|Institution:||University of California – Santa Cruz|
|Keywords:||Ecology; Invasive species impacts; Management; Restoration|
|Full text PDF:||http://www.escholarship.org/uc/item/1bq9k8hn|
Ehrharta erecta (panic veldt grass) is an actively spreading invasive grass in California with an uncommon capacity to invade forest understory. Greater understanding of the ecology, impacts, and potential for control of this invader is needed to set priorities and guide management. In a mixed-evergreen forest in Santa Cruz County, we measured impacts of E. erecta on native plant species richness and abundance, quantified the effectiveness of mechanical and chemical management methods, and tested whether this species forms a seed bank. We found lower percent cover of native species in plots invaded by E. erecta compared to nearby non-invaded plots, but we did not find significant differences in species richness, and we did not find a significant relationship between E. erecta cover and native cover in invaded plots. Strikingly, we measured nearly four times greater total vegetation cover in E. erecta invaded plots. Twenty-two months following management treatments, we found significant reductions in E. erecta using both mechanical and chemical methods. Herbicide application produced greater non-target effects. In a separate experiment, we tested the effects of native plant addition on restoration outcomes and regrowth of E. erecta. Transplanting native Clinopodium douglasii into management plots did not slow regrowth of E. erecta. Transplants did increase the percent cover native plants, but only by increasing C. douglasii itself. Finally, in a greenhouse experiment we compared the number of E. erecta germinants from duff and soil collected from two depths. Ehrharta erecta germinated from all three substrates, with the greatest number of germinants in the upper soil layer, suggesting that E. erecta seeds accumulate in the soil over time. The results of this research demonstrate that E. erecta drives ecological change in a mixed-evergreen forest community, effective management is possible using manual and chemical removal methods, and restoration of native species can be promoted through planting. Since we found evidence that E. erecta forms a seed bank, we recommend rapid response to E. erecta invasion and consideration of management methods that have low soil disturbance in treating established E. erecta populations.