Arundo donax Removal
in the Los Angeles and San Gabriel River Watersheds
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Background
Arundo donax, an introduced riparian plant species (commonly referred to as giant reed), has significant negative 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.
Contact
Drew Ready, Program Manager (drew at watershedhealth dot org) or 213-229-9945
Partners
Programs
In partnership with parallel efforts occurring in the Tujunga Wash sub-watershed (with a baseline of 100+ acres of Arundo), Council for Watershed Health (CWH) is managing a program to remove approximately 80 acres of Arundo for the other remaining areas of the Upper Los Angeles River Watershed. This program is in its third year of implementation. 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 remove Arundo through use of the top-down treatment approach, generating long-term protection of water resources.
In addition, CWH is currently developing an implementation plan and finalizing permits that will launch a new program in the Rio Hondo and San Gabriel River Watersheds. Initial implementation is scheduled to begin in Fall 2025. Status maps and planning resources for both programs are available below.
Resources
Upper LA River Watershed Removal Status Map (current) - updated treatments and current Hansen Dam footprint (excluding historic baseline data - see map below for initial acreages)
Upper LA River Watershed Removal Status Map (archived) - contains historic Hansen Dam Recreation Area baseline data
Upper LA River Watershed Programming Areas Map (archived) - Implementation Plan map broken down by sub-watersheds
Upper LA River Watershed Implementation Plan (pdf)
Rio Hondo and San Gabriel River Watersheds Removal Status Map - DRAFT (in development)
