Demographic monitoring of endemic sand dune plants, Eureka Valley, California

Abstract

A two-year study of the perennial endemics Swallenia alexandrae, Oenothera avita ssp. eurekensis and Astragalus lentiginosus var. micans was conducted at Eureka Dunes, Inyo County, California. Based on analyses of survivorship it was concluded that the populations are at least stable (even short-lived Oenothera cohorts survive long enough to reproduce) or growing (the number of established Swallenia and Astragalus plants doubled during the study). The high mortality and short life span of Oenothera and Astragalus populations were offset by copious seed production, long-lived seeds, low to moderate seed predation, and frequent establishment. The low and variable seed production, high seed predation, and infrequent establishment of Swallenia populations were counterbalanced by a low mortality of recruits and established plants, a long reproductive life, and long-lived seeds. It is concluded that the factors endangering these endemic populations are mostly extrinsic to the plant population (e.g. human disturbance, pollinator availability, climatic fluctuation) and that no additional manipulations of the populations are necessary.