Invasion of Norway spruce diversifies the fire regime in boreal European forests

Authors

  • Mikael Ohlson,

    Corresponding author
    1. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, NO-1432 Ås, Norway
      Correspondence author. E-mail: mikael.ohlson@umb.no
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  • Kendrick J. Brown,

    1. Geological Survey of Denmark and Greenland – GEUS, Ø. Voldgade 10, DK-1350 Copenhagen K, Denmark and Canadian Forest Service, Northern Forestry Centre, 5320 – 122nd Street, Edmonton AB T6H 3S5, Canada
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  • H. John B. Birks,

    1. Department of Biology, University of Bergen, PO Box 7803, NO-5020 Bergen, Norway
    2. Bjerknes Centre for Climate Research, University of Bergen, NO-5007 Bergen, Norway and School of Geography and the Environment, University of Oxford, Oxford OX1 3QY, UK
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  • John-Arvid Grytnes,

    1. Department of Biology, University of Bergen, PO Box 7803, NO-5020 Bergen, Norway
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  • Greger Hörnberg,

    1. The Institute for Subarctic Landscape Research, SE-930 90 Arjeplog, Sweden
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  • Mats Niklasson,

    1. Southern Swedish Forest Research Centre, PO Box 49, SE-230 53 Alnarp, Sweden
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  • Heikki Seppä,

    1. Department of Geosciences and Geography, University of Helsinki, PO Box 64, FI-00014 Helsinki, Finland
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  • Richard H. W. Bradshaw

    1. Department of Geography, University of Liverpool, Roxby Building, Liverpool L69 7ZT, UK
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Correspondence author. E-mail: mikael.ohlson@umb.no

Summary

1. Global wildfire activity and biomass burning have varied substantially during the Holocene in both time and space. At the regional to continental scale, macroclimate is considered to be the predominant control regulating wildfire activity. By contrast, the role of forest tree composition is often considered as a subsidiary factor in studies addressing temporal variation in regional wildfire activity.

2. Here, we assemble a spatially comprehensive data set of 75 macroscopic charcoal records that reflect local burning and forest landscapes that are spread over a substantial part of the European boreal forest, spanning both oceanic and continental climates.

3. We show that the late-Holocene invasion of Norway spruce Picea abies, a new forest dominant in northern Europe, significantly reduced wildfire activity, thus altering forest disturbance dynamics at a subcontinental scale.

4.Synthesis. Our findings show that a biotic change in the local forest ecosystem altered the fire regime largely independent of regional climate change, illustrating that forest composition is an important parameter that must be considered when modelling future fire risk and carbon dynamics in boreal forests.

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