| Wetlands, known as cienegas, were once found throughout the basin and range physiographic province in southeastern Arizona, southwestern New Mexico, northern Sonora, and northwestern Chihuahua. These groundwater-dependent wetlands are now largely desiccated due to overgrazing, groundwater depletion, and the resulting incision of streams and rivers. This study consists of four components. First, a more complete inventory of the location of historical cienegas is compiled. This is accomplished using peer-reviewed journal articles, historical maps, journals from explorers and pioneers, and USGS topographic maps. Second, the geographic extent of the documented cienegas is hand-digitized through photo interpretation of aerial imagery. Each cienega is divided by its activity status and the land cover succession path it followed. Third, the zonal statistics for a suite of Landsat Thematic Mapper (TM)-derived indices and elevation derivatives such as slope and aspect are compiled. Geospatial datasets that exhibit low variability among different succession paths are further analyzed as being possible predictor variables for the status or land cover type succession path of a cienega. The two best predictor variables are the normalized burn ratio (NBR) and the thermal infrared (TIR) band. These two variables are used in a classification tree model to determine the location of other undocumented areas that are likely active cienegas. The fourth component involves monitoring the trends of inactive, as well as active, cienegas over the past 25 years using the two most sensitive predictor variables. The interannual variability is indicative of changes in vegetation cover, as well as the degree of saturation of the soil. This component indicates that inactive and active cienegas have experienced relatively uniform patterns of change that are highly correlated with annual precipitation patterns of the study region. This study results in a more complete inventory of the location and geographic extent of historical cienegas, as well as a better understanding of the variables that can be used to identify different succession paths of cienegas and possible undocumented active cienegas. Additionally, for the first time, the recent trends of change for documented cienegas have been analyzed using remote sensing techniques. This study serves as a preliminary inventory in what should be a series of studies to gain an understanding of the historical and paleodynamics of cienegas, as well as possible restoration opportunities across a larger geographic area. |
