Date of Graduation
Master of Science in Environmental Management (MSEM)
College of Arts and Sciences
The highly invasive grass species, giant reed (Arundo donax), has been a major contributor to riparian habitat degradation in California for over 50 years. Several modes of vegetative reproduction have allowed this alien species to take advantage of fluvial processes and rapidly spread within California watersheds. A. donax dramatically alters hydrologic regimes, displaces native vegetation, and removes food and habitat for native wildlife. It is widely accepted that removal of this invasive on a watershed scale is critical to restore natural riparian processes and facilitate the reestablishment of native flora and fauna. The following study analyzed the efficacy of past eradication projects and the subsequent recovery of native vegetation through either passive or active means. Through this analysis, recommendations were made for prioritizing removal sites, determining the most effective removal methods, and employing passive or active revegetation. This study determined the the three highest priority removal sites applicable to a wide variety of California watersheds are: upper watershed, largest A. donax infestations, and infestations in close proximity to fire prone areas. The most cost-effective removal method for large A. donax clumps is foliar spray with a 3-6% glyphosate solution. To minimize the use of herbicide and remain within the legal limit of 7qt/acre, mechanical removal should be used for large infestations whenever access allows for the use of heavy machinery, especially near urban areas. For moderate to small clumps, the most effective control methods are “bend and spray/hook” (3-6% glyphosate) and “cut-stem,” (100% glyphosate). Cut-stem is recommended near urban areas to avoid overspray or when A. donax is mixed in with native vegetation. If active revegetation is required, all A. donax should be removed prior to revegetation to eliminate the threat of reinvasion; the only exceptions to this are when it is necessary to immediately restore habitat for sensitive species or when erosion is a major concern. Due to the high costs of active revegetation and the lower ecological value of artificially plant riparian forests, passive revegetation should be used whenever possible. A. donax eradication on a watershed scale is feasible with proper planning, but the process may take 20 years or more depending on the size of the infestation.
Waterworth, Matthew S., "Prioritizing the Management of Arundo Donax: Recommendations for Removal and Revegetation in California Riparian Habitats" (2015). Master's Projects. 274.