Fire and dry grass: Effects of Pennisetum villosum on a California native, Nassella pulchra, in drought times

Invasive species pose a significant threat to many ecosystems, whether by outcompeting native species and disturbing food webs, or through increasing risks of natural disasters like flooding and wildfires. The ornamental grass species Pennisetum villosum R. Br. (also called Cenchrus longisetus M.C. Johnst.) was previously identified by the California Invasive Plant Council as being potentially invasive; this experiment was conducted to determine if P. villosum displays characteristics of an invasive species when grown in a California chaparral environment. This was done by growing it near a California native grass, Nassella pulchra (Hitchc.) Barkworth (also called Stipa pulchra Hitchc.), under both drought and non-drought conditions, and measuring the longest grass blades of each plant once a week. We found that in both conditions, the two species had similar germination rates, and that P. villosum grew significantly larger than N. pulchra for around 95 days. In control conditions, P. villosum then became reduced in size until it was significantly shorter than N. pulchra, while in drought conditions, there was no significant difference between the species. In this study, P. villosum did not negatively affect Nassella pulchra’s growth but may cause a fire hazard.