirktok and Itkillik II landscapes, and to identify the taxa most strongly associated with one surface or the other. Receiver operating characteristic (ROC) analysis was used to evaluate the performance of the dissimilarity metrics and to determine their ‘critical values’ for distinguishing between assemblages from like and unlike plant communities. 3 According to the discriminant analysis, taxa indicative of the Sagavanirktok surface include Rubus chamaemorus , Sphagnum and Ericales, whereas Equisetum , Thalictrum and Polypodiaceae were faithful to the Itkillik II surface. These differences between the pollen assemblages make it possible to differentiate between the two landscapes using Canberra metric distance comparisons. The ROC analysis demonstrated that the Canberra metric distance is more effective than squared chord distance for distinguishing between the two surfaces. This study illustrates that palynology can be used to explore questions regarding the landscape-scale heterogeneity of past tundra vegetation.

Holocene pollen records from the central Arctic Foothills, northern Alaska: testing the role of substrate in the response of tundra to climate change

1 To explore the role of edaphic controls in the response of arctic tundra to climate change, we analysed Holocene pollen records from lakes in northern Alaska located on glaciated surfaces with contrasting soil texture, topography and tundra communities. Using indicator taxa, pollen accumulation rates (PARs) and multivariate comparison of fossil and modern pollen assemblages, we reconstructed the vegetational changes at Upper Capsule Lake (Sagavanirktok surface) and Red Green Lake (Itkillik II surface) in response to increased effective moisture between the early and middle Holocene. 2 In the Red Green record, low PARs and the continuous presence of taxa indicative of prostrate-shrub tundra (PST; Equisetum, Polypodiaceae, Thalictrum and Rosaceae) indicate that the vegetation resembled PST throughout the Holocene. During the warm, dry early Holocene (11 300–10 000 cal years BP), PST also occurred on Sagavanirktok surfaces, as evidenced by PST indicators (Bryidae, Polypodiaceae, Equisetum and Rosaceae) in this interval of the Upper Capsule record. However, PARs increased, suggesting increased vegetation cover, PST taxa declined and taxa indicative of dwarf-shrub tundra (DST; Rubus chamaemorus and Lycopodium annotinum) increased between 10 000 and 7500 cal years BP. 3 We hypothesize that between the early and middle Holocene the fine-textured soils and smooth topography of Sagavanirktok surfaces led to increased soil moisture, greater vegetation cover, permafrost aggradation, anoxic and acidic soil conditions, slower decomposition and the development of a thick organic layer. In contrast, soil moisture remained low on the better-drained Itkillik II surface, and vegetational changes were minor. 4 Landscape-scale substrate variations have an effect on how tundra responds to climate change, suggesting that the response of arctic ecosystems to future variability may be spatially heterogeneous.

Post‐glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut, Canada

AbstractClimate models suggest that the global warming during the early to mid‐Holocene may have partly resulted from the northward advance of the northern treeline and subsequent reduction of the planetary albedo. We investigated the Holocene vegetation history of low arctic continental Nunavut, Canada, from a radiocarbon‐dated sediment core from TK‐2 Lake, a small‐lake ca. 200 km north of the limit of the forest‐tundra. The pollen and loss‐on‐ignition data indicate the presence of dwarf shrub tundra in the region since the beginning of organic sedimentation at ca. 9000 cal. yr BP with dominance of Betula, especially since 8700 cal. yr BP. At 8100–7900 cal. yr BP the dominance of the shrub tundra was punctuated by a transient decline of Betula and coincident increases of Ericaceae undiff., Vaccinium‐type, and Gramineae. This suggests an abrupt disturbance of the Betula glandulosa population, approximately simultaneously with the sudden 8200 cal. yr BP event in the North Atlantic. However, in the absence of other sites studied in the area, linkage to the 8200 cal. yr BP event remains tentative. The lack of any evidence of forest‐tundra in the region constrains the northern limit of the mid‐Holocene advance of the forest‐tundra boundary in central northern Canada. Consequently, our results show that the climate models imposing a mid‐Holocene advance of the limit of the forest‐tundra to the arctic coast of Canada may have overestimated the positive climatic feedback effects that can result from the replacement of tundra by the boreal forest. Copyright © 2003 John Wiley & Sons, Ltd.

