Flood drift and propagule bank of aquatic macrophytes in a riverine wetland

Abstract

Abstract. Drift of aquatic macrophyte propagules was investigated in a wetland along the River Rhône, during the first flood after the growing season (i.e. in the winter of 1995–1996). Input and output drift were studied at the beginning, around the top, and at the end of the river overflow in the upper reach of a cut‐off channel. The soil propagule bank was sampled along the study area before and after the flood. The amount and composition of viable propagule drift and bank were determined, analysed and compared. Drift densities and richness were on average higher at the outlet of the channel than at the inlet (respectively: 23.2 vs 13.1 viable propagules/100 m3 of water and 8.7 vs 2.6 taxa per sample). Immigrating taxa were mostly in the form of helophyte seeds, whereas numerous resident hydrophyte species left the disturbed area rather as vegetative propagules.Temporal variability in propagule bank structure was weak, and mean bank densities did not change before and after the flood (respectively: 33 047 ± 10 510 vs 35 653 ± 15 070 viable propagules/m2 of ground, including Chara). However, the density of Elodea canadensis significantly increased after the flood while that of Eleocharis acicularis decreased. This contrast suggests that flood responses vary among species. Despite a broad overlap in the taxa (18 out of 25 were common both to drift and bank collections), no significant relationship occurred in composition or structural changes between flood drift and propagule bank. Flood acted as a means of distribution of existing propagules and also as a provider of new vegetative dispersal units.

The dispersal capacity of vegetative propagules of riparian fen species

“…First, high numbers of vegetative propagules are dispersed by hydrochory, especially during the winter months. In rivers, Cellot et al (1998) found that the number of vegetative propagules in the water increased by flooding as greater turbulence caused more fragmentation of aquatic and riparian plants. In the ponds of this study, the increased number of vegetative propagules in autumn and winter can most likely be explained by natural decay of (submerged) macrophytes and the increased turbulence in the water by stronger winds as they were not dredged.…”

Relationship between seed and clonal growth in the reproduction of Carex rugulosa Kük. in riverside meadows

“…Vegetative organs, such as floating turions or the shoot fragments of some aquatic plants and tideland halophytes, are known to be able to contribute as colonizers (Grace 1993;Sanchez et al 2001;Capers 2003). Even rhizomes and subterranean tubers of riparian species can be dispersed, particularly in the case of floods (Cellot et al 1998;Khudamrongsawat et al 2004;Decruyenaere & Holt 2005;Minchinton 2006). However, we have never seen floating plant parts of C. rugulosa at our study site, whereas drifting reed fragments, Phragmites australis, are fairly common in the Ohashi River estuary (S. Araki & H. Kunii, pers.…”

Effects of an enhanced flood on riparian plants of the River Murray, South Australia

“…Increased depth would promote flood-tolerant species higher on the elevation gradient, and increased duration would promote clonal growth and the production and dispersal of propagules by flood-tolerant and aquatic plants (cf. Cellot et al, 1998). This will increase the time available for plants like E. acuta to spread via clonal growth.…”