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Satellite-Based Long-Term Monitoring of Saltcedar Control along the Riparian Corridor of the Lower Pecos River, Texas

Seiichi Nagihara1 and Charles R. Hart2
1 Texas Tech University, Lubbock, TX
2 Texas Cooperative Extension, Fort Stockton, TX

Vegetation along the lower Pecos River in Texas has been dominated by saltcedar for the past century. Many researchers believe that saltcedars, because of their invasive nature and dense populations, can withdraw more groundwater of the riparian corridor than native plants they have displaced and cause a reduction in stream flow. Along the Pecos and other rivers in west Texas, researchers are experimenting with various measures to control saltcedars. Here we describe a simple methodology based on satellite remote sensing for monitoring the impact of the saltcedar control measures in long terms. In 1999 through 2004, herbicides were sprayed from helicopters along some sections of the lower Pecos to exterminate saltcedars. Data from the Landsat 7 Enhanced Thematic Mapper Plus and the Advanced Spaceborne Thermal Emission and Reflection Radiometer from the same period were examined. First, normalized difference vegetation index (NDVI) images were derived from the satellite data. Then, using the change detection technique, we superimposed an NDVI image from one growing season over another. The superimposed image highlighted areas where vegetation was lost during the interval between the times when the two satellite data sets were acquired. The areas of vegetation loss indicated by the change detection image coincided well with the areas where herbicides were applied in the same time interval. This shows that the technique is useful in identifying areas where saltcedar treatment was effective. The same type of change detection technique was used also to locate areas of vegetation recovery after the herbicide application.