GRAZING EFFECTS ON GERMINABLE SEEDS ON THE FESCUE PRAIRIE

The germinable seed bank in a grassland affects the succession of degr aded range and the recolonization of disturbed sites, and must be unde rstood to predict potential responses to management. The germinable se ed bank on the fescue prairie was characterized and its relationship t o grazing, season, and depth of burial determined, The study was condu cted in the fescue prairie of southwestern Alberta in livestock exclos ures and on paddocks that, since 1949, have been stocked at fixed rate s to achieve light, moderate, or heavy grazing pressures. Surface debr is was sampled in fall and spring, and soil was sampled to a depth of 6 cm in spring. The samples were spread on vermiculite in trays and th e seeds allowed to germinate over a 90-day period. In fall, total surf ace seed numbers m(-2) increased from 1,785 to 7,783 from the ungrazed to heavily grazed site, and most of the differences were accounted fo r by whitlow-grass (Draba spp.) and Kentucky bluegrass (Pea pratensis L.). These species also contributed most to differences between fall a nd spring on the grazed sites. Total seed numbers were similar (1,790 vs 1,803) in spring and fall on ungrazed sites. The species compositio n of the seed bank did not change with depth. In the soil, the annual forb pygmyflower (Androsace septentrionalis L.) was the most common se ed but was not detected in a vegetation survey, Soil disturbance in th e fescue prairie is more likely to lead to a seral community dominated by annual forbs, than a rough fescue (Festuca campestris Rydb.) domin ated grassland.