Soil and Community Characteristics Associated with Hazardia orcuttii (Asteraceae)

Abstract

Hazardia orcuttii (A. Gray) Greene is a 5–10 dm tall perennial shrub that is native to coastal sage scrub communities of southern California and northern Baja California. This species was listed as threatened by the California Department of Fish and Game in 2002 and is a federal candidate species, and the only known population in the U.S. is on a 1.6 ha mesa located in Encinitas, California. Very little is known about the general ecology of this species, thus, the goal of this research was to characterize the basic soil physical and chemical properties and plant community characteristics associated with this species. Research was conducted between January 2004 and July 2005 in 12.56 m2 randomly-located plots that either contained or lacked H. orcuttii. Soil in plots containing H. orcuttii had significantly higher clay, soil organic matter, total N, and soil moisture content than plots lacking H. orcuttii, while plots lacking H. orcuttii had significantly more surface litter content. Significant differences were also observed in plant species abundance between plots containing and lacking H. orcuttii, indicating fundamental differences in plant community composition associated with patches of H. orcuttii. Our data support the notion that H. orcuttii is a soil endemic; however, it is unclear whether H. orcuttii prefers soil richer in clay or is restricted to these soils because of other factors. Given the restricted nature of H. orcuttii, and the proximity of the extant population to residential areas, habitat protection from human degradation and fire should be a high priority.