INTRA‐INDIVIDUAL PLANT RESPONSE TO MOOSE BROWSING: FEEDBACK LOOPS AND IMPACTS ON MULTIPLE CONSUMERS

Abstract

Salix phylicifolia responds to moose browsing with an intra‐individual plant response. This plant–animal system is characterized by complex changes in plant chemistry and plant morphology which in turn lead to differences in feeding strategies of future consumers.I postulate that the willow Salix phylicifolia has developed a two‐level strategy which results in two different types of twigs (new annual shoots) after moose browsing in winter. This strategy enables the plant to protect reproductive organs by offering two chemically different twigs to herbivores, with catkins concentrated on the less preferred twigs. In addition, it may enable plants to grow out of the reach of browsers. New growth of browsed and unbrowsed twigs on the same individual willow differed in morphology and chemical composition (intra‐individual response). New growth from browsed twigs had lower concentrations of individual phenolics, a higher biomass (twigs and leaves), and lower concentrations of nitrogen in leaves than the new growth of unbrowsed twigs. This response resulted in a positive feedback loop for moose, which typically rebrowsed the new growth of browsed twigs, whereas the new growth of unbrowsed twigs was avoided. This feeding behavior was consistent for leaf stripping by moose in summer and pruning of twigs in winter. I found no differences in the feeding behavior of herbivorous insects on the leaves growing on the new annual shoots of either browsed or unbrowsed twigs. The new growth of unbrowsed twigs, which were protected by different specific phenolics, had more catkins than the new growth of browsed twigs. In an interindividual comparison, the number of catkins on browsed willows was reduced. Hence, browsing has an impact on willow reproduction and pollinators. Consequently, large herbivores such as moose are likely to be a driving force in shaping patterns of plant response and plant and consumer communities.