Controls on the sexual and asexual regeneration of Salicaceae along a highly dynamic, braided river system |
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Authors: | Helen L Moggridge Angela M Gurnell |
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Institution: | 1. Department of Geography, King’s College London, Strand, London, WC2R 2LS, United Kingdom
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Abstract: | Salicaceae are key pioneer riparian tree species that have the ability to reproduce sexually and asexually. Recent research
has suggested that Salicaceae act as ‘ecosystem engineers’, modifying hydrological and geomorphological processes, resulting
in the stabilisation and growth of landforms. Understanding these interactions requires knowledge of the controls on Salicaceae
regeneration. This paper describes a study of Salicaceae establishment and growth along a reach of a highly dynamic, island-braided
river. The sexual and asexual regeneration of three species were investigated using experimental planting of cuttings and
observation of seedlings. Plots were located at a range of elevations, in different habitats associated with the established
riparian vegetation and in contrasting sediment types. Survival and growth were monitored over two growing seasons. Asexual
regeneration was more successful than sexual regeneration, with cuttings demonstrating faster growth rates and tolerance of
broader environmental conditions than seedlings. Cutting survival and growth was highest in sediments with a relatively high
organic content and in plots located between patchy Salicaceae stands or in the lee of islands. Seedling mortality was extremely
high due to fluvial disturbance, although seedlings in habitats that were protected from fluvial disturbance survived. Seedling
growth showed preferences for particular sedimentary conditions, which varied between species. The major control on regeneration
was the upstream presence of established Salicaceae, particularly on islands, which provided open sites that were protected
from fluvial disturbance and suitable for regeneration. Thus, asexual regeneration facilitated sexual regeneration by rapidly
colonising sites that provided habitats protected from fluvial disturbance for seedling establishment. This supports previous
work suggesting that Salicaceae can act as ‘ecosystem engineers’. |
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