Aage Paus

Climate change and Arctic ecosystems: 1. Vegetation changes north of 55°N between the last glacial maximum, mid-Holocene, and present

A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55°N at the last glacial maximum (LGM) and mid-Holocene (6000 years B.P.). The pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf-shrub tundra, erect dwarf-shrub tundra, and low- and high-shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra-forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid-Holocene the tundra-forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (∼200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (∼200 km). Low- and high-shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf-shrub, erect dwarf-shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low- and high-shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.

Climate change and Arctic ecosystems: 1. Vegetation changes north of 55 degrees N between the last glacial maximum, mid-Holocene, and present

A unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55°N at the last glacial maximum (LGM) and mid-Holocene (6000 years B.P.). The pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups. Five tundra types (cushion forb tundra, graminoid and forb tundra, prostrate dwarf-shrub tundra, erect dwarf-shrub tundra, and low- and high-shrub tundra) were distinguished and mapped on the basis of modern pollen surface samples. The tundra-forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed. During the mid-Holocene the tundra-forest boundary was north of its present position in some regions, but the pattern of this shift was strongly asymmetrical around the pole, with the largest northward shift in central Siberia (∼200 km), little change in Beringia, and a southward shift in Keewatin and Labrador (∼200 km). Low- and high-shrub tundra extended farther north than today. At the LGM, forests were absent from high latitudes. Graminoid and forb tundra abutted on temperate steppe in northwestern Eurasia while prostrate dwarf-shrub, erect dwarf-shrub, and graminoid and forb tundra formed a mosaic in Beringia. Graminoid and forb tundra is restricted today and does not form a large continuous biome, but the pollen data show that it was far more extensive at the LGM, while low- and high-shrub tundra were greatly reduced, illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types.

Late Weichselian vegetation, climate and floral migration at Eigebakken, South Rogaland, southwestern Norway

Paus, Aa., 1989. Late Weichselian vegetation, climate and floral migration at Eigebakken, South Rogaland, southwestern Norway. Rev. Palaeobot. Palynol., 61:177 203.

The Late Weichselian and early Holocene history of tree birch in south Norway and the Bølling Betula time-lag in northwest Europe

This study compares late-glacial pollen data from northwest Europe to elucidate the northward migration of tree birch during the Bolling warming about 13,000 BP and the subsequent birch-forest development. The late-glacial tree-birch history in south Norway is emphasized. The Bolling warming initiated a rapid northward migration of tree birch, that extended across most of northwest Europe within c. 300 yr. Comparison of pollen influx studies shows that values of about 200 tree-birch pollen grains cm−2a−1 indicate local tree birch. The time that elapsed between the Bolling warming and the local birch-forest development, the so-called Bolling Betula time-lag, lasted up to 1000 yr, though in southern and/or protected sites this lag was about 500 yr or even less. In all areas of northwest Europe, strong winds are assumed to have been an important factor that delayed the birch-forest development in the first half of the late-glacial. Other important factors were drought effects in southern areas (e.g. south Britain) and sparse snow cover and frost in northern areas. The Arctic treeline lay in north Rogaland, southwest Norway, about 12,500 BP. During the Allerod Chronozone, tree birch migrated northward along the ice-free coastal strip of south Norway to More and Romsdal. However, the development of Allerod birch forest in Norway was restricted to Rogaland. The Younger Dryas cooling (11,000–10,000 BP) caused the near-extinction of tree birch in Norway, and only in sheltered sites in south Rogaland scattered individuals were able to survive. Hence, vegetational boundaries crossed Rogaland, thus representing an ecotonal area, through major parts of the late-glacial. A rapid development of closed birch forests all along the coast of south Norway occurred after the Holocene warming (10,000 BP).

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 meltingof stag nant ice within its catchment. The lake was drained duringthe 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^d), 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 dwarfshrub tundra. r 2003 Elsevier Science Ltd. All rights reserved.

Early Weichselian palaeoenvironments reconstructed from a mega‐scale thrust‐fault complex, Kanin Peninsula, northwestern Russia

A section, almost 20 km long and up to 80 m high, through alternating layers of diamict and sorted sediments is superbly exposed on the north coast of the Kanin Peninsula, northwestern Russia. The diamicts represent multiple glacial advances by the Barents Sea and the Kara Sea ice sheets during the Weichselian. The diamicts and stratigraphically older lacustrine, fluvial and shallow marine sediments have been thrust as nappes by the Barents Sea and Kara Sea ice sheets. Based on stratigraphic position, OSL dating, sea level information and pollen, it is evident that the sorted sediments were deposited in the Late Eemian-Early Weichselian. Sedimentation started in lake basins and continued in shallow marine embayments when the lakes opened to the sea. The observed transition from lacustrine to shallow marine sedimentation could represent coastal retreat during stable or rising sea level.

Early- to mid-Holocene forest-line and climate dynamics in southern Scandes mountains inferred from contrasting megafossil and pollen data:

The result of 344 radiocarbon-dated megafossils is here presented and discussed. This study aims at elucidating early- to mid-Holocene forest-line and climate dynamics in the southern Scandes along a present gradient of decreasing forest-line elevations. Around 9.5 calibrated ka before present (BP), pine suddenly established vertical belts of at least 200 m. These represent the highest pine-forests during the Holocene, ca. 210–170 m higher than today when corrected for land uplift. By this, summer temperatures at least 1–1.3°C warmer than today are indicated for the early Holocene thermal maximum around 8.5–9.5 cal. ka BP. The most pronounced warming occurred in Jotunheimen, the highest mountain range in Scandinavia, because of an amplified ‘Massenerhebung’ effect. Megafossils show the establishment of birch-forests above pine-forests already from the early Holocene. Pine-forests started their decline in the early Holocene and became replaced by the less warmth-demanding birch-forests. Pine megafossil results and pollen studies from the same areas show that cooling around 8.5 cal. ka BP caused a significant decrease in pine pollen production whereas pine-forest-lines were more or less unaffected. In the following period of about 2000 years, the high-altitudinal pine-forests could hardly be detected in pollen diagrams. This shows how strongly past temperatures influenced on the pollen production of individuals and how this might obscure pollen-based reconstructions of past vegetation. To be able to correct for this error, there is a need for establishing exact present-day relationships between temperature and pollen production of prolific pollen producers.

Long-term changes in regional vegetation cover along the west coast of southern Norway: The importance of human impact

Special Feature “Millennial to centennial vegetation change” (Eds. Thomas Giesecke, Petr Kuneš & Triin Reitalu). 1Department of Natural History, University Museum, University of Bergen, Bergen, Norway 2Department of Biological Sciences, University of Bergen, Bergen, Norway 3Museum of Archaeology, University of Stavanger, Stavanger, Norway 4Institute of Ecology, Tallinn University, Tallinn, Estonia 5Museum of Cultural History, University of Oslo, Oslo, Norway