Livestock grazing represents a major human alteration of natural disturbance regimes in grasslands throughout the world, and its impacts on plant communities have been highly debated. We investigated the impact of cattle grazing on the California coastal prairie plant community with a focus on native annual forbs, a number of which are of conservation concern. In spring 2000 and 2001, we surveyed the vegetation community composition, vegetation structure, and soil chemical parameters at 25 paired grazed and ungrazed sites over a 670-km range of the ecosystem. Native annual forb species richness and cover were higher in grazed sites, and this effect was concomitant with decreased vegetation height and litter depth. Soil properties explained less of the variation. Exotic annual grass and forb cover were higher in grazed sites. Native grass cover and species richness did not differ in grazed and ungrazed sites, but cover and species richness of native perennial forbs were higher in ungrazed sites. Our results suggest that cattle grazing may be a valuable management tool with which to conserve native annual forbs in the ecosystem we studied but that grazing differentially affects the various life-history guilds. Therefore, land managers must focus on creating a matrix of disturbance regimes to maintain the suite of species native to these mesic grasslands. The results of this and other studies highlight the importance of considering the adaptation of vegetation communities to disturbance in making recommendations for grazing management. Impactos del Pastoreo de Ganado sobre Hierbas Anuales y la Composición Vegetal de Pastizales Mésicos en CaliforniaResumen: El pastoreo de ganado representa una importante alteración humana de los regímenes de perturbación natural en los pastizales del mundo, y sus impactos sobre las comunidades vegetales han sido ampliamente debatidos. Investigamos el impacto del pastoreo de ganado sobre la comunidad de plantas en la pradera costera de California conénfasis en hierbas nativas anuales, de las cuales varias son de preocupación para la conservación. En la primavera de 2000 y 2001, estudiamos la composición de la comunidad vegetal, estructura de la vegetación y parámetros químicos del suelo en 25 pares de sitios con pastoreo y sin pastoreo en una extensión de 670 km del ecosistema. La riqueza y cobertura de hierbas nativas anuales fueron mayores en sitios pastoreados, y este efecto fue concomitante con una disminución en la altura de la vegetación y la profundidad de la hojarasca. La variación fue menos explicada por las propiedades del suelo. La cobertura de pasto y hierbas exóticas fue mayor en sitios con pastoreo. La cobertura y riqueza de especies de pasto nativo no difirió en sitios con y sin pastoreo pero la cobertura y riqueza de especies de hierbas perennes nativas fue mayor en sitios no perturbados. Nuestros resultados sugieren que el pastoreo de ganado puede ser una valiosa herramienta de gestión para conservar hierbas nativas anuales en el ecosistema que estudiamos pero que el ...

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Grasslands are hot spots of biodiversity but are now widely threatened by changes in patterns of disturbances, such as grazing and fire regimes, exotic species invasions, and cultivation. The goal of this experiment was to find the most appropriate combination of treatments to reintroduce Danthonia californica, a formerly dominant perennial bunchgrass, into degraded California coastal prairies. Danthonia californica was sown from seed and transplanted at two sites and at two grazing intensities (grazed/ungrazed) in a multifactorial experiment testing the effects of (1) local versus nonlocal seed sources; (2) topsoil removal; and (3) reduction of plant neighbors. Seed emergence was very low, suggesting that transplanting may be a better option to reintroduce D. californica. Although transplants grown from nonlocal seeds survived better initially at both sites, transplants from local seeds had higher survival after 1.5 year at one site. This suggests that short-term plant establishment studies may be misleading. Topsoil removal greatly enhanced transplant survival, and neighbor removal primarily increased transplant growth. Our results suggest that removing topsoil prior to transplanting seedlings grown from local seeds is the most promising method to reintroduce D. californica. However, the benefits of removing topsoil to provide safe sites for plant establishment should be weighed carefully against potential negative effects on the native seed bank and microbial communities on a sitespecific basis.

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Introducing rare plants to new sites for conservation to offset effects of habitat destruction requires detailed knowledge of habitat requirements, plant demography, and management needs. We conducted a factorial experiment replicated at three coastal prairie sites to test the effects of clipping frequency and litter accumulation on seed germination, seedling survival, reproduction, and seedling recruitment of introduced populations of the endangered, tall-stature, annual forb, Holocarpha macradenia (DC.) E. Greene. Clipping favored H. macradenia, primarily by enhancing seed germination and flower production. Litter accumulation had no effect on seed germination, even after 5 years of treatments. Seedling recruitment was highly site specific with large numbers of recruits recorded at only one of three sites. Although recruitment of seedlings was higher in clipped plots for 2-3 years, by 4-5 years after introduction very few seedlings survived to reproduction in any treatment. We attribute this result to a combination of poor habitat quality, small population size, and lack of a seed bank. We were unsuccessful in introducing this relatively well-studied species of concern to apparently suitable habitat at multiple sites in multiple years, which suggests that translocating rare plant populations to mitigate for habitat destruction is an expensive and highly uncertain endeavor.