| I investigated the effects of season and frequency of mowing on prairie communities in north-central Oklahoma by conducting experiments on two sites, an annually mowed hay meadow (Lake Carl Blackwell, LCB) and a lightly grazed pasture (Veterinary Medicine Ranch, VMR). At LCB I reversed the prior mowing regime by stopping mowing. On the previously unmowed VMR, I initiated a factorial experiment with all possible combinations of March, June and September mowing treatments.; Mowing during any season increased species richness at VMR, while species richness decreased when mowing stopped at LCB. Treatments with multiple mowings per year had the highest richness although the additive effect was not always significant. Annual forbs experienced the greatest change in species richness with changes in mowing regimes. In addition to mowing, I identified increased spring and fall light levels, precipitation and the presence of Bothriochloa ischaemum (L.) Keng as important factors which influenced species richness.; I used multivariate statistics to investigate changes in species composition on the sites. A Detrended Correspondence Analysis (DCA) on the pretreatment data separated the two sites. Three years after altering the mowing regimes the two areas remained different with several species unique to each site. Mowing promoted higher forb cover and frequency at both sites. However, annual forbs decreased quickly on LCB with the cessation of mowing whereas perennial forbs increased in cover.; I used a series of partial Redundancy Analyses (pRDA) to investigate the effects of different seasons and frequencies of mowing at VMR. The mowed treatments became more distinct from the control as the study continued. The March- and September-mowed treatments tended to be more similar than the June-mowed treatments. The effects of the March and September mowing, and those of the June treatment following a drought, suggest that early spring light level was an important factor influencing species composition. |
