Riparian tree establishment on gravel bars: interactions between plant growth strategy and the physical environment

Robert Francis, Angela Gurnell, Geoff E. Petts, Peter J. Edwards

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

This paper investigates the influence of propagule form (seedlings, vegetative fragments and living drift-wood) and the physical environment (relative elevation and sediment calibre of the location of deposition) on the establishment of two pioneer riparian tree species, Populus nigra L. and Salix elaeagnos Scop. Field observations suggest that vegetative reproduction by these species is a key process in the establishment of vegetation on bar surfaces, and also the formation of wooded islands. In a field experiment conducted along the braided Tagliamento River, Italy, during the 2002 growing season, cuttings of the two species were established in locations representing differing combinations of relative elevation (depth to water table) and sediment calibre. Survival and growth
parameters were measured both during and at the end of the growing season. Measurements of seedling growth and photomonitoring of stem growth from living wood debris were also undertaken.

Initial results indicate that cuttings and seedlings of both species respond differently to combinations of elevation and sediment calibre, with cuttings performing best at lower elevations but showing no consistent preference for sediment calibre, while seedlings perform best at higher elevations and show a preference for either coarse (S. elaeagnos) or fine sediments (P. nigra). Of the
two environmental parameters, elevation may have a greater importance for survival and growth of P. nigra, while sediment calibre may be the key variable for S. elaeagnos. Analysis of stem lengths from the various propagules suggests that growth rates can be substantially higher among fluvially deposited trees, followed by cuttings and then seedlings. Therefore, the topographical and sedimentary characteristics of bar formations in relation to propagule type and species deposited can exert a substantial influence upon vegetation establishment and, consequently, subsequent patterns and rates of sedimentation. This in turn may have a considerable impact on island development and river morphology.
Original languageEnglish
Title of host publicationBraided Rivers: Process, Deposits, Ecology and Management
Place of PublicationMalden, MA
PublisherWILEY-BLACKWELL
Pages361-380
Number of pages20
ISBN (Electronic)9781444304374
ISBN (Print)9781405151214
Publication statusPublished - 2006

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