Late Weichselian (Valdaian) and Holocene vegetation and environmental history of the northern Timan Ridge, European Arctic Russia

Lake and peat deposits from the Timan Ridge, Arctic Russia, were pollen analysed, reconstructing the vegetation history and paleoenvironment since the Last Glacial Maximum (LGM) 20–18,000 years ago. The sites studied are located inside the margins of a large paleolake of about 20 km 2 , by us named Lake Timan. This lake developed in the Late Weichselian, more than 30,000 years after the deglaciation of this region, and was formed due to increased precipitation and warmer summers that accelerated the melting of stagnant ice within its catchment. The lake was drained during the early Holocene when the outlet rivers eroded the spillways. A new generation of much smaller lakes formed during the Holocene when the last remnants of buried glacier ice melted away causing the exposed floor of Lake Timan to subside. Since deglaciation, the following regional vegetation development has been recorded: (1) During the initial stage of Lake Timan, the dominant vegetation was discontinuous steppe/tundra, with patches of snow bed vegetation. (2) A dwarf-shrub tundra established during the Late Weichselian interstadial (Aller ød), probably reflecting warmer and moister conditions. (3) The Younger Dryas cooling is recognised by a reversal to steppe/tundra and snowbeds on unstable mineral-soils, and higher palynological richness. (4) Soon after the transition into the Holocene, a birch-forest established on the Timan Ridge. (5) A cooling starting around 8200 cal. years BP initiated the deforestation of the exposed hills. In the most protected sites, birch trees persisted until later than 4000 years ago, reflecting a gradual development into the present treeless dwarf-shrub tundra.

Environmental control and intersite variations of phenolics in Betula nana in tundra ecosystems

• Secondary metabolites make leaves unpalatable for herbivores and influence decomposition. Site-specific differences are presented in phenolics and nitrogen in Betula nana leaves from dwarf shrub tundra at Abisko, northern Sweden, and from tussock tundra at Toolik Lake, Alaska, subjected to a decade of warming, fertilization and shading. • Nitrogen and a number of phenolics, including condensed and hydrolysable tannins, flavonoids, phenolic glucosides and chlorogenic acids, were analysed in B. nana leaves. • Phenolic concentrations showed marked between-site differences (e.g. condensed tannins were 50% higher at Abisko than at Toolik); responses to the environmental manipulations were more pronounced at Toolik compared with Abisko. Warming increased condensed tannins and decreased hydrolysable tannins at Toolik, but had no effect at Abisko, whereas fertilization and shading generally decreased concentrations. • Betula invests less carbon in phenolics at Toolik than at Abisko and shows a greater response to environmental changes by investing more carbon in growth and less to phenolic production. Hence, the Toolik population has a lower herbivore-defense level, which declines further if nutrient availability increases. By contrast, under warmer conditions, the increase in bulk phenolics and decrease in leaf palatability are greater at Toolik than at Abisko.

Holocene pollen stratigraphy indicating climatic and tree-line changes derived from a peat section at Ortino, in the Pechora lowland, northern Russia

This study presents the results of pollen analysis and radiocarbon dates of a peat section from Ortino, in the Pechora lowland in northern Russia. A pollen stratigraphy is provided for at least the last 9200 years and it provides a basis for the reconstruction of the vegetational and mire history in the northernmost part of European Russia. Conifer stomata content was recorded as a complement to pollen studies to achieve a better resolution of tree-line fluctuations. The onset of Holocene warming initiated a vegetation succession that started first with herb-dominated tundra vegetation, and later with herb-shrub tundra. Combined pollen and stomata evidence suggests that Picea accompanied by Betula spp. spread to Ortino soon after 9000 14C yr BP. Trees and a climate warmer than at present persisted until c. 3000 14C yr BP, when forests disappeared and modern dwarf-shrub tundra vegetation developed.

