Clonal expansion and seedling recruitment of Oregon grape (Berberis nervosa) in Douglas-fir (Pseudotsuga menziesii) forests: Comparisons with salal (Gaultheria shallon)

Seedling regeneration and morphology of Oregon grape (Berberis nervosa Pursh) and salal (Gaultheria shallon Pursh) were studied in thinned and unthinned Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands in the central Coast Range, Oregon. Above- and below-ground growth of both species were significantly and negatively correlated with stand density. Oregon grape appears to have less potential for vegetative spread than does salal. It produced two to three times fewer rhizome extensions, and rhizome extensions were only half as long as those of salal. Oregon grape seedlings were common in areas of moss ground cover among patches of the two species. Salal seedlings were restricted to decaying logs. Seedling densities of Oregon grape in thinned stands were more than six times those in unthinned stands. For Oregon grape, understory establishment is accomplished by seedling establishment and recruitment of new genets. In contrast, salal maintains itself in forest understories primarily through vegetative growth, since its seedling establishment is restricted mainly to decayed wood. Continual recruitment of new aerial stems or ramets enables Oregon grape to maintain a dense cover once it is established in the understory.