Impacts of mulch on prairie seedling establishment: Facilitative to inhibitory effects

Abstract

Seedling establishment in semiarid prairie sites under reclamation can be facilitated by mulch due to its effects on seedbed conditions. Effects on plant recruitment can also be inhibitory, as mulch can filter out or attenuate environmental signals that break seed dormancy and can negatively affect early seedling performance. A manipulative field experiment was established to determine if straw and hay mulch facilitate seedling emergence and establishment. The reclamation site is an abandoned irrigation area in the mixed grass prairie of southern Alberta, Canada. Soil was tilled and the seedbed prepared through manual harrowing, then plots were broadcast seeded with Elymus trachycaulus, Bouteloua gracilis, Hesperostipa comata, Astragalus canadensis and Linum lewisii. Hay and straw mulch were applied at two rates (300 and 600gm−2). Seedling emergence and survival were assessed through the first growing season. Both hay mulch rates increased E. trachycaulus and L. lewisii seedling emergence relative to bare ground. A. canadensis seedling emergence was more than ten times higher with low straw and both hay rates than with bare ground. Straw mulch facilitated seedling emergence at a low rate but had a neutral effect at high rates. Effects of low straw and both hay mulch rates on seedling establishment were facilitative for E. trachycaulus and L. lewisii and neutral for B. gracilis. Effects of high straw rates were neutral for E. trachycaulus and L. lewisii and hindered B. gracilis seedling establishment. These results clearly show that low mulch rates can increase native plant establishment during the critical first year of prairie reclamation as they were able to overcome microsite limitations.