Two case studies of 5 ecosystems were used to examine the nitrogen fixation rate of red alder (Alnus rubra Bong.), varnishleaf (Ceanothus velutinus var. laevigatus (Hook.) T. & G.), deerbrush (C. i ntegerrimus H. & A.), and snowbrush (C. velutinus var. velutinus Dougl. Ex Hook). The first case study assayed nitrogen fixation of 2-yearold
red alder at the Alsea Ranger District of the Siuslaw National Forest and at the OSU Field Laboratory, and 58-year-old red alder at the Cascade Head Experimental Forest. Annual nitrogen fixation was 22.8, 17.5, and 50.1 kg/ha/yr for the Alsea site, OSU Field Laboratory, and Cascade Head, respectively. Red alder showed the potential of substantial nitrogen input into the ecosystem at 2 years
and 58 years of age. The second case study assayed nitrogen fixation of three Ceanothus species growing in southwestern Oregon. At the Waters Creek site, 5- to 6-year-old varnishleaf and deerbrush showed similar nitrogen fixing activity. The seasonal pattern of 11-year-old snowbrush at the Windy
Creek site was different from that of the other Ceanothus species at the Waters Creek site. Annual nitrogen fixation was 8.3, 0.3, and 69.4 kg/ha/yr for varnishleaf, deerbrush
and snowbrush, respectively. Eleven-year-old snowbrush at the Windy Creek site supplied a substantial amount of nitrogen to the ecosystem. Following the attack of California tortoise-shell butterfly, and the subsequent
defoliation of snowbrush, annual nitrogen fixation by snowbrush at the Windy Creek site decreased to 34.8 kg/ha/yr. This value was about one half the value for unattacked shrubs. Red alder can be developed as a tool for forest management at an early stage as well as later stages of growth. Ceanothus species can also be used for forest management, especially in dry areas
