PARENT SESSION
Oral Session #2: Riparian Ecology.
Presiding: M. Dixon
Monday, August 5. 8:00 AM to 11:30 AM. Greenlee Meeting Room, TCC.

The extent of Salix exigua clones in two California riparian zones.

Douhovnikoff, Vladimir^*,1, ¹ University of California, Berkeley, Berkeley, California

ABSTRACT- Willows play a central role in the ecological function of California's riparian ecosystems. They are known to reproduce by seed and by clonal growth. However, little is known about the relative importance of these two modes of site occupation. In this study we used Amplified Fragment Length Polymorphisms (AFLP) to measure the extent of sandbar willow (Salix exigua ) clones on six sites. Three sites were located on the Cosumnes river, a relatively free flowing river with large flood events. The other three sites were located on the Mokolumne river, a dammed river with rare flooding events. On each site as many as 50 samples were taken using a 5 meter spacing grid. On all six sites clones were found to make up a significant part of the willow populations sampled. Due to past difficulties in accurately measuring clones seed reproduction has been emphasized in most models of willow site occupation. However, we found an assumption that each stem represented a single genet would overestimate genet totals by as much as 500%. In some cases a single clone was so large that it could represent as much as 35% of all the samples collected from a site and cover an area of greater than 30 meters in length. As many as 88% of stems sampled were found to be part of a clone with 2 or more stems. Clones on the more disturbed sites were found to be larger, but the difference was not significant. This extensive clonal growth may explain how willows can so readily colonize sites despite the fact that their seeds are so transient in the environment.

KEY WORDS: clone, Salix exigua, AFLP, riparian