The biomass and the composition of 15 stands of red alder (Alnus rubra Bong.) on river bottom sites in western Oregon was measured during August and early September, 1969. These stands ranged in age from two to 64 years. Biomass was found to vary from 134 k/ha (kilograms per hectare) for the very youngest stand to 7700 k/ha in one of the older stands. Net productivity for the first 64 years was estimated as 97 k/ha per year. Understory biomass was found to be a very small portion, up to Z. 5%, of the biomass of the alder overstory for similar stands. Composition was found to vary considerably as age of the overstory increased. Succession from a. grass-herb dominated understory to a shrub-fern dominated understory was quantified. The findings appear to support an earlier prediction that lands now dominated by reda1der may be dominated by brush fie1ds of Rubus spectailis in the future n the absence of a suitable conifer seed source.