Lateglacial and Early Holocene environments inferred from a tufa deposit at Fyledalen, S. Sweden

A reinvestigation of a tufa deposit in Skåne, including a number of biostratigraphical methods and chronology was carried out. The tufa was formed in a paludal environment during the time period c. 9,500 to 8,000 BP. This period is characterised by exceptional low lake levels and high summer temperatures in southern Sweden. This may suggest that optimal conditions for tufa formation at the site coincided with warm and dry climate conditions, a low groundwater table, and high evaporation. During periods with colder conditions and/or higher groundwater table peat was deposited. The changes in the local environment at and around the site were inferred from the biostratigraphical records of pollen, plant macrofossils, molluscs, and insects. The results demonstrate a development from a dwarf shrub tundra during the Late-glacial, which turned to an open birch/pine woodland around 10,000 BP. At c. 9,000 BP hazel and birch were probably the dominant tree species in the woodland. The mollusc record suggests that the woodland remained relatively open until c. 8,500 BP when tree taxa such as alder, oak and elm became established in the Fyledalen valley. The site remained a marsh throughout the studied period, however, the results indicate a succession of different marsh plant communities.

Landsat MSS-derived land-cover map of northern Alaska: Extrapolation methods and a comparison with photo-interpreted and AVHRR-derived maps

Vegetation maps of Arctic areas are needed for a variety of tundra ecosystem and climate change studies and for extrapolating from relatively small, well-known sites to broader regions. We made a preliminary land-cover map of northern Alaska by extrapolating a Landsat Multi-Spectral Scanner (MSS) derived classification of the Kuparuk River Region (KRR) to all of northern Alaska. We used a 26-scene mosaic that was previously made by the EROS Data Center, and a K-means unsupervised classification algorithm to produce eight broad land-cover categories. The northern Alaska-MSS map (NA-MSS) has the following land-cover categories and respective percentage coverage within the 200000km2 Arctic Slope: Dry Prostrate-shrub Tundra and Barrens, 8%; Moist Graminoid, Prostrate-shrub Tundra, 22%; Moist Tussock-graminoid, Dwarf-shrub Tundra, 4%; Moist Dwarf-shrub, Tussock-graminoid, Tundra, 28%; Moist Lowshrub Tundra and other Shrublands, 19%; Wet Graminoid Tundra, 9%; Water, 6%; Clouds and ice, <1%; Shadows, 4%. Ancillary data were used to improve the classification for a region of sandy tundra not encountered in the KRR and to separate shadows in the mountains from water and wetlands elsewhere. The NA-MSS map helps to define the distribution of a recently described moist nonacidic (calcareous) tundra and areas of shrublands that are of broad interest to the tundra- and climate-change modelling communities. A boundary separating moist acidic tundra from moist nonacidic tundra stretches across all of northern Alaska (about 850km). Shrub-dominated tundra is prevalent in the southern and western (warmer, wetter) portions of the map. We created difference maps for comparing the northern Alaska-MSS (NA-MSS) map to the Major Ecosystems of Alaska (MEA) map and a map derived from a time series of Advanced Very High Resolution Radiometer images (NA-AVHRR). Compared to the other maps, the NA-MSS map provides more detailed information for moist tundra areas and shows more shrub-dominated vegetation with different spatial distributions than the other two maps. An accuracy assessment of the map will be performed in 1999.

Devensian organic interstadial deposits and ice sheet extent in Buchan, Scotland

Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary. © 1998 John Wiley & Sons, Ltd.

Devensian organic interstadial deposits and ice sheet extent in Buchan, Scotland

Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary. © 1998 John Wiley & Sons, Ltd.

