Although most people are not aware of this, Arundo donax is actually an extremely invasive and problematic weed
areas of the western United States
(as well as other areas). Arundo donax is probably originally native to eastern Asia
, although it has been transmitted all over the world by humans. It probably found its way to California
in the 1800s. Sometimes it was accidentally transmitted, due to the fact that every node
of the plant can form a whole new plant quickly. Other times, it was planted as a screen, for the uses noted in Vivid
's writeup, or even to stabilize bank
s (for this task it is actually unsuited because of its many problems and because of its shallow root structure).
People did not notice the problems with Arundo until it had become firmly established along waterways of the West. By then it was well-established, as it still is today. Major areas of infestation are the seasonally-flooded rivers in Southern California such as the Santa Clarita River, creeks along the Central Coast, and the Sacramento River Delta. The problems with Arundo are numerous; for the sake of brevity, only the worst will be noted here:
Clogging of stream channels
Since Arundo is so invasive, it can quickly fill the channels of streams, washes, and irrigation ditches. This constricts the flow of the water, and vastly modifies the nature of the river. In irrigation channels, the weed can slow the flow of water to a trickle in a few years, requiring costly removal. In natural waterways, Arundo is a huge problem during floods. The extremely dense thickets of Arundo keep floodwaters from draining quickly, often causing WATER to back up and flood nearby areas. If the flood is large enough to remove the Arundo, often it becomes lodged under bridges, in culverts, or in other constricted areas, causing structural damage, sometimes even leading to the destruction of these structures by floodwaters. It can even root in these areas, causing new thickets in the future.
Even when green, Arundo is extremely flammable. Usually, creekside areas act as buffers for fires, halting a fire, or at least slowing it down. When Arundo is present, the fires can quickly spread into the canopy of other trees or to nearby houses, from the inferno of 15 foot tall dry burning grass. This can completely ruin a riparian ecosystem, destroy nearby structures, and add to flooding the next year. And Arundo's roots usually survive these fires, ensuring that without removal the cycle will repeat.
Removal of water
Since these plants grow so quickly and use so much water, their presence can dramatically decrease the amount of water in streams, rivers, and channels, increasing the severity of droughts
Crowding out native organisms
Arundo is so thick and inpenetrable that almost no animals can live in it. Its leaves are unpalatable to most livestock. Their roots and stems destroy fish habitat. And the plants themselves crowd out important riparian plants such as alder, oak and cottonwood. Since the arundo roots aren't as deeply planted as those of the native plants, erosion of an arundo-infested river may actually increase.
So what do we do about it???
Arundo has proved to be extremely difficult to eradicate. However, there is hope. Arundo can be mechanically removed, via removing the stems at the base, or pulling smaller plants from the ground. The clippings must be removed or burned, or they will re-root. In the case of larger plants, this will have to be done many times as the plant will re-sprout from the rhizomes. Unfortunately, the plant usually must also be sprayed with herbicide to kill the rhizomes. This is usually done in the late summer or early fall when the plant is transporting its energy to the roots. Spraying immediately after cutting the stems is especially effective. Burning Arundo usually is not an effective method of control, as Arundo quickly resprouts after burns, and the dried stems present a large fire danger.
Perhaps the most important step in reducing this infestation is stopping its spread. This plant does not reproduce from seed in California; only from displaced rhizomes or stems. Many nurserys still sell Arundo as a landscape plant. This must be stopped, or at least people must be aware of the consequences of planting this weed.
More information on Arundo may be found at these sources: