CPD Climate of the Past Discussions CPD 1814-9359 Copernicus GmbH Göttingen, Germany 10.5194/cpd-4-741-2008 Eliminating the "divergence problem" at Alaska's northern treeline Wilmking M. 1 Singh J. 1 Institute of Botany and Landscape Ecology, Grimmer Strasse 88, Greifswald University, 17487 Greifswald, Germany 11 06 2008 4 3 741 759 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.clim-past-discuss.net/4/741/2008/cpd-4-741-2008.html The full text article is available as a PDF file from http://www.clim-past-discuss.net/4/741/2008/cpd-4-741-2008.pdf

Recently, an increasing off-set between tree-ring based temperature reconstructions and measured temperatures at high latitudes has been reported, the so called "divergence problem" (here "divergence effect"). This "divergence effect" seriously questions the validity of tree-ring based climate reconstructions, since it seems to violate the assumption of a stable response of trees to changing climate over time. In this study we eliminated the "divergence effect" in northern Alaska by careful selection of individual trees with consistently significant positive relationships with climate (17% of sample) and successfully attempted a divergence-free climate reconstruction using this sub-set. However, the majority of trees (83%) did not adhere to the uniformitarian principle as usually applied in dendroclimatology. Our results thus support the notion, that factors acting on an individual tree basis are the primary causes for the "divergence effect" (at least in northern Alaska). Neither different detrending methods nor factors acting on larger scales such as global dimming or an increase in UV-B radiation could explain our results. Our results also highlight the necessity to adapt the methods of paleoreconstruction using tree rings to account for non-stable climate growth relationships as these are found in the vast majority of sampled trees and seem to be the norm rather than the exception.

 References Barber, V., Juday, G. P., and Finney, B.: Reduced growth of Alaska white spruce in the twentieth century from temperature-induced drought stress, Nature, 405, 668–672, 2000. Biondi, F. and Waikul, K.: DENDROCLIM2002: a C++ program for statistical calibration of climate signals in tree-ring chronologies, Computers and Geosciences, 30, 303–311, 2004. Briffa, K. R., Jones, P. D., Bartholin, T. S., et al.: Fennoscandian summers from A.D. 500: temperature changes on short and long timescales, Clim. Dynam., 7, 111–119, 1992. Briffa, K. R., Schweingruber, F. H., Jones, P. D., and Osborn, T.: Reduced sensitivity of recent tree growth to temperature at high northern latitudes, Nature, 391, 678–682, 1998a. Briffa, K. R., Schweingruber, F. H., Jones, P. D., et al.: Trees tell of past climates: but are they speaking less clearly today?, Philosophical Transactions of the Royal Society of London B, 353, 65–73, 1998b. Briffa, K. R., Osborn, T. J., and Schweingruber, F. H.: Large-scale temperature inferences from tree rings: a review, Global Planet. Change, 40, 11–26, 2004. Bunn, A. G., Goetz, S. J., Kimball, J. S., and Zhang, K.: Northern high latitude ecosystems respond to recent climate change, Eos, 88, 333–335, 2007. Cook, E. R., Esper, J., and D'Arrigo, R. D.: Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years, Quaternary Sci. Rev., 23, 2063–2074, 2004. D'Arrigo, R. D., Kaufmann, R. K., Davi, N., Jacoby, G., Laskowski, C., Mynemi, R. B., and Cherubini, P.: Threshold for warming-induced decline at elevational tree-line in the Yukon Territory, Canada, Global Biochem. Cy., 18, GB3021, doi:10.1029/2004GB002249, 2004. D'Arrigo, R. D., Wilson, R., and Jacoby, G.: On the long-term context for late twentieth century warming, J. Geophys. Res., 