Evaluation of color-infrared photography for distinguishing annual changes in riparian forest vegetation of the lower Rio Grande in Texas

Abstract

The Rio Grande is significant for its role in the history of the USA and Mexico and is the second longest river system in the United States. The riparian vegetation of the Rio Grande in Texas is poorly known. We employed aerial color-infrared (CIR) photography to investigate patterns of distribution, species composition, and annual changes in riparian vegetation at two sites in the lower Rio Grande Valley. The line-intercept technique of vegetation analysis was used to provide ground truth and to assist in the correlation of imagery and vegetation discrimination, distribution, and abundance. Celtis laevigata (sugar hackberry) was the dominant tree species at Bentsen-Rio Grande Valley State Park (BRG) near Mission, Texas, and Prosopis glandulosa (mesquite) and Parkinsonia aculeata (retama) were the dominant species at Salineño (SAL) near the outflow of the Rio Grande from Falcon Dam. Celtis pallida (granjeno) was the dominant shrub species at both sites, and the introduced grasses, Panicum maximum (Guineagrass) and Cenchrus ciliaris (buffelgrass) were the dominants in the ground layer at BRG and SAL, respectively. Aerial CIR photography appears to be useful in discriminating certain tree species. However, due to tonal similarities, it is difficult to identify each of the species in the canopy. An important value of the technique is the monitoring of senescence and death of trees in the riparian zone between successive years.