Passive restoration potential of riparian areas invaded by giant reed (Arundo donax) in Texas

Authors: Racelis, Alexis; RUBIO, AMEDE - Texas A&M University; VAUGHAN, THOMAS - Texas A&M University; Goolsby, John

Submitted to: Ecological Restoration
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2012
Publication Date: 2/28/2012
Citation: Racelis, A.E., Rubio, A., Vaughan, T., Goolsby, J. 2012. Passive restoration potential of riparian areas invaded by giant reed (Arundo donax) in Texas. Ecological Restoration. 30(2):103-105.

Interpretive Summary: Much of the riparian areas of the Rio Grande Basin has been invaded by the exotic woody grass, giant reed (Arundo donax L.). The negative impacts of this weed include the displacement of rare riparian habitats and the associated ecological services, such as biodiversity and water enhancement. Giant reed is also considered a threat to both border security and agricultural security and as such, much effort has been given to control this weed, even in the absence of knowledge of the potential for restoration of giant reed infested areas after control. We conducted a 27 month study of the passive restoration potential of giant-reed infested areas by periodically removing all giant reed from 16 - 25m2 permanent observation plots in Laredo Texas. Initially, all plots were dominated by giant reed. Species abundance increased significantly over the observation period, during which we recorded a total of 44 non-giant reed species, of which two-thirds are native riparian trees. We found a wide diversity of plant life forms at the end of the study, including many herbaceous plant species (25 spp.), vines (2 spp.), and five species of native trees characteristic of riparian areas of south Texas. Our results suggest the implementation of natural enemies or a well timed combination of mowing and selective removal and can be a good way to sustain control of giant reed so as to allow the passive restoration of a great diversity of riparian vegetation.

Technical Abstract: Giant reed (Arundo donax L.) is a rhizomatous woody non-native grass that has invaded much of the riparian areas of the southwest. By forming thick impenetrable swaths along riverbanks and waterways, giant reed has driven riparian ecosystem decline and displaced native biodiversity. It’s documented negative impacts to both water supply and border security along the Rio Grande further justifies an intensive effort to control this weed. Current methods include chemical herbicides, mechanical removal, and biological control with the use of natural enemies. Not much is known about the successional response of these areas or the potential for riparian restoration after the effective control of giant reed. To determine restoration potential of these areas, we documented emergent plant species after periodic treatments of above ground removal of giant reed in infested areas near Laredo, Texas. At each visit we removed all existing above ground giant reed stems within each plot. We counted all other plant species that were present in the plot at the time of sampling and identified them using botanical field guides. Initially, our observation plots were completely dominated by giant reed. Overall species abundance increased significantly over the observation period, during which we recorded a total of 44 non-giant reed species. A linear regression was used to test the increase of species abundance of both native and non-native species after periodic removal of giant reed. In each case, the model proved significant, although the rate of increase in the abundance of native species (ß=1.06, t(11)= 6.34, p<0.001) was greater than the rate of increase of non-native species (ß=0.28, t(11)= 4.53, p=0.001). We also found a wide diversity of plant life forms at the end of the study, including many herbaceous plant species (25 spp.), vines (2 spp.), and five species of native tree saplings characteristic of riparian ecosystems of south Texas. Our results indicate a strong potential for passive restoration of giant reed infested areas, but only after repeated removal of giant reed shoots for one year or more. This research can help inform land managers that have the restoration of giant-reed infested riparian areas as a goal.