Leaf and Shoot Demography of an Arctic Stoloniferous Grass, Puccinellia Phryganodes, in Response to Grazing

Abstract

(1) Swards ( < 2 5 cm in height) of Puccinellia phryganodes are heavily grazed by lesser snow geese (Chen caerulescens caerulescens) on intertidal flats on the shores of Hudson Bay. This paper describes the morphological changes that account for the increased net primary production due to grazing. (2) Demographic techniques were used in 1983 to monitor the births and deaths of leaves and shoots in grazed and ungrazed swards (exclosures) between mid-June ('spring melt') and early September (before 'freeze-up'). (3) Overall, the mean number of axillary shoots produced per main shoot of Puccinellia was significantly higher in grazed plots (2 03) than that in ungrazed plots (1 47). Shoots remained alive beyond one growing season. (4) There was no significant difference in the mean number of leaves produced per main shoot by plants from grazed and ungrazed swards. Leaf births per axillary shoot were significantly greater in grazed plots compared with ungrazed plots. Overall 64% of all leaves produced between June and September were grazed or partially grazed. (5) Within-season cumulative deaths were 6 9 and 6 0 leaves per main shoot and 2 2 and 1 1 leaves per axillary shoot, respectively, in grazed and ungrazed plots. Life expectancies for leaves exserted between June and early August were as follows: partially grazed leaves 24 9-30 2 days, ungrazed leaves in grazed plots 27 5-34 4 days, leaves in ungrazed plots 32 7-42 5 days. This indicates a rapid turnover of leaves in this arctic salt marsh. Leaves produced late in the season survived the winter but died in early summer of the following year. (6) These results are compared with those of Carex subspathacea, the other important forage species. In C. subspathacea the greater net primary production in response to grazing is achieved by the growth of existing shoots and not by the production of new shoots.