Summary

1. Dense swards of aerial shoots ( < 2.5 cm in height) of Carex subspathacea are heavily grazed by lesser snow geese on intertidal flats on the shores of Hudson Bay. This paper describes the morphological changes in plants which account for the greater net primary production when these swards are grazed.
2. Demographic techniques have been used to monitor the births and deaths of leaves and shoots in grazed and ungrazed swards. Between mid June ('spring thaw') and early September 1984 (just prior to 'freeze up'), shoots in grazed plots produced an average of 8.2 new leaves, compared with an average of 5.7 leaves per shoot in ungrazed plots. This difference accounted for the greater net annual primary production in grazed swards.
3. Within season deaths of leaves totalled 8.0 and 5.7 leaves per shoot, respectively, in grazed and ungrazed plots. Life expectancies were as follows: grazed leaves, 33.3 days; ungrazed leaves in grazed plots, 34.2 days; leaves in ungrazed plots 45.1-47.2 days. This indicates a very rapid turnover of leaves in this arctic salt marsh where the growing season is about 110 days. Some leaves produced late in the season survived the winter but died in early summer of the following year.
4. No differences were detected in the number of new shoots in grazed and ungrazed swards, in contrast to a higher significant within season mortality of shoots in grazed plots. Turnover of shoots is very slow compared with leaves. Shoots remain alive beyond one growing season.
5. The geese graze selectively. Only 20% of shoots in grazed plots were removed and only 3% of leaves were removed completely, although between 42% and 56% of leaves were grazed. Meristems are not destroyed and the continuous production of leaves occurs throughout the season.
6. The growth responses of the sedge to grazing are probably dependent on goose faeces which provide a source of soluble nitrogen in the nitrogen deficient habitat.

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