Abstract

Seasonal germination from the seed banks of five wetlands that experience unpredictable fluctuations in water level was examined by wetting dried sediments at three-monthly intervals over a 14-month penod. Germination trials were conducted both outdoors and in an unheated, naturally lit glasshouse. In each trial, sediments were maintained in a waterlogged condition for eight weeks, after which all germinating individuals were counted and identified. Although germination occurred in all seasons at all sites, both numbers of species and numbers of individuals germinating from the wetted sediments were significantly affected by season, both outdoors and in the glasshouse. In the outdoor trials, greatest numbers of individuals and species generally appeared in autumn, fewest in summer. Sensitivity to a combination of high maximum and high mlnimum temperatures may have evolved in wetland species of the area as a mechanism ensuring that germination is dramatically reduced in summer, when conditions for establishment of young seedlings may be particularly unfavourable.