, Volume 16, Issue 4, pp 561–575 | Cite as

Ecosystem Impacts of a Range Expanding Forest Defoliator at the Forest-Tundra Ecotone

  • Jane U. Jepsen
  • Martin Biuw
  • Rolf A. Ims
  • Lauri Kapari
  • Tino Schott
  • Ole Petter L. Vindstad
  • Snorre B. Hagen


Insect outbreaks in northern-boreal forests are expected to intensify owing to climate warming, but our understanding of direct and cascading impacts of insect outbreaks on forest ecosystem functioning is deficient. The duration and severity of outbreaks by geometrid moths in northern Fennoscandian mountain birch forests have been shown to be accentuated by a recent climate-mediated range expansion, in particular of winter moth (Operophtera brumata). Here, we assess the effect of moth outbreak severity, quantified from satellite-based defoliation maps, on the state of understory vegetation and the abundance of key vertebrate herbivores in mountain birch forest in northern Norway. We show that the most recent moth outbreak caused a regional-scale state change to the understory vegetation, mainly due to a shift in dominance from the allelopathic and unpalatable dwarf-shrub Empetrum nigrum to the productive and palatable grass Avenella flexuosa. Both these central understory plant species responded significantly and nonlinearly to increasing outbreak severity. We further provide evidence that the effects of the outbreak on understory vegetation cascaded to cause strong but opposite impacts on the abundance of the two most common herbivore groups. Rodents increased with defoliation, largely mirroring the increase in A. flexuosa, whereas ungulate abundance instead showed a decreasing trend. Our analyses also suggest that the response of understory vegetation to defoliation may depend on the initial state of the forest, with poorer forest types potentially allowing stronger responses to defoliation.


insect outbreak sub-arctic birch forest Operophtera brumata Epirrita autumnata geometrids vegetation state transitions Empetrumnigrum Avenella flexuosa reindeer Tundra vole 



We thank Kristoffer Juell, Saga Svavarsdottir, and Stein-Rune Karlsen for assistance during field work. René van der Wal and one anonymous reviewer provided valuable suggestions for improvements on an earlier draft of the manuscript. Financial support was obtained from the Research Council of Norway, and supplementary support from the University of Tromsø, the Norwegian Institute for Nature Research and Bioforsk Svanhovd, Norway. This study is an activity under the Nordic Centre of Excellence “How to preserve the tundra in a warming climate (NCoE-Tundra).”

Supplementary material

10021_2012_9629_MOESM1_ESM.pdf (147 kb)
Supplementary material 1 (PDF 148 kb)


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Copyright information

© Springer Science+Business Media New York 2012

Authors and Affiliations

  • Jane U. Jepsen
    • 1
  • Martin Biuw
    • 1
  • Rolf A. Ims
    • 2
  • Lauri Kapari
    • 2
  • Tino Schott
    • 2
  • Ole Petter L. Vindstad
    • 2
  • Snorre B. Hagen
    • 3
  1. 1.Norwegian Institute for Nature Research (NINA)TromsøNorway
  2. 2.Department of Arctic and Marine BiologyUniversity of TromsøTromsøNorway
  3. 3.Bioforsk, Norwegian Institute for Environmental and Agricultural ResearchSvanvikNorway

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