Clonal growth of Salix setchelliana on glacial river gravel bars in Alaska

(1) Salix setchelliana is a prostrate clonal willow that grows peripherally from a horizontal root system. Vertical shoots are typically 5-20 cm tall. The growth and demography of shoots and clones have been examined in Denali National Park, Alaska, and have been related to the transitory gravel bar habitat. (2) Shoot emergence and death rates, measured along two river systems, did not show significant year to year variability, but were affected by position within a clone. Shoot death, but not shoot emergence, differed between the patches sampled. Shoot survivorship curves are log linear. (3) Patch survivorship, measured in one river system, averaged 95% per year. Clonal expansion rates averaged 0.25 and 0.19 m year-1at the two locations examined. Clones vary in their percentage of expanding versus non-expanding edges; the non-expanding edges are associated with old channel banks or gravel with large rocks and large shrubs. Clonal segments broken off by migrating river channels appear to be able to serve as long-distance propagules. (4) S. setchelliana exhibits rapid radial spread, reducing the likelihood of genet extinction in its transitory habitat.