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Title: Mapping giant reed (Arundo donax) infestations along the Texas-Mexico portion of the Rio Grande using aerial photography

Author
item Yang, Chenghai
item EVERITT, JAMES - Retired ARS Employee
item Goolsby, John

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2011
Publication Date: 12/31/2011
Citation: Yang, C., Everitt, J.H., Goolsby, J. 2011. Mapping giant reed (Arundo donax) infestations along the Texas-Mexico portion of the Rio Grande using aerial photography. Journal of Invasive Plant Science and Management. 4:402-410.

Interpretive Summary: Giant reed is an invasive weed throughout the southern half of the United States with the densest stands growing along the coastal rivers of southern California and the Rio Grande in Texas. This study used aerial photography to map giant reed infestations and estimate infested areas along the Texas-Mexico portion of the Rio Grande. The total giant reed area along the Rio Grande between Lajitas and San Ygnacio was estimated to be 5985 ha with 3670 ha or 61% on the U.S. side and 2315 or 39% on the Mexican side. Furthermore, the U.S. and Mexico each had about 50% of the giant reed along the portion of the river between Lajitas and Del Rio, while the U.S. had 2/3 of the giant reed on the portion of the river between Del Rio and San Ygnacio. The results from this study will be very useful for both land owners and government agencies for the management and control of this invasive weed along the Rio Grande in both the U.S. and Mexico.

Technical Abstract: Giant reed is an invasive weed throughout the southern half of the United States with the densest stands growing along the coastal rivers of southern California and the Rio Grande in Texas. The objective of this study was to use aerial photography to map giant reed infestations and estimate infested areas along the Texas-Mexico portion of the Rio Grande. Aerial color-infrared photographs were taken along the Rio Grande between Brownsville and El Paso, Texas in June and July 2002. Based on the aerial photographs and ground surveys, the portion of the river from San Ygnacio to Lajitas that has a river length of 898 km (558 mi) was found to be infested with giant reed. To estimate infested areas along both sides of the river, 65 out of the 480 aerial photographs taken between Lajitas and San Ygnacio were randomly selected. The aerial photographs were digitized, rectified to Google Earth imagery, and then classified using maximum likelihood classification techniques. The infested areas on both sides of the river as well as water area and river length from each photographic image were determined. Based on the estimates from the 65 aerial photos, the ratio of giant reed area to water area and the ratio of giant reed area to river length were calculated. The total giant reed area along the Rio Grande between Lajitas and San Ygnacio was estimated to be 5,985 ha (14,790 ac) with 3,670 ha or 61% on the U.S. side and 2,315 ha or 39% on the Mexican side. This study provides the first accurate estimates of giant reed infestations along the Texas-Mexico portion of the Rio Grande and will be useful for both land owners and government agencies for the estimation of water usage and economic loss and for the management and control of giant reed.