Physical loss and modification of Southern Great Plains playas.

Playas are the primary wetland system in the Southern Great Plains (SGP) of North America providing critical stopover habitats for migratory birds in the Western Hemisphere. Collectively, these wetlands form the keystone ecosystem in this region supporting biodiversity for North America and provide habitat for native plants and animals that are essential for maintenance of international biological diversity along with other local and regional ecological services. Large-scale landscape changes in this region, primarily as a result of agriculturally-based anthropogenic impacts, threaten playas with functional loss and physical extinction. These impacts are not considered in current estimates of the number of extant functional playas, leading to biased estimates by groups or agencies extrapolating research or monitoring results, conducting conservation planning, and modeling impacts of future climate change. Using a combination of stochastic and empirical data, we identified impacts to playas and playa watersheds and quantified the extent and rate of these impacts relative to physical loss. Only 0.2% of playas had no wetland or watershed modification and we conservatively estimate that 17% of playas recently existing on the landscape no longer are represented by an apparent depression. With the inclusion of sediment volume estimates where ≥100% of the volume of original differentiated playa soil has been filled, 60% or 16,855 playas have been physically lost from the SGP despite a continued presence of a depression. Data also show that small playas are being lost more rapidly than larger ones; the average size (±SE) of extant playas has increased from 7.5 ± 0.47 to 8.5 ± 0.55 ha. The reduced ecological condition of 95.3% of playas remaining on the landscape exceeds historical predictions of a maximum 85% of playas ever being modified. Given the results of this study these changes can now be accounted for, resulting in more informed management and conservation of playas and bring awareness to the urgency of implementation of effective conservation measures for playas and the species that depend on this keystone ecosystem.