SEED FLOATING ABILITY AND DISTRIBUTION OF ALPINE PLANTS ALONG A NORTHERN SWEDISH RIVER

In this study we tested the hypothesis that diaspore buoyancy is an im portant factor in determining the distribution range of riparian plant s, by measuring the floating capacity of fruits and seeds from 17 alpi ne vascular plant species during 1 yr. Minimum, median, mean, and maxi mum (less than or equal to 1 yr) floating times of fruits and seeds we re then related to the downstream distribution of plants along the fre e-flowing Vindel River in northern Sweden. The distances from the alpi ne headwater region to the most downstream occurrence of plants, and t o the cessation of a more continuous distribution, were evaluated. The variation in downstream limits of plants could not be statistically e xplained by variation in seed buoyancy between species, indicating tha t floating ability of seeds is not important for plant distribution pa tterns. There may be several reasons for this, and they may differ bet ween species.