Holocene Treeline History and Climate Change Across Northern Eurasia

Abstract

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5°to 7.0°C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation.

Late Glacial and Holocene changes in vegetation cover and climate in southern Siberia derived from a 15 kyr long pollen record from Lake Kotokel

“…This feature is in good agreement with other pollen records from the Lake Baikal region and from the broader areas of Siberia (e.g. MacDonald et al, 2000;Bezrukova et al, 2005;Demske et al, 2005;Andreev and Tarasov, 2007). The reconstructed 10% decrease in woody cover percentages dated to ca.…”

Late Quaternary vegetation-climate feedbacks

“…Past, 5, 203-216, 2009 www. During the mid-Holocene some 6000 years ago, boreal forests extended north of the modern tree line (Frenzel et al, 1992;TEMPO et al 1996;Cheddadi et al, 1997;Tarasov et al, 1998;Prentice and Webb III, 1998;MacDonald et al, 2000). These differences between mid-Holocene and present boreal biome patterns were presumably caused by steady changes in the Earth's orbit which led to stronger insolation (incoming solar energy flux density) than today and stronger near-surface warming during Northern Hemisphere summer.…”

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“…Present-day extension of larch in the Arctic is limited mainly by the mean July isotherm of 10-12°C (MacDonald et al, 2000). It is plausible that the western foreland of the Verkhoyansk Mountains, the area where the Dyanushka Peat and Lake Billyakh are located, with its numerous lake and river valleys provided enough moisture and warm microhabitats to buffer larch trees against climatic extremes.…”

“…Botanical records from high-latitude regions of Europe and North America indicate that boreal forests "became established during the Holocene interglacial (the past 11.6 ka) as a result of population invasion from southern glacial refugia and local expansion of small tree populations that survived the Last Glacial Maximum interval (LGM: ~25-17 ka) in cryptic refugia" (Petit et al, 2008). An extensive dataset of radiocarbon-dated macrofossils from northern Asia provides evidence that boreal trees advanced close to the current arctic coastline between 9 and 7 ka (MacDonald et al, 2000). Due to a lack of wood macrofossils older than 10 ka from the 2000×2500 km 2 region of eastern Siberia between 108° and 145°E (Fig.…”