Invasiveness and reduction of biodiversity
The propagation of Arundo donax is generally not of concern in its native range, but may become an important issue in areas where it has been naturalized, such as the subtropical USA (CABI, 2014; Ryan, 2001). It outcompetes a wide range of native species and quickly becomes the dominant species in riparian areas where it forms dense monospecific thickets (Scott, 1994). For instance, the giant reed was reported to dominate 68% of the vegetation of the Santa Ana River Basin in California (Douthit, 1994). This ability to outcompete other species is reinforced by its response to fire: Arundo donax produces year-round large amounts of flammable material that increase the intensity of fires, but, because of its rhizomes, it quickly re-sprouts after fires, preventing the re-establishment of other species (Scott, 1994). The disappearance of native plant species due to Arundo donax alters biodiversity. Not only bird species that depend on native plant species for feeding or nesting lose their natural habitat, but the giant reed also provides little shade unable to cool in-stream habitats for fish and invertebrates (Ryan, 2001). The giant reed also provides a habitat for the invasive Norway rat (Rattus norvegicus), which has caused or contributed to the extinction or reduction of native range animal species (CABI, 2014). Cattle, sheep and goats may be useful to control the giant reed population. For instance, Angora goats have been partially successful in reducing this plant in Southern California (Daar, 1983). However, grazing is unlikely to reduce population size significantly (USDA, 2012).
Water depletion
The giant reed uses more water than native plants, lowering groundwater tables (CABI, 2014).
Alteration and obstruction of waterways
The extensive root system of Arundo donax inhibits the movement of water and sediments. In periods of flooding, reed thickets force flood waters out of the primary channels. The stems and rhizomes break off and are deposited in drainage systems, under bridges, in agricultural ditches and other flood control systems, thus obstructing them (CABI, 2014).
Erosion control and wind breaks
Arundo donax was planted in California in the late 1700s and early 1800s for erosion control in drainage canals and as windbreaks (Csurhes, 2009). It is still used in gardens for erosion control (Ryan, 2001).
Second generation energy crop
In the USA, in spite of its invasiveness, the Environment Protection Agency agreed that the giant reed can be used as a source of biofuel under the Renewable Fuel Standard Program provided users respect the Risk Management Plan for early detection and rapid response to potential spread (EPA, 2013).
Wastewater treatment
The giant reed can be valuable for wastewater treatment. In Portugal, it was effective in the treatment of tannery wastewater (Calheiros et al., 2012). In Sicily, giant reeds planted in constructed wetland systems significantly removed pollutants from urban wastewater, and the treated water was used to irrigate parkland areas (Leto et al., 2013).