Growth response of Betula pubescens Ehrh. to varying disturbance factors in northern Norway
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ORIGINAL ARTICLE
Growth response of Betula pubescens Ehrh. to varying disturbance factors in northern Norway Lorenz Harr1 · Jan Esper1 · J. Andreas Kirchhefer2 · Wang Zhou1,3,4,5,6 · Claudia Hartl1 Received: 17 April 2020 / Accepted: 25 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Key message Whereas cold temperatures and artificial smoke pollution (during World War II) cause negative pointer years in northern Fennoscandian downy birches, mass outbreaks of Epirrita autumnata L. and Operophtera brumata Bkh. are the strongest growth-influencing and -synchronizing factor. Abstract Variations in radial tree growth of downy birch can be affected by short-term environmental changes. Here we examine the tree-ring width of downy birch trees for signals caused by three different disturbance factors: climatic extremes, insect outbreaks, and artificial smoke employed to hide the German battleship Tirpitz during World War II at the Kåfjord in northern Norway. Besides growth/climate response analysis using gridded climate data and a tree ring width-chronology of the studied birch trees, we analyze missing rings, pointer years, and the ability of recovery after severe disturbances on an individual tree basis using the percent change of the trees’ basal area increment with respect to a reference period. The downy birches reveal (1) a significant positive correlation with May and June temperatures, (2) a high growth sensitivity to moth epidemics (Epirrita autumnata L. and Operophtera brumata Bkh.), and (3) a distinct growth deviation in the year of intense but short-term artificial smoke pollution. We conclude that downy birches are not exclusively sensitive to unusual cold temperatures, but short-term artificial pollution and insect outbreaks cause similar growth declines in the year of occurrence. Whereas for temperature and pollution, the growth response is less coherent among trees, and fades within 2 years, the insect outbreaks synchronize growth among all downy birches. Growth declines during years of mass insect outbreaks can further be amplified by cold May and June temperatures. Our findings thereby improve the understanding of competing disturbance factors on single birch trees but also on the growth of a whole site in Fennoscandia and facilitates the detection of disturbances in birch chronologies. Keywords Downy birch · Smoke screens · Moth outbreaks · Climate extremes · Tree rings · Dendroecology
Introduction Communicated by Piovesan. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00468-020-02043-1) contains supplementary material, which is available to authorized users. * Lorenz Harr [email protected]‑mainz.de 1
Department of Geography, Johannes Gutenberg-University, Johann‑Joachim‑Becher‑Weg 21, 55128 Mainz, Germany
2
Dendroøkologen, Skogåsvegen 6, 9011 Tromsö, Norway
3
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, 723
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