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Summary1. Hydroperiod, wetland size and land use of watersheds surrounding wetlands have important individual influences on plant communities in wetlands. Our objectives were to determine the effect and relative importance of local and landscape factors on plant species richness, diversity and composition of different functional groups (i.e. total, wetland-dependent, perennial, annual and exotic species) in recently inundated playa wetlands. 2. We surveyed plant communities in 80 wet playas in the Southern High Plains, USA, and measured local factors: water depth, playa volume loss, sediment depth and playa area. We included landscape variables within 3 km: number of playas, edge density, percentage urban area and percentage Conservation Reserve Program area (CRP; conversion from highly erodible cropland to mostly introduced perennial grassland). We also recorded dominant land use as native grassland or cropland. 3. Water depth negatively influenced all plant community metrics (i.e. richness, diversity and cover) while playa volume loss (sediment eroded from watershed filling the basin) had a negative influence on total, wetland-dependent and perennial richness and cover. Playas with more cropland within their watersheds had greater annual and exotic richness and cover, suggesting that agricultural activities within playa watersheds have changed plant composition and facilitated biological invasion. 4. Playa area was less important in predicting plant community metrics in playas. Although not as dominant as local variables, edge density had a positive influence on species richness. Other landscape factors such as number of playas, percentage urban area and percentage CRP area were less important and consistent among different plant community metrics. 5. Synthesis and applications. Our results show that continued unsustainable sedimentation will result in loss of perennial species and promotion of exotic and annual species in playas. Watershed management to limit unsustainable sedimentation has the potential to maintain original playa plant communities dominated by perennial ⁄ native species and should also reduce the loss of playa functionality.

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Playa wetlands in the Southern High Plains provide services such as stormwater storage, groundwater recharge, and biodiversity provisioning. However, watershed erosion has negatively impacted these services. Previously, we demonstrated that water loss rate was influenced by land use variables such as watershed cultivation (tilled index) and playa volume loss (hydric soil defined wetland volume). Because non-anthropogenic water loss in playas is limited to evaporation, transpiration, and infiltration processes, our objective was to determine the impact of wetland vegetation characteristics and land use variables on water loss rate in playa wetlands. We recorded water levels of 70 playas through the summers of 2003 and 2004 and determined the relationship between water loss rate and predictive variables including local playa characteristics, vegetation (structure and cover of functional groups), bi-weekly starting water levels, and watershed soil texture. Playa volume loss was a positive predictor of water loss rate, suggesting infiltration may be greater in playas with more sediment. Water loss rate was lower in playas in the fine-textured zone, but was not influenced by wetland vegetation. To complete quantification of the hydrologic budget of playa wetlands, future studies should focus on the influence of sedimentation on infiltration and recharge.

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