Endangered Species Recovery Program
California Department of Fish and Game
Sacramento, CA 50 pp.
Ellen A. Cypher
Populations of two endangered and one threatened plant species were studied on the Carrizo Plain Natural Area (CPNA) and in the San Joaquin Valley of California in order to provide baseline data for continuing research on their ecology and responses to drought and site management. Results will be incorporated into a multi-species recovery plan as well as restoration and management plans for the CPNA and other preserves.
In terms of plant size and reproduction, the most successful populations of Caulanthus californicus were those on the CPNA, whereas Lembertia congdonii was equally successful on the CPNA and in the Kettleman Hills. Of the four Eriastrum hooveri sites studied, plants on the CPNA were smallest with poorest reproduction.
Grazing effects were compared in three populations of L. congdonii, each of which was divided into grazed and ungrazed portions. Reproduction of L. congdonii was greater in grazed than in ungrazed areas of the Carrizo Plain and Kettleman Hills, whereas the reverse was found on the Elkhorn Plain.
Distribution and morphological characters of C. californicus and L. congdonii were evaluated relative to giant kangaroo rat (Dipodomys ingens) precincts on the Carrizo and Elkhorn Plains. Although C. californicus occurred more frequently on precincts than did random points, plants growing on precincts did not differ significantly in size or reproduction from those growing between precincts. Conversely, L. congdonii occurred randomly with respect to precincts. The two L. congdonii populations studied differed in plant response to giant kangaroo rat precincts in terms of plant size and flower head production, but not in survival and achene production.
Habitat characteristics of the listed plant and animal species were assessed on 19 vegetation transects on the CPNA and 43 in the San Joaquin Valley. Exotic plants dominated in cover at most sites, yet exotics accounted for less than one-third of species composition, on average. Plant diversity was high on the CPNA compared to other areas sampled, and species richness was greater in ungrazed than in grazed areas. Native plants, including the listed species, apparently persisted in the seed bank during the recent drought.
Reintroduction of Caulanthus californicus, Lembertia congdonii, and Eriastrum hooveri is not necessary on the CPNA at this time. Exotic plants are not likely to be eradicated from the area, but active management (e.g., planting, seeding, burning) could increase the proportion and distribution of native plants, particularly shrubs and perennial grasses. Controlled grazing studies are a prerequisite to management decisions. Additional research is necessary to determine the extent of the existing seed bank and the appropriate management techniques for enhancement of rare plant populations and rehabilitation of plant communities affected by drought and historic agricultural practices.