Grazing maintains native plant diversity and promotes community stability in an annual grassland

Abstract

Maintaining native biodiversity in grasslands requires management and mitigation of anthropogenic changes that have altered resource availability, grazing regimes, and community composition. In California (USA), high levels of atmospheric nitrogen (N) deposition have facilitated the invasion of exotic grasses, posing a threat to the diverse plant and insect communities endemic to serpentine grasslands. Cattle grazing has been employed to mitigate the consequences of exotic grass invasion, but the ecological effects of grazing in this system are not fully understood. To characterize the effects of realistic N deposition on serpentine plant communities and to evaluate the efficacy of grazing as a management tool, we performed a factorial experiment adding N and excluding large herbivores in California's largest serpentine grassland. Although we observed significant interannual variation in community composition related to climate in our six-year study, exotic cover was consistently and negatively correlated with native plant richness. Sustained low-level N addition did not influence plant community composition, but grazing reduced grass abundance while maintaining greater native forb cover, native plant diversity, and species richness in comparison to plots excluding large herbivores. Furthermore, grazing increased the temporal stability of plant communities by decreasing year-to-year variation in native forb cover, native plant diversity, and native species richness. Taken together, our findings demonstrate that moderate-intensity cattle grazing can be used to restrict the invasive potential of exotic grasses and maintain native plant communities in serpentine grasslands. We hypothesize that the reduced temporal variability in serpentine plant communities managed by grazing may directly benefit populations of the threatened Edith's Bay checkerspot butterfly (Euphydryas editha bayensis).

Trade‐off between early emergence and herbivore susceptibility mediates exotic success in an experimental California plant community

“…Smaller, later‐emerging native species however would be relatively less apparent and accessible when growing with larger heterospecific competitors in polyculture than with similar sized conspecifics in monoculture; therefore, growth in polyculture may provide associational resistance (Underwood et al., 2014). Furthermore, native species can benefit from competitive release if early‐active exotic species are preferentially consumed (Beck, Hernández, Pasari, & Zavaleta, 2015). …”

Drought exacerbates negative consequences of high‐intensity cattle grazing in a semiarid grassland

“…) or even positive effects on plant diversity and ecosystem stability (Beck et al. , Alberti et al. ).…”

Impact of the Occurrence of Taraxacum Officinale F.H.WIGG. On Floristic Diversity and Utilisation Values of Meadow-Pasture Communities

“…7, which confirms that an increasing share of dandelion in the sward is positively correlated with values of R and N. In turn, an increase in the share of Taraxacum officinale is accompanied by a greater share of segetal and ruderal species, which is connected with a greater insolation of the area. These factors contribute to the poorer floristic structure of phytocoenoses, as manifested by a lower number of recorded species (Kiss et al 2011;Beck et al 2014). It needs to be stressed that the absence of dandelion in the sward is frequently connected with a greater share of species representing the class of Phragmitetea, and thus greater natural values.…”