The impact of litter and annual plants on recruitment from the seed bank of a lacustrine wetland

Abstract

In an experimental marsh complex, 2 years of high water (1 m above normal) killed most of the emergent vegetation. During 1983, the first year of a 2-year drawdown, immediately following this period of high water, field experiments involving the removal of fallen emergent, filamentous algal and mixed (algal and emergent) litter were established at 6, 4 and 7 sites, respectively. All three indicated that the removal of litter significantly increased the number of species and the number of individuals of a species recruited from the seed bank. During 1984, the number of species and number of individuals in the removal treatment at emergent- and mixed-litter sites was again significantly higher than in the controls, but there was no longer a difference at algal litter sites. The addition of a mat of Typha litter in June 1983, at five sites that were free of litter, reduced seedling recruitment from the seed bank almost completely in both 1983 and 1984. The removal of 1982-standing litter, from sites at higher elevations that were invaded by Typha or Phragmites during the high water period, also increased the number of species and the number of individuals of a species compared with the controls in 1983. Removal of seedlings of the mudflat annual, Atriplex patula L., increased the number of grass shoots significantly in both 1983 and 1984. Grasses in the seedling removal treatment were also taller and flowered in 1983, the first year of the drawdown.