The Quaternary vegetation and landscape evolution of Novaya Zemlya in the light of palynological records

The paper presents the results of paleoenvironmental (pollen) investigations of Novaya Zemlya throughout all the Quaternary, including Eopleistocene, Pleistocene and Holocene. Clear evidence of continuity between the modern flora and paleofloras confirms the lack of sharp and continuous interruptions in the vegetation development in high latitudes as well as the absence of gigantic ice sheets in the Eastern Arctic. During the Eopleistocene plant communities varied from Boreal meadow coenoses in the south of Novaya Zemlya to Arctic tundra in the north. During the Lower Pleistocene the climate had deteriorated considerably, but still remained warmer than today's. There were two cold (=glacial) and two warm (=interglacial) stages in the Upper Pleistocene. The older interglacial, Kumzha, was marked by rather mild climate and extensive marine transgression. During the climatic optimum southern dwarf shrub tundra grew in the Southern Island, but forest did not penetrate there. The younger interglacial, Krestyakhino, had cooler climate and more restricted transgression extent. Typical tundra existed in the Southern Island. The Upper Pleistocene glaciations were no more extensive than nowadays and large biota refuges existed in the coastal and even some inner areas of Novaya Zemlya at least between 15,000 and 10,000 BP. During the Holocene, great change took place at the end of climatic optimum when dwarf shrub tundra was replaced by more open tundra communities.

Diurnal and Seasonal Patterns of Ecosystem CO 2 Efflux from Upland Tundra in the Foothills of the Brooks Range, Alaska, U.S.A.

Carbon dioxide efflux and soil microenvironment were measured in three upland tundra communities in the foothills of the Brooks Range in arctic Alaska to determine the magnitude of CO{sub 2} efflux rates and the relative importance of the belowground factors that influence them. Gas exchange and soil microenvironment measurements were made weekly between 14 June and 31 July 1990. The study communities included lichen-heath, a sparse community vegetated by lichens and dwarf ericaceous shrubs on rocky soils, moist Cassiope dwarf-shrub heath tundra, dominated by Carex and evergreen and deciduous shrubs on relatively deep organic soils, and dry Cassiope dwarf-shrub heath of stone-stripe areas, which was of intermediate character. Rates of CO{sub 2} efflux were similar for the three communities until mid-season when they peaked at rates between 4.9 and 5.9 g m{sup {minus}2} d{sup {minus}1}. Following the mid-season peak, the rates in all three communities declined, particularly in the lichen-heath. Seasonal patterns of CO{sub 2} efflux, soil temperature, and soil moisture suggest changing limitations to CO{sub 2} efflux, soil temperature, and soil moisture suggest changing limitations to CO{sub 2} efflux over the course of the season. Rates of carbon dioxide efflux followed changes in soil temperature early in the seasonmore » when soil moisture was highest. Mid-season efflux appeared to be limited by soil, moss, and lichen hydration until the end of July, when temperature again limited efflux. Differences between the communities were related to microenvironmental differences and probable differences in carbon quality. The presence of peat-forming mosses is suggested to play an important role in differences in efflux and micro-environment among the communities. 32 refs., 3 figs., 4 tab.« less

Submerged late quaternary terrestrial deposits and paleoenvironment of northern Hecate Strait, British Columbia continental shelf, Canada

Stratigraphic and paleoenvironmental analyses of sediments recovered from cores on the western Canadian continental shelf indicate that areas of the north-central shelf were subaerial and supported terrestrial vegetation during the regional Late Wisconsinan deglaciation. Paleoecological analyses of now submerged shelf sediments reveal a Late Quaternary treeless environment locally covered by wet sedge tundra. Samples from a coeval onshore section on eastern Graham Island indicate that a dwarf shrub tundra with mosses and willows also occupied lowland areas on the Queen Charlotte Islands between 13 and 14 ka. Ice-free subaerial conditions persisted for a period of at least 3200 years on some parts of the emergent shelf, between 13.2 and 10 ka. During the same time period clay-rich glaciomarine sediment with ice-rafted debris was accumulating in the troughs of the shelf. Low relative sea levels during deglaciation on the continental shelf adjacent to the eastern Queen Charlotte Islands suggest that Late Wisconsinan ice was thin and limited in extent in this area. The presence of a habitable lowland environment during this time interval strengthens the view that a coastal migration of humans from Beringia was possible along portions of the exposed continental shelf.

