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A Holocene History of Changes in Northern Russian Treelines
Reference
MacDonald, G.M., Kremenetski, K.V. and Beilman, D.W. 2008. Climate change and the northern Russian treeline zone. Philosophical Transactions of the Royal Society B 363: 2285-2299.

What was done
Noting that the location of the northern Russian treeline "is largely controlled by summer temperatures and growing season length," the authors conducted an analysis of past changes in the treeline of this region -- as reconstructed from tree-ring data and radiocarbon-dated subfossil wood -- in an attempt to answer the question: "Has the pattern of recent warming over the late nineteenth and the twentieth centuries caused significant changes in the density of trees at the treeline and/or an extension of the geographical location of the treeline?"

What was learned
MacDonald et al. report that "temperature increases over the past century are already producing demonstrable changes in the population density of trees, but these changes have not yet generated an extension of conifer species' limits to or beyond the former positions occupied during the Medieval Warm Period (MWP: ca AD 800-1300) or the Holocene Thermal Maximum treeline extension (HTM: broadly taken here to be ca 10,000-3,000 years ago)."

Of the Khibiny uplands of the central Kola Peninsula, for example, they write that "the treeline was located 100-140 m higher in elevation than today during the MWP," and that "forest has yet to recolonize these elevations (Kremenetski et al., 2004)." Likewise, of the northern Polar Urals they say "the treeline was at its highest elevation during the MWP between ca AD 900 and 1300 when it reached 340 m," after which it "descended to approximately 270 m during the Little Ice Age and then ascended to its present elevation of approximately 310 m during the recent warming of the late nineteenth and twentieth centuries."

What it means
The three researchers conclude that "at the Russian sites studied, the impact of twentieth century warming has not yet compensated fully for the mortality and range constriction caused by the cold temperatures of the Little Ice Age," and they note that "these results are similar to observations in some other northern treeline regions such as uplands in eastern Quebec and interior Labrador where Picea mariana (P. Mill.) B.S.P. and Picea glauca (Moench) Voss trees remain below their pre-Little Ice Age limits despite recent warming (Gamache and Payette,2005; Payette, 2007)," which warming has likely not yet equaled that of the MWP in either magnitude or duration or possibly even both.

References
Gamache, I. and Payette, S. 2005. Latitudinal response of subarctic tree lines to recent climate change in Eastern Canada. Journal of Biogeography 32: 849-862.

Kremenetski, K.V., Boettger, T., MacDonald, G.M., Vaschalova, T., Sulerzhitsky, L. and Hiller, A. 2004. Medieval climate warming and aridity as indicated by multiproxy evidence from the Kola Peninsula, Russia. Palaeogeography and Palaeoclimate 209: 113-125.

Payette, S. 2007. Contrasted dynamics of northern Labrador tree lines caused by climate change and migrational lag. Ecology 88: 770-780.

Reviewed 6 August 2008