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The Seed Regeneration Dynamics of an Emergent Salt Marsh

M. J. Hutchings and P. J. Russell
Journal of Ecology
Vol. 77, No. 3 (Sep., 1989), pp. 615-637
DOI: 10.2307/2260974
Stable URL: http://www.jstor.org/stable/2260974
Page Count: 23
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The Seed Regeneration Dynamics of an Emergent Salt Marsh
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Abstract

(1) The dynamics of the seed-regeneration phase were investigated for several halophyte species at three elevations on an emergent salt marsh. For each species at each site, the number of seeds produced, seed viability, the number of seeds appearing in the soil seed bank, germination from the seed bank and seedling survival were documented. Flow charts are presented illustrating the fates of seeds and seedlings during the process of regeneration, and similarity coefficients are calculated between the composition of the vegetation growing on the sites and the composition of the seed or seedling population at each of several stages during regeneration. (2) No seed production was recorded for several species occurring in the established vegetation of the three sites. The greatest seed output on the high site was by Juncus gerardi, the seventh most abundant species in the vegetation. On the middle site, highest seed output was by Plantago maritima, the second most abundant species in the vegetation. On the low site, the most abundant species, Puccinellia maritima, had the greatest seed output. Total seed output ranged from 20 000 m-2 on the high site to 11 000 m-2 on the low site. (3) Viability of seeds produced by most species was over 80%. There were marked differences in the timing of ripe seed production by different species. A higher proportion of the seed output appeared in the seed bank for species with seeds ripening in summer than for those with seeds ripening in autumn. (4) Large numbers of seeds were recovered from the soil for six species. These included Urtica dioica, which did not grow on the marsh. Apart from Puccinellia maritima on the low site, all the halophytes that were efficiently sampled had transient seed banks on all sites. All were Type II (spring germinating), except for Puccinellia maritima on the high and middle sites and Armeria maritima. These had transient Type I (winter germinating) seed banks. Three small-seeded species (J. gerardi, Inula crithmoides and Spergularia marina) were not efficiently sampled from the soil; they are more likely to have persistent seed banks. The maximum seed bank size was 4.4 times greater on the low site than on the high site. (5) Generally, species showed their highest levels of germination and seedling survival on sites where they had their highest percentage cover and seed production. Germination from the seed bank was greater for species with high seed-production rates. Seedling survival until the end of the study was low except for Aster tripolium and I. crithmoides on the high site and for the annual Suaeda maritima on the low site. (6) There was a strong correspondence between the composition of the growing vegetation and the seed bank on all sites. This is because the seed banks are not persistent and therefore reflect the seed output of the current vegetation rather than that of the vegetation growing at some time in the past, as in most plant communities dominated by perennial species. The seed banks were dominated by seeds of perennial species. The similarity between the different stages in the process of regeneration was greatest for the low site, where the vegetation, and all steps in the regeneration process, contained a higher proportion of annual species. (7) There was far greater loss of seeds and seedlings on the high marsh site at each stage in regeneration than on the lower sites.

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