111, D03103, doi:10.1029/2005JD006352, 2006. D'Arrigo, R. D., Wilson, R., Liepert, B., and Cherubini P.: On the `Divergence Problem' in Northern Forests: A review of the tree-ring evidence and possible causes, Global Planet. Change, doi:10.1016/j.gloplacha.2007.03.004, 2007. Davi, N., Jacoby, G., and Wiles, G.: Boreal temperature variability inferred from maximum latewood density and tree-ring width data, Wrangell Mt. region, Alaska, Quaternary Res., 60, 252–262, 2003. Driscoll, W., Wiles, G., D'Arrigo, R. D., and Wilmking, M.: Divergent tree growth response to recent climatic warming, Lake Clark National Park and Preserve, Alaska, Geophys. Res. Lett., 32, L20703, doi:10.1029/2005GL024258, 2005. Esper, J., Cook, E., and Schweingruber, F. H.: Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability, Science, 295, 2250–2253, 2002. Fritts, H. C.: Tree Rings and Climate. Academic Press, London, 567 pp, 1976. Goetz, S. J., Bunn, A. G., Fiske, G. J., and Houghton, R. A.: Satellite observed photosynthetic trends across boreal North America associated with climate and fire disturbance, Proceedings of the National Academy of Sciences, 103(38), 13 521–13 525, 2005. Jacoby, G. and D'Arrigo, R. D.: Tree-ring width and density evidence of climatic and potential forest change in Alaska, Global Biogeochem. Cy., 9, 227–234, 1995. Jacoby, G., Lovelius, N., Shumilov, O., Raspopov, O., Kurbainov, J., and Frank, D.: Long-term temperature trends and tree growth in the Taymir region of northern Siberia, Quaternary Res., 53, 312–318, 2000. Lloyd, A. and Fastie, C.: Spatial and temporal variability in the growth and climate response of treeline trees in Alaska, Climatic Change, 52, 481–509, 2002. McBean, G., Alekssev, G. V., Chen, D., et al.: Arctic climate: past and present, in: Arctic Climate Impact Assessment. Cambridge, UK, Cambridge University Press, 21–60, 2005. Mitchell, T. and Jones, P. D.: An improved method of constructing a database of monthly climate observations and associated high-resolution grids, Int. J. Climatol., 25, 693–712, doi:10.1002/joc.1181, 2005. NRC National Research Council: Report on Surface Temperature Reconstructions for the Last 2000 Years, http://nationalacademies.org, 22 June 2006. Pisaric, M., Carey, S., Kokelj, S., and Youngblut, D.: Anomalous 20th century tree growth, MackenzieDelta, Northwest Territories, Canada, Geophys. Res. Lett., 34, L05714, doi:10.1029/2006GL029139, 2007. Wilmking, M., Juday, G. P., Barber, V. A., and Zald, H. S.: Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds, Global Change Biol., 10, 1724–1736, 2004. Wilmking, M. and Juday, G. P.: Longitudinal variation of radial growth at Alaska's northern treeline – recent changes and possible scenarios for the 21st century, Global Planet. Change, doi:10.1016/j.gloplacha.2004.10.017, 2005. Wilmking, M., D'Arrigo, R. D., Jacoby, G., and Juday, G. P.: Divergent growth responses in circumpolar boreal forests, Geophys. Res. Lett., 32, L15715, doi:10.1029/2005GL023331, 2005. Wilmking, M., Harden, J., and Tape, K.: Effect of tree line advance on carbon storage in NW Alaska, J. Geophys. Res., 111, G02023, doi:10.1029/2005JG000074, 2006. Wilson, R. J. S. and Luckman B. H.: Dendroclimatic reconstruction of maximum summer Temperatures from upper treeline sites in Interior British Columbia, Canada, Holocene, 13, 853–863, 2003. Wilson, R. and Elling, W.: Temporal instability in tree-growth/climate response in the Lower Bavarian Forest region: implications for dendroclimatic reconstruction, Trees: Structure and Function, 18, 19–28, 2004. Wilson, R., D'Arrigo, R. D., and Buckley, B.: A matter of divergence: Tracking recent warming at hemispheric scales using tree ring data, J. Geophys. Res., 112, D17103, doi:10.1029/2006JD008318, 2007.