RESPONSE TO FIRE OF CEANOTHUS RODERICKII (RHAMNACEAE), A FEDERALLY ENDANGERED CALIFORNIA ENDEMIC SHRUB

Abstract

Experimental burns involving rare plants can provide important information for managers of those species. This study examined the response to prescribed fire of Ceanothus roderickii, a federally endangered chaparral species endemic to gabbro soils of the Pine Hill Formation in western El Dorado County, California. I conducted a laboratory study of germination cues, a field comparison of germination and survival on burned and unburned plots, and a comparison of seedling survival in burned plot subplots that were protected from vertebrate herbivores by wire exclosures. Seed germination was stimulated by heat (70° or 100° C) followed by a cold treatment. Burned plots contained 22-fold more seedlings than unburned plots, and seedling survival was significantly greater on burned plots. Exclosures significantly increased seedling survival on burned plots by 2 yr postfire. Plants on burned plots began to bloom and to branch layer (root at the nodes) by the sixth year postfire, with larger plants producing more fruits and being more likely to branch layer. I concluded that C. roderickii was similar to other species in the subgenus Cerastes in its obligate-seeding response to fire. However, its ability to branch layer enabled C. roderickii to increase plant density in burned plots, and thus continue postfire population recovery, long after fire-stimulated seedling establishment ceased. Branch layering by C. roderickii allows a postfire recovery pathway that is unique among species of obligate seeding Ceanothus studied to date.