Seed persistence of an introduced and a native grass species in a prairie old field.

摘要

While Agropyron cristatum is useful in the agricultural industry for grazing and hay production, it prevents successful revegetation of old fields with native species. I determined the persistence of seeds of an introduced (Agropyron cristatum) and a native grass ( Bouteloua gracilis) species with and without neighbour removal at two water levels. Neighbours were controlled with glyphosate application in May of 1994--7. Water was added based on rainfall patterns in the single wettest and driest years over the previous 20. Seeds were spread onto the soil surface and germination was measured weekly from April to October. Germination was significantly higher in the high water plots. Final germination was around 20% for both species and there was no effect of neighbour removal. Seeds of both species were also buried in mesh bags 1 cm below the surface of the soil in April and removed in October. Slightly more B. gracilis seeds germinated than A. cristatum. This indicates that A. cristatum may contribute more seeds to the seed bank, than does B. gracilis. In fact, in plots where no seeds were added and neighbours were controlled, up to 2000 seedlings/m2 of A. cristatum were found. This high germination in background plots may be partly explained by the large pool of A. cristatum seeds that probably exist in the soil, and partly by the high seed output of individuals growing in these plots. Landscape scale restoration plans cannot easily address the issue of water availability. As well, the pool of alien propagules may further complicate the efforts as neighbours appear to be important during seedling growth, although not during the germination phase. Complete removal of all neighbours is not easily accomplished with herbicide application, therefore neighbours may affect restoration efforts long after the removal process has begun.