Detection and Classification of Muskox Habitat on Banks Island, Northwest Territories, Canada, Using Landsat Thematic Mapper Data

The feasibility of using Landsat Thematic Mapper data for mapping muskox summer habitat was tested on northern Banks Island, Northwest Territories. Digital image enhancement and classification techniques were examined to determine if summer foraging habitats could be detected and mapped using Thematic Mapper imagery. Interpretations of the satellite data were verified in the field during the summers of 1988 and 1989. The most important summer foraging habitats for muskoxen included the wet sedge meadow, graminoid tundra and graminoid/dwarf shrub tundra cover types. These lowland habitats were generally distinguishable on enhanced colour images and were easily differentiated from upland areas. The most suitable colour composite for differentiating muskox summer habitats was the near-infrared (band 4), shortwave infrared (band 5) and red (band 3) spectral bands displayed in red, green and blue respectively. Upland cover types, including dwarf shrub tundra, hummocky tundra and dwarf shrub/lichen barrens, were more difficult to differentiate because of spectral variability resulting from differences in plant cover and site characteristics. The classified image had an overall accuracy of 88%. The summer habitats of particular importance to muskoxen had classification accuracies of 84-89%. Detection of important foraging habitats on Thematic Mapper imagery is attributable to the spectral distinctiveness of wet graminoid communities and the high spectral sensitivity and spatial resolution of the infrared sensors, which allow detection of differences in surface moisture and vegetation physiognomy.Key words: bison habitat, boreal forest, digital image analysis, supervised classification, Landsat Thematic Mapper data, habitat mapping, Bison bison athubuscue, remote sensing

Late Wisconsin white spruce (Picea glauca (Moench) Voss) at Brampton, Ontario

Study of late Wisconsin deposits in a small bog on the crest of Brampton esker (mantled by the Halton Till), about 30 km west of Toronto, Ontario, yielded a radiocarbon date of 12 320 ± 360 years BP (BGS-551) for a sample of white spruce cones that contained fully-developed seeds. This date on cones (in gyttja) provides an estimate of minimum age for the lower boundary of the spruce pollen zone in southern Ontario. Silty clay beneath the gyttja yielded leaves of Dryas integrifolia and pollen assemblages (a herb pollen zone) that indicate presence of a dwarf-shrub tundra (essentially treeless) type of vegetation.This study supports the Port Huron Stadial age (about 13 000 years BP) of the Halton Till that underlies the silty clay, and suggests an age of between 12 500 – 13 000 years BP for glacial Lake Peel in the Brampton area that preceded the glacial Lake Iroquois phase in the Lake Ontario basin.

Nutrient turnover studies in Alpine ecosystems : II. Phytomass and nutrient relations in the Caricetum firmae.

1. A plot of the Caricetum firmae in the Northern Calcareous Alps (at 2,160 m above sea level) was investigated during the growing season 1973 with regard to dry matter, nitrogen, phosphorus, and potassium content of overground and underground phytomass, including accumulated litter. 2. Compared to another habitat of the same community at 2,010 m a.s.l., the overground phytomass in the state of maximum development (ca.250 g per m2) and the store of nutrients (4 g N, 0.25 g P and 2.4 g K per m2) are nealy, the same, but the primary production is less (ca. 100 g as against ca. 160 g per m2). 3. The accumulation of litter in relation to the annual overground production is nearly 30:1. 4. The content of N, P, and K in the predominant species Carex firma and Dryas octopetala ranks near the inferior limit known for terrestrial plants. The minimum values are attained in the state of maximum development (mid-August). 5. The mineralization of N amounts to about 2 g per m2 during the growing season and thus exceeds the quantity that enters into the overground production. The maximum mineralization is found 5 to 10 cm under the soil surface. In this layer most of the fine roots are concentrated. 6. The lactate-soluble content of P and K in the soil averages ca. 0.3 or 1.5 per m2 and decreases from the beginning to the height of the growing season by ca. 0.35 or 0.5 g per m2 with a slight increase toward the end. In the field incubation experiments losses of P and K, interpreted as microbial incorporation, prevailed during the growing season. It was hardly possible to determine evident relations between the fluctuations of P and K in the soil and those in the phytomass. 7. The Caricetum firmae ranks between the "typical arctic tundra" and the "dwarf-shrub tundra" with regard to the obtained data on phytomass, primary production, and nutrients, except for the underground production which seems to be remarkably higher.