Demographic Performance of a Rare California Endemic, Chorizanthe pungens var. hartwegiana (Polygonaceae)

Managing and understanding the ecology of endemic plants depends upon understanding the habitat limitations of these highly restricted species. Using transplant experiments we quantified the demographic performance of an endangered annual plant of coastal California, Chorizanthe pungens var. hartwegiana (the Ben Lomond spineflower), in habitats with established populations and in nearby habitats where the plant is never or rarely found. Habitats used for transplants occur on the sandhills soil outcrops to which this species is endemic, including open pine forest, manzanita-dominated chaparral and open erosive sand habitat. We monitored effects of transplant habitat, site from which the transplants originated and intraspecific density on the mortality, final biomass and reproductive effort of individual spineflowers. Habitat largely influenced biomass and reproductive effort and had little effect on mortality. Although spineflowers are currently absent from both pine and chaparral habitats, transplants grew and reproduced best under pines, and worst under chaparral, with intermediate performance in the open areas to which spineflowers are currently restricted. While the habitat needs of spineflowers impose severe restrictions on their population size, management could enhance establishment in pine-dominated areas adjacent to current populations. Patterns of spineflower performance suggest that endemic plants may be excluded from potential habitats by a multiplicity of factors, complicating management for the viability of such species.