Giant reed, also known as arundo, was brought to California in the 1820s and has since become an invasive weed that crowds out native plants and fuels wildfires. According to research, giant reed can grow up to 4 inches a day and reach 25 feet tall in just over a year, making it a highly effective spreader. The plant's impact is particularly severe in California, where it can choke out native willows and create a fire risk by providing large amounts of fuel in riparian areas. In the Santa Ana River Basin, giant reed infestations have almost tripled the fire fuel load, with an estimated 37,500 acre-feet of water being diverted from native vegetation each year.
Written by the local model on 2026-09-10,
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Story summary
Giant reed, a non-native plant that was introduced to California in the 1820s, has become an invasive weed in parts of the state, crowding out native plants and fueling wildfires. The plant, scientifically known as Arundo donax, was originally planted for its use as roofing material and erosion control, but it has since spread rapidly due to its ability to grow up to 4 inches per day and reach a mature height of 25 feet in just 12 months. According to the University of California, Riverside's Center for Invasive Species Research, giant reed has become a problem not only in California, but also in parts of Texas, Hawaii, Nevada, Utah, Missouri, Virginia, New Mexico, and Florida. The plant's invasive nature is attributed to its ability to thrive in various environmental conditions, making it a significant threat to native ecosystems.
Written for “Invasive Nonnative Plant Threats” on 2026-09-10,
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A plant brought to California nearly 200 years ago has become a serious invasive weed in parts of the state.
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plant → bring → state
Giant reed, also known as arundo, was first planted in California in the 1820s to provide roofing material and help control erosion in the Los Angeles Basin.
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reed → know → Basin
According to Center for invasive species research, the plant, scientifically known as Arundo donax, is native to eastern Asia.
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plant → accord → Asia
It was widely planted in different parts of the world because it could be used for several purposes, including walking sticks, fishing poles and musical instruments.
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it → plant → sticks
It is also being investigated as a possible biofuel source.
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Over time, however, giant reed became an
invasive weed in several regions where it was introduced.
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The University of California, Riverside’s Center for Invasive Species Research lists California among the areas where the plant has become a problem, along with parts of Texas, Hawaii, Nevada, Utah, Missouri, Virginia, New Mexico and Florida.
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plant → list → Texas
One reason giant reed can spread so effectively is its rapid growth.
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reed → spread → ?
The plant can grow about 4 inches a day and reach a mature height of 25 feet in about 12 months.
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plant → grow → months
It can also tolerate a range of environmental conditions, allowing it to grow in damp riparian areas and in moderately saline soils.
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it → tolerate → soils
Dense growth pushes out native plants
Giant reed can form dense stands that leave little room for native vegetation.
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that → push → vegetation
Native plants are typically displaced when arundo becomes established.
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arundo → displace → ?
Animals associated with those native plants may also be unable to use the dense stands of giant reed, leading to declines in their populations.
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Animals → associate → populations
The problem is particularly serious in California, where arundo can choke out native willows.
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arundo → choke → willows
Its presence also creates a fire risk because the plant can provide large amounts of fuel in riparian areas, where fires are typically uncommon.
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fires → create → areas
The plant is also well adapted to fire.
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plant → adapt → fire
This creates another problem because fires can help promote arundo invasions in sensitive habitats.
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fires → create → habitats
In the Santa Ana River Basin in Southern California, the fire fuel load in riparian areas has almost tripled because of arundo infestations.
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load → triple → infestations
The plant can create problems during floods as well.
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plant → create → floods
Large amounts of arundo can be dislodged and carried by floodwater.
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amounts → dislodge → floodwater
These pieces can form large rafts, and tons of the plant can build up around bridge supports.
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tons → form → supports
Such accumulations can cause bridges to collapse.
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bridges → cause → ?
Giant reed also uses large amounts of water
The invasive plant's impact is not limited to native vegetation and fire risk.
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impact → use → vegetation
Its water use has also been studied in the Santa Ana River.
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use → study → River
Research cited by the Center for Invasive Species Research estimated that arundo transpires 56,200 acre-feet of water each year on the Santa Ana River.
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arundo → cite → River
Native vegetation was estimated to consume 18,700 acre-feet.
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vegetation → estimate → feet
The difference was estimated at 37,500 acre-feet of water.
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difference → estimate → water
The study said that if arundo were not drawing this water from the Santa Ana River Basin, there would be enough water to serve a population of about 190,000 people.
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arundo → say → people
The same study estimated that purchasing that amount of untreated water from the Metropolitan Water Association would have cost approximately $12 million in 1993 dollars.
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purchasing → estimate → dollars
The economic study was conducted in 1993.
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study → conduct → 1993
Scientists studying ways to control it
Researchers at the University of California are studying the invasion ecology of arundo and different ways to control it.
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These include the use of herbicides and mechanical removal from areas where the plant has spread.
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plant → include → areas
Another approach being developed by USDA-ARS researchers in Texas is biological control.
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approach → develop → Texas
The strategy involves using natural enemies that feed on arundo and could reduce its growth.
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that → involve → growth
In California and other parts of the US, there are no organisms that cause substantial feeding damage or mortality to arundo.
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that → be → arundo
The lack of natural herbivores has partly allowed the plant to flourish in areas it has invaded.
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it → allow → areas
Researchers searching for arundo's natural enemies in its native range have identified several insects that could potentially reduce the plant's vigour by feeding on it.
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that → search → it
These include the Arundo wasp, Tetramesa romana; the Arundo scale, Rhizaspidiotus donacis; and the Arundo fly, Cryptonevra species.
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Safety evaluations have found that these insects are highly host-specific and pose no substantial threat to other plants.
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insects → find → plants
Efforts are now under way to mass rear these natural enemies and establish them in areas with severe arundo infestations.
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Efforts → rear → infestations
…and 4 more, not listed.
