Seed rain and seed bank of third- and fifth-order streams on the western slope of the Cascade Range.

Abstract

We compared the composition and density of the on-site vegetation, seed bank, and seed rain of three geomorphic and successional surfaces along third- and fifth-order streams on the western slope of the central Cascade Range in Oregon.

The on-site vegetation generally was dominated by tree species, the seed bank by herb species, and the seed rain by tree and herb species. Seed rain density generally corresponded to the successional stage of the geomorphic surface and frequency of site disturbance, with the youngest and least vegetatively stable geomorphic surfaces having the highest density of trapped viable seeds. The highest density and greatest species richness of seed bank germinants were found on the intermediate-aged geomorphic surfaces, which had moderate levels of disturbance. In comparison, the younger and older geomorphic surfaces (with greater and lesser disturbance levels than the intermediate-aged surfaces, respectively) had equal but lower seed bank densities. The seed banks of the youngest, least stable geomorphic surfaces, however, were substantially richer in species than those of the oldest, most vegetatively stable surfaces.

A large and diverse array of plant propagules, provided by both seed rain and seed banks, are available to riparian sites in forests in the Pacific Northwest. Many of the propagules represent species currently absent from the aboveground vegetation on these sites.

Citation

Harmon, Janice M.; Franklin, Jerry F. 1991. Seed rain and seed bank of third- and fifth-order streams on the western slope of the Cascade Range. Res. Pap. PNW-RP-480. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 27 p