Inter- and Intra-specific Interactions in Germination and Seedling Establishment of Cheatgrass and Russian Wildrye

Cheatgrass (Bromus tectorum) is an invasive species in the arid and semi-arid west of the USA, and is weedy in disturbed prairie landscapes. Perennial Russian wildrye (Psathyrostachys juncea) limits population growth of cheatgrass, but the mechanism is unclear. I conducted glasshouse and greenhouse experiments to test if intra- and interspecific competitive interactions of seeds and seedlings of cheatgrass and Russian wildrye were different across a geographic soil gradient with different cultivation legacies in eastern Montana, USA. Seed-seed interactions occurred in both species. Cheatgrass and Russian wildrye inhibited one another’s emergence in one edaphic condition in one experiment. Cheatgrass growth was less inhibited by Russian wildrye than by intraspecific neighbors. It appeared that cheatgrass was more sensitive to environmental conditions such as edaphic conditions and intraspecific competition than Russian wildrye. Understanