Dynamic effects of insect herbivory and climate on tundra shrub growth:
roles of browsing and ramet age
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.