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Environmental and Community Factors Influencing the Distribution of Pennisetum setaceum in California

  • Author(s): Sweet, Lynn
  • Advisor(s): Holt, Jodie S
  • et al.
Abstract

Non-native African fountain grass (Pennisetum setaceum) has been increasing in California over the last century; however, its potential distribution and impacts have not been determined. Coarse-scale species distribution models trained using data from the native range of P. setaceum indicated broad areas of suitability for P. setaceum in southern and coastal California. MaxEnt models produced using native range information showed a broader potentially suitable area than models based on the invaded range data. At a finer scale, suitable area in the Colorado Desert occurs where there are factors associated with increased soil moisture. This study demonstrates that these methods can be used to provide regional risk-planning information as well as to inform local early-detection efforts. Within this broader area, biotic factors also influence invasion. Where P. setaceum occurs adjacent to native C3 Stipa pulchra grasslands, it is unknown whether differences in physiology between the two species will be conducive to or prevent invasion by P. setaceum into S. pulchra-dominated areas. A competition experiment was carried out to determine the competitive interactions of the two species from the cool winter season into the warm summer season. Results of this study showed that P. setaceum may experience intense competition by S. pulchra in the cool season but a release from this competition and an opportunity to thrive later in the season. As little is known about potential impacts of P. setaceum on coastal sage scrub communities in southern California, several sites were analyzed during two growing seasons for cover of native and exotic species and soil nutrients in areas containing P. setaceum. With increased cover of P. setaceum, reductions in native species cover were found in both years in Santa Monica Mountains (SAMO) sites and in one year in San Diego sites; reductions in native species richness were found in both years in SAMO; and higher nitrate, soil water content and potassium were found in both regions in the second year. Rarefaction analysis of beta-diversity showed smaller differences between invasion levels than expected. These potential impacts of P. setaceum call into question the use of this ornamental grass in landscaping.

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