COMPOSITION OF SEED BANKS ALONG AN ELEVATIONAL GRADIENT IN PLAYA WETLANDS

We analyzed the composition of seed banks dong an elevational gradient (0-1 m) in playa wetlands of the Southern High Plains of Texas. Differing seed-bank composition along such a gradient may be one mechanism in the determination of vegetation structure in wetlands. We used the seedling-emergence technique under moist-soil and submerged treatments to ascertain the composition of seed banks in 8 playas. There were no differences (P > 0.05) in overall or common species seedling densities along the elevational gradient. Fluctuating water levels in a relatively shallow wetland, combined with the short linear distance of the gradient into a flat bottom, results in the uniform distribution of seed in playas. Additionally, wind action during periods when playas are dry may serve to distribute seeds throughout the wetland. Structure of vegetation in playas is determined principally by the varying soil moisture regime, which regulates composition of species germinating when other environmental conditions are suitable. When environmental conditions, including soil-moisture content, are appropriate for germination, each species in the seed bank could potentially be found throughout the wetland. When managing playas for specific plant species through manipulation of soil moisture, we can expect a comparable species response to similar treatments anywhere in the playa.