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Dynamic effects of insect herbivory and climate on tundra shrub growth: roles of browsing and ramet age
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  • Risto Virtanen,
  • Adam Clark,
  • Michael den Herder,
  • Heikki Roininen
Risto Virtanen
University of Oulu
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Adam Clark
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig
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Michael den Herder
European Forest Institute
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Heikki Roininen
University of Eastern Finland
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Abstract

To predict plant responses under climate change, we need to understand how thermal conditions and herbivory contribute to shoot growth. Here, we used empirical dynamic modelling (EDM) to analyse an 18-year time series from an experimental system at the forest-tundra ecotone to identify relationships between growth, climate, insect herbivores, browsers and ramet age. We found that negative effects of insect herbivory on willow shoot growth are intensified during warmer years. Moreover, the negative effect of insect herbivores was moderated by ramet age, but this moderation was only realized in the absence of vertebrate herbivores – under browsing by both ptarmigans and reindeer, the positive effects of ramet age were eliminated. Jointly, these results demonstrate the context-dependent and dynamic effects of climate and multiple herbivores on shoot growth, and improve our ability to predict effects of climatic warming in arctic environments.