Modern pollen data from the Canadian Arctic, 1972-1973

This data descriptor reports results of a 1972–73 baseline study of modern pollen deposition in the Canadian Arctic to originally aid interpretation of Holocene pollen diagrams from that region, especially focussed on the arctic tree-line. The data set is geographically unique due to its extent, and allows the assessment of the effects of modern climate change on northern ecosystems, including fluctuations of the a arctic tree-line. Repeated sampling was conducted along an interior transect at 29 sites from the Boreal Forest to the High Arctic, with five additional coastal sites covering a total distance of 3,200 km. Static pollen samplers captured both local pollen and long-distance pollen wind-blown from the Boreal Forest. Moss and lichen polsters provided multi-year pollen fallout to assess the effectiveness of the static pollen samplers. The local vegetation was recorded at each site. This descriptor provides information on data archived at the World Data Center PANGAEA, which includes spreadsheets detailing site and sample information as well as raw and processed pollen data obtained on over 500 samples.

Vegetation of the Continental Northwest Territories at 6 ka BP

Pollen records are used to reconstruct vegetation in the continental Northwest Territories at 6 ka (6000 14C yr BP). Picea glauca, P mariana, Larix laricina, Populus tremuloides, P. balsamifera, Alnus crispa and A. incana were present throughout their modern ranges in the Boreal and Subarctic Forest Zones by 6000 BP. Pinus banksiana, however, had not yet reached its present northern limits. Population densities of the dominant trees, Picea glauca and Picea mariana, were close to, or as high as, present. In the Mackenzie Delta region the range limit of Picea glauca was approximately 25 km north of its modern location just prior to 6000 BP. In contrast, the northern limits of the forest in central Canada were similar to present. The tundra vegetation close to the edge of the forest was similar to modern Low Arctic Tundra. Development of extensive Sphagnum peatlands had begun in the forested areas and the adjacent Low Arctic Tundra. Palaeoecological information regarding vegetation at 6000 BP remains lacking for the northeastern half of the study area. Therefore, the nature of the vegetation in much of the area now occupied by Low Arctic and Middle Arctic Tundra remains unknown. Important vegetation changes that occurred following 6 ka include : (1) the advance of Pinus banksiana to its present northern range limits, (2) the retreat of the northern range limits of Picea glauca in the Mackenzie Delta region between 6000 and 3500 BP and (3) the rapid and marked increase in the population density of Picea mariana in the treeline zone of the central Northwest Territories at 5000 BP followed by a decline at 4000 BP.

Paléophytogéographie et paléoclimats postglaciaires dans l’ouest du Bas-Saint-Laurent, Québec

L'analyse pollinique des sédiments de quatre lacs du Bas-Saint-Laurent et de la Côte-du-Sud permet de retracer l'existence d'une phase initiale de toundra s'étendant sur une durée estimée à 500-1000 ans, après à la déglaciation. Cette toundra montre un développement progressif à partir d'un quasi-désert jusqu'à un stade arbustif à bouleau glanduleux, en passant par un stade herbacé riche en plantes arctiques-alpines dont la présence est confirmée par l'analyse macrofossile. L'accumulation organique dans les lacs ne survient que vers 9500-9200 BP, soit plus de 2000 ans après la déglaciation, et correspond à l'arrivée des premiers arbres, d'après les macrorestes. Le tardiglaciaire régional paraît donc avoir été climatiquement très rigoureux par rapport aux régions sises au sud-ouest et au sud, dans les Appalaches. Les forêts sont restées ouvertes jusque vers 8000 BP, constituées surtout de l'épinette noire, des peupliers, du mélèze et du bouleau blanc. La zone pollinique correspondante est dominée par l'aulne crispé, qui a dû jouer un rôle important dans le couvert végétal durant une période caractérisée par une forte incidence des feux. Par la suite, la végétation moderne s'est établie, soit une mosaïque de sapinières et d'érablières avec sensiblement les mêmes séquences physiographiques et les mêmes gradients phytogéographiques régionaux que ceux actuellement constatés dans ce secteur des Appalaches. Les cédrières tourbeuses et les sapinières humides à thuya répandues actuellement dans les basses terres estuariennes et à la marge nord du plateau appalachien ne se sont toutefois développées que vers 3600 ans avant l'actuel. L'Optimum climatique holocene n'est clairement marqué que par une plus grande abondance du pin blanc de 7000 à 3600 ans BP, notamment à la marge nord du plateau appalachien.

