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The influence of sampling design on tree-ring-based quantification of forest growth

Authors

  • Christoph Nehrbass-Ahles,

    Corresponding author
    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
    • Correspondence: Present address: Christoph Nehrbass-Ahles, Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, Bern CH-3012, Switzerland and Oeschger Centre for Climate Change Research, University of Bern, Zähringerstrasse 25, Bern CH-3012, Switzerland, tel. +41 31 631 4466, fax +41 31 631 8742, e-mail: nehrbass@climate.unibe.ch; David Frank, tel. +41 44 7392 282, fax +41 44 7392 215, e-mail: david.frank@wsl.ch

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  • Flurin Babst,

    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
    2. Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ, USA
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  • Stefan Klesse,

    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
    2. Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
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  • Magdalena Nötzli,

    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
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  • Olivier Bouriaud,

    1. National Forest Inventory, Forest Research and Management Institute, ICAS, Voluntari, Romania
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  • Raphael Neukom,

    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
    2. Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
    3. Department of Geography, University of Zurich, Zurich, Switzerland
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  • Matthias Dobbertin,

    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
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  • David Frank

    Corresponding author
    1. Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
    2. Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
    • Correspondence: Present address: Christoph Nehrbass-Ahles, Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, Bern CH-3012, Switzerland and Oeschger Centre for Climate Change Research, University of Bern, Zähringerstrasse 25, Bern CH-3012, Switzerland, tel. +41 31 631 4466, fax +41 31 631 8742, e-mail: nehrbass@climate.unibe.ch; David Frank, tel. +41 44 7392 282, fax +41 44 7392 215, e-mail: david.frank@wsl.ch

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Abstract

Tree-rings offer one of the few possibilities to empirically quantify and reconstruct forest growth dynamics over years to millennia. Contemporaneously with the growing scientific community employing tree-ring parameters, recent research has suggested that commonly applied sampling designs (i.e. how and which trees are selected for dendrochronological sampling) may introduce considerable biases in quantifications of forest responses to environmental change. To date, a systematic assessment of the consequences of sampling design on dendroecological and-climatological conclusions has not yet been performed. Here, we investigate potential biases by sampling a large population of trees and replicating diverse sampling designs. This is achieved by retroactively subsetting the population and specifically testing for biases emerging for climate reconstruction, growth response to climate variability, long-term growth trends, and quantification of forest productivity. We find that commonly applied sampling designs can impart systematic biases of varying magnitude to any type of tree-ring-based investigations, independent of the total number of samples considered. Quantifications of forest growth and productivity are particularly susceptible to biases, whereas growth responses to short-term climate variability are less affected by the choice of sampling design. The world's most frequently applied sampling design, focusing on dominant trees only, can bias absolute growth rates by up to 459% and trends in excess of 200%. Our findings challenge paradigms, where a subset of samples is typically considered to be representative for the entire population. The only two sampling strategies meeting the requirements for all types of investigations are the (i) sampling of all individuals within a fixed area; and (ii) fully randomized selection of trees. This result advertises the consistent implementation of a widely applicable sampling design to simultaneously reduce uncertainties in tree-ring-based quantifications of forest growth and increase the comparability of datasets beyond individual studies, investigators, laboratories, and geographical boundaries.

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