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We investigated the role of lemming herbivory on the age structure and physical form of a stand of willows (Salix lanata) using lemming scars on stems as an indication of past herbivory. Salix lanata had a female-biased sex ratio comparable to that found in other willow species and it has been proposed that such a sex ratio may be due to selective herbivory on male genets. There was, however, no difference in the degree of scarring in male and female plants. Scarring did not appear to change the overall physical structure of the willows including the number of stems, the proportion of dead steams and the degree of branching. However, 72% of scarred 7 mm stems were dead, compared to only 22% of non-scarred stems, suggesting that lemming herbivory may play a role in ramet death. There was a significant positive correlation between stem ages and the lemming cycle as determined by the frequency of scars. With experimental scarring, S. lanata increased its production of new shoots in relation to the degree of scarring. We suggest that this demonstrates a pattern of compensatory growth in willows, whereby they take advantage of a period of relatively low herbivory following the crash of the lemming populations in order to compensate for damage that occurred during the lemming peak.
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