Selected Ciénega and Surrounding Floodplain Polygons of the Greater Madrean Archipelago Ecoregion

Ciénegas are freshwater to brackish wetlands in arid and semi-arid regions of North America, although they are primarily found in the southwestern U.S. and northwestern Mexico at elevations usually below 2000 meters. They are associated with groundwater or actively moving fresh water that historically resulted in perennial surface waters persisting for decades to centuries. The extent of these wetland communities has greatly diminished since European settlement and ciénegas are now considered imperiled, threatening the flora and fauna that rely on these unique water sources. For this study, 31 ciénegas from a “Spatial Database of Known and Potential Ciénegas in the Greater Madrean Archipelago Ecoregion” (Middleton et al., 2022) in the U.S. were mapped using manual digitization, automated image classification and sophisticated filtering techniques on current and historical National Agriculture Imagery Program (NAIP) aerial imagery. The polygons in this database represent both the ciénega and its surrounding floodplain environment to account for changing groundwater and potential influence on vegetation. Although the ciénega is depicted as the core of the wetland, the surrounding floodplain with trees and non-wetland species is included as it may have once been part of the former ciénega. Open water was carefully mapped and excluded from the final polygons, so that estimates of vegetation indices (NDVI and NDII) through time would not be as affected by changing water signatures. Control polygons generated from buffering the ciénega polygons (by 90 and 180 meters) are also included to compare relative change.