Salmonberry clonal and population structure: the basis for a persistent cover

To understand how populations of salmonberry (Rubus spectabilis) persist in common forest stand types, we studied the above- and belowground structure of salmonberry clones and populations in upland alder and conifer stands, in riparian stands, and in 2-yr-old and 13- to 18-yr-old clearcuts in the central Oregon Coast Range. On undisturbed sites individual clones and populations replace aerial stems by rhizome extension, by production of new genets, and by sprouts from buds on old aerial stems. It appears that frequent initiation of aerial stems from these three sources enables salmonberry populations to persist and maintain a dense cover. The size distribution of aerial stems on these sites resembled that of an uneven-aged stand of trees, with stem numbers decreasing from small to large size classes. Within the first two growing seasons after disturbance to overstory trees and the understory, salmonberry populations maintained themselves by a rapid initiation of new rhizomes (1.0-2.5 m/[m.sup.2] annually) and aerial stems (25-50 stems/[m.sup.2]). These populations apparently continue to grow well, since the greatest rhizome and aerial stem biomass occurred in 13- to 18-yr-old clearcuts with no overstory trees. Rhizome density of salmonberry populations, as well as rhizome and aerial stem biomass, was significantly and negatively related ([r.sup.2] = 0.71-0.83) to the basal area of overstory trees. It appears that population structure, rhizome length and aerial stem, rhizome, and total biomass, can be predicted from measures of preharvest overstory trees, and also from salmonberry stem number and basal area. Clonal architecture varied with stand type. Salmonberry clones in alder stands were larger (18 m total rhizome) than those in conifer stands and on riparian sites (5-6 m rhizome). Clones in alder stands also produced more ramets and more aerial stems than those in conifer and riparian stands.