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1 April 2017 Linking Seedling Spatial Patterns To Seed Dispersal Processes In An Intermittent Stream
John M. Boland
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To better understand the colonization of bare riparian sites, I examined seedling distribution patterns and seed dispersal processes of 11 common riparian species. The study site was two in-channel sedimentation basins on an intermittent stream flowing into the Tijuana River Valley, southern California. The 11 species relied on one of two vectors to disperse seeds into the basins, either water or wind. Seven species dispersed to the basins via winter stream flows and, of these, three grew mainly at the basin periphery and four grew mainly in the bed. Seed buoyancy tests and tests of dispersal using seed mimics showed that, for these species, the main process producing seedling distributions was that of sorting of the seeds by the stream flows based on seed buoyancy. Most past work on seed dispersal in riparian habitats has been conducted in perennial systems where non-buoyant seeds usually remain in deep water and never germinate, and this has led to the notion that non-buoyant seeds are not effectively dispersed by water. This study shows that non-buoyant seeds are effectively dispersed by flows in intermittent systems because the seeds were able to germinate and grow once the bed had dried. Four species dispersed to the basins via wind, and their seedlings grew in concentric bands around the basins. Monitoring of seed production and tracking of the basin's water level showed that, for these species, seedling distributions were the result of staggered periods of seed dispersal and gradual decline of the water level. Only three of these 11 species were abundant in the five- and 22-year old stands examined, i.e., the wind-dispersed Baccharis salicifolia (Ruiz & Pav.) Pers., Salix lasiolepis Benth., and S. gooddingii C.R. Ball. A banding pattern established at the time of recruitment, with S. lasiolepis higher on the bank than S. gooddingii, was retained in the older forests, making this one of very few examples that show a direct link between seed dispersal processes, seedling distributions, and adult distributions. This study provides insight into the early development of riparian woodlands by identifying and explaining distribution patterns in water- and wind-dispersed colonizers.

John M. Boland "Linking Seedling Spatial Patterns To Seed Dispersal Processes In An Intermittent Stream," Madroño 64(2), 61-70, (1 April 2017).
Published: 1 April 2017
natural restoration
seed buoyancy
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