A middle Pleistocene paleosol sequence from Dawson Range, Central Yukon Territory

Four paleosols were intersected in a core drilled into the colluvial fill of a largely buried meltwater channel that was last active during the youngest of the pre-Reid glaciation (0.99-0.78 Ma) in the Dawson Range, Yukon Territory. The paleosols are classified as Podzols. The sedimentary sequence and paleosols indicate that at least two middle Pleistocene glacial and interglacial periods are represented in the core. The mean annual temperature exceeded 0° C for thousands of years in the upland environment of the Dawson Range at 61° N during these interglacial periods.

Holocene vegetation history of Banks Island, Northwest Territories, Canada

Four pollen diagrams from Banks Island, Northwest Territories, provide the first records of the postglacial vegetation of the region. Chronologies are estimated from radiocarbon dates and by correlation of the exotic-pollen curves to data from the mainland. The pollen stratigraphies from all sites can be divided into three zones, where the middle zone, dating from 7000 to 2000 BP, corresponds to the warmest time. Although both the first and third zones correspond to cooler periods, the vegetation of the earliest zone was not identical to that of the latest, indicated by lower frequencies of key pollen types such as those of Dryas and Saxifraga.Key words: Banks Island, Holocene, pollen diagram, Arctic, paleoecology, Quaternary.

Current trends in studies of long-term plant community dynamics

Long-term plant community dynamics has been investigated by analyses of macro- and microfossil remains found in unconsolidated limnic and terrestrial sediments, chiefly of Late-Quaternary and Recent age. Plant macrofossils preserved in packrat (Neotoma) midden sites in semi-arid regions have yielded the most informative data for the period between the lastest glacial to the present day. The remains can, with few exceptions, be identified to species level, they represent a large (>75%) proportion of the species composition of vegetation within a radius of 30-50 m of a site, and they can be dated by the accelerator mass-spectrometric radiocarbon method. Most sites have been found in the arid southwest of the United States and significant contributions have been made recently to understanding of long-term changes in species composition and shifts in range and elevational limits of species. Similarly, analysis of macrofossils in lake, mire and river sites can draw on the taxonomic precision, small source area and potential for precise radiocarbon dating of samples, to provide detailed reconstructions of the local vegetation of lacustrine, mire and fluvial habitats. The vast literature reporting these investigations deals with sites chiefly in northern temperate regions, but recent studies from tropical and warm-temperate regions show the promise of the approach. The use of analyses of microscopic charcoal preserved in sediments has increased significantly in the past few decades as part of attempts to reconstruct forest tire history and, when combined with other analyses (pollen, physical chemistry), to investigate past community dynamics. The major limitations of the method are poor chronological control in many sediments, uncertainties about source area and limited taxonomic precision. On the other hand, macroscopic remains of charcoal can usually be identified to species level, can be dated accurately and have readily defined source areas. However, sites with high frequencies of sample occurrence spanning long, continuous time intervals are very rare, as a remarkable example from the humid tropics of Africa illustrates. Pollen analysis of lake and mire sediments has a long history and has yielded a vast literature. Its weaknesses as a tool in the three main fields of interest where it is used - palaeoclimatology, cultural history and plant community dynamics are well known and increase in regions farther north and south of the boreal and Contents Summary 469 I. Introduction 470 II. Types of evidence 471 III. Problems and prospects 487 Acknowledgements 490 References 490.