Growth of Salix Setchelliana on a Kluane River Point Bar, Yukon Territory, Canada

Abstract

Setchell willow (Salix setchelliana Ball) is a prostrate clonal species, producing vertical shoots (to about 3 dm) from a shallow horizontal root system. Clonal growth, measured by number of shoots, number of branches, and number of catkins per square meter, was greatest at the middle elevations of a point bar stand, approximately 20 m wide. This paper shows that the narrow limits of this population are associated with specific abiotic factors. The Kluane River (Yukon Territory) shows a yearly fluctuation with highest water at the time of maximum glacial melt in mid-August. Willow shoots closest to the channel are inundated for approximately 60% of their growing season; inundation may set the lower limit of clonal growth. Depth of deposited material increased away from the channel, resulting in deeper horizontal root systems. Substrate in the upper zone, farthest from the channel, had the highest percentage of fines and the highest field water content. Several shoots with decomposed bases were found in this zone, suggesting that the upper limit for clonal growth is established by reduced soil aeration. Seedlings were found only in the upper zone. The period of inundation there is minimal; seed dispersal and water recession probably coincide in some years, thus favoring seedling establishment.