The Santa Ana Watershed Project Authority (SAWPA), in collaboration with Riverside County Regional Park and Open-Space District and the Santa Ana Watershed Association, has been working on a way to wipe out the invasive plant Arundo donax, a species which the California Invasive Plant Council classifies as one of the top most invasive wildland pest plants.

An Invasive Problem

Arundo donax, commonly known as giant reed, is a hardy water loving plant that can survive flood, fires, and high salinity levels. It is considered a fire hazard and a burden to local and state fire departments. According to a 2011 California Invasive Plant Council Report, the plant has been a problem for water related agencies because it has been known to cause flooding by altering flow regimes and uses 600% more water in comparison to native vegetation.

It can also negatively impact water quality through increased water temperature due to limiting natural vegetation canopy along waterways, which can lead to algal growth and unhealthy pH levels affecting wildlife.

Strategies for Removal of the Plant

The removal of Arundo donax is often implemented through an initial stage of mechanical removal followed by a period of maintenance, usually done through application of herbicide.

The Riverside County Regional Park and Open-Space District operates a local mitigation bank whereby the funds from the sale of the bank’s credits fund the removal and treatment of Arundo donax and other heavy water using invasive plants in the Santa Ana River Watershed. The bank allows for project proponents or developers who have mitigation needs to purchase credits in lieu of implementing mitigation themselves.

Active Restoration in the Santa Ana River Watershed

DSCN1645 Much work is put into the initial removal of Arundo donax in the Santa Ana River Watershed; however, there is a need to maintain removal sites due to the germination of the plant through its rhizomes. According to an excerpt published by the Contra Costa Resource Conservation District, Arundo donax rhizomes can dry out for six months, yet still start growing vigorously whenever they come in contact with moisture.

Post removal, active methods such as native revegetation, are used to buffer against Arundo donax reinvestation. Research by Dr. Kai Palenscar, currently with the U.S. Fish and Wildlife Service, has shown that native mulefat provides a great resistance to Arundo donax regrowth and that even minor passive restoration sites found close to waterways were likely to recruit native species.

Through SAWPA, approximately 6,000 acres of Arundo donax in the Santa Ana River Watershed were removed and maintained. By extracting figures from the Invasive Plant Council’s research, this removal is estimated to provide approximately 70,000 acre feet per year of water to the region; enough water to support 140,000 families per year.

Purchasing Mitigation Bank Credits SAR-Mitigation-Bank-Logo_new-website

The Santa Ana River Mitigation Bank is implemented under an agreement with the U.S. Army Corps of Engineers. If you are interested in purchasing credits, please submit an email to SAWPA at iachimore at sawpa dot org and the Riverside County Parks Finance Office at Parks-Finance at rivcoparks dot org.

A memo will be prepared for you upon receipt of the email. The minimum purchase is ¼ of an acre. Acreage credit is available on a first-come-first-served basis.

For more information, please visit