Giant reed (Arundo donax), also known as arundo, is an aggressive invader of riparian areas, ditches and other wet sites throughout California. It is not well established in Sequoia and Kings Canyon National Parks, but it is a species of special concern. Giant reed seems to have originated in Asia and has spread to southern Europe, the Middle East, Australia, and the Americas. It is considered to be well adapted to extreme fire events, and in fact it seems to promote fire. Arundo has the alarming tendency to displace nearly all native species from the areas which it invades. It is known to take over large portions of low-elevation stream beds and to form dense, very persistent thickets.
Photo by Brother Alfred Brousseau, St. Mary's College
Giant reed is a bamboo-like perennial grass that can grow up to eight meters (25 feet) in height. It has thick creeping rootstocks. The stems are hollow and can reach 4 centimeters (1.6 inches) in diameter. The flower clusters are plume-like, often purplish in color, and can reach 60 centimeters (2 feet) in height. Arundo turns mostly brown in the wintertime, and grows most vigorously in late spring and early summer. Aside from cultivated bamboo, there are no grasses in California that could be mistaken for giant reed.
Giant reed requires a tremendous amount of water to persist. This, coupled with its ability to quickly dominate entire stream channels, makes arundo a particularly pernicious weed in the thirsty state of California. Little is known about arundo's reproductive ability in California. There are no observations of the plant sexually reproducing in this state; it appears to spread to new locations via fragments of stems and rootstocks, especially during flood events.
There are a few small populations known to be in Sequoia National Park. All are in and around the Ash Mountain area. Natural Resource Management Personnel began eradication of this species in 2002.