Arundo donax Eradication in the LA River Watershed
Arundo donax, a highly invasive riparian plant species (commonly referred to as giant reed), has significant impacts on water availability, water quality (i.e. sediment loads, temperature, pathogens, nutrient loading, flow modification), habitat, fires, and infrastructure. Arundo transpires water at a rate that is 5x higher than native vegetation. Analysis from Cal-IPC’s Arundo donax Distribution and Impact Report (March 2011) demonstrates that for every one-acre of Arundo removed, 20 acre-feet per year (AFY) of water would be available downstream for capture/recharge into the San Fernando Groundwater Basin and for in-stream flows along the Glendale Narrows.
Arundo becomes so dominant in riparian systems that it changes hydrological and geomorphic processes that determine plant and wildlife community structure. These changes occur through alteration of flood disturbance and introduction of fire disturbance. Altered flood and fire regimes promote Arundo dominance and suppress native vegetation. In addition, Arundo stands can significantly increase fuel loads and fire frequency potential (acting as both an ignition source and fire conveyance across riparian areas).
Arundo also out-competes all native vegetation, impacting environmental resources and habitat beneficial uses. It has almost no biological value–no insects or wildlife feed on it, few organisms inhabit stands (i.e. poor nesting structure for birds), and stands impede movement in and through riparian zones. This directly impacts many terrestrial endangered and threatened species such as least Bell’s vireo, southwestern willow flycatcher, arroyo toad, and many others. Aquatic threatened and endangered species (e.g. Santa Ana sucker) are also affected by Arundo’s alteration of sedimentation processes, water temperature, eutrophication, and pathogens.
View the Arundo donax rating profile at Cal-IPC.
In partnership with parallel efforts occurring in the Tujunga Wash, Council for Watershed Health (CWH) is developing a program to eradicate approximately 80 acres of Arundo donax for the other remaining areas of the Upper Los Angeles River Watershed. Because Arundo spreads only by the dispersal of fragments downstream (no viable seed is produced), it is key to work from the top of a watershed towards the bottom. The Upper Los Angeles River subwatershed unit represents the headwaters of the larger Los Angeles River Watershed. This initiative will facilitate the development of programs that eradicate Arundo through use of the top-down treatment approach, generating long-term protection of water resources.
Jason Casanova, Program Manager (cas at watershedhealth dot org) or 213-229-9945