Evidence for hydrochory and the deposition of viable seeds within winter flow-deposited sediments: the River Dove, Derbyshire, UK

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Abstract

Previous studies of the influence of hydrochory on plant dispersal have focused on relationships with existing vegetation patterns or litter deposits. River sediment deposition studies have assessed sediment accretion rates, particle size and quality. The link between seed and sediment transport and deposition has been overlooked and never quantified.

This paper presents observations of over-winter viable seed and sediment deposition on three river margin sites along the River Dove, England. At these sites, 105 paired artificial turf mats were installed on the river bank top, face and toe from October 1999 to March 2000 to collect river-deposited material. From each pair, one mat was used to determine the dry weight; median particle size; percentage sand, silt, clay and organic content of deposited sediment. The other was used in germination trials to determine the number and species of deposited viable seeds. Topographic surveys and water level measurements supported the estimation of the hydrological characteristics of each mat location.

Few seeds and little sediment were found on mats not inundated by river water. For these inundated, sediment characteristics varied primarily with elevation (relative to local mean river water level during the study period), with less marked between-site contrasts. The species composition of viable seeds also varied with elevation. Detrended correspondence analysis (DCA) revealed associations between river/wetland-related seed species and the bank toe samples. Regression analysis revealed significant relationships between seed number, sediment properties and mat elevation. Redundancy analysis (RDA) revealed associations between the species and abundance of viable seeds and elevation, sediment weight and organic matter content. These analyses suggest that sediment and seed deposition by rivers are closely related processes.

The implications of these results for seed remobilization and dispersal and hydrochory within riparian zones are discussed, as are the implications of changes in sediment/seed delivery mechanisms, river flow regimes, and the hydraulic properties of river margins for seeds, sediments and riparian vegetation patterns. Copyright © 2003 John Wiley & Sons, Ltd.

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