Relation of Previous Timber Stand Age to Nodulation of Ceanothus velutinus

This study tested the hypothesis that nodulation of snowbrush ( Ceanothus velutinus Dougl.) is inversely proportional to the length of time that snowbrush had been absent from the vegetation mosaic. It was found that the nodulation potential of soils supporting snowbrush could be defined by the following equation: 1n N = 5.5001 — 0.0154 t , where N = percent nodulation and t = previous timber stand age, an index of period of absence of snowbrush at the sampling sites. A greenhouse study indicated the existence of two snowbrush ecotypes, one originating in association with ponderosa pine ( Pinus ponderosa Laws) and the other with Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco). The organism responsible for the nodulation of snowbrush was not seed borne.