Century-old giant reed now fuels wildfires and drains water in Southern California
Giant reed, introduced to California in the 1820s for roofing and erosion control, has become an invasive weed that triples fire fuel and consumes vast water supplies in the state.
Arundo donax, known as giant reed, was first brought to California in the 1820s to provide roofing material and curb erosion, but its rapid growth—up to four inches a day—and tolerance for varied conditions have turned it into a pervasive invasive species. The plant now creates thick monocultures that displace native flora such as willows, reducing habitat for associated wildlife. In Southern California’s Santa Ana River Basin, these stands have almost tripled the fire fuel load in riparian areas and are well adapted to fire, allowing burns to reinforce their dominance.
Water consumption studies estimate the reed transpires about 56,200 acre-feet annually, a difference that could otherwise supply roughly 190,000 people. Flood events can also carry large reed fragments that threaten infrastructure like bridges. Scientists at the University of California and USDA-one outlet are testing herbicides, mechanical removal, and host-specific insects such as the Arundo wasp, scale, and fly as potential biological controls.
Why it matters
The invasive giant reed threatens ecosystems, water resources, and fire safety for millions of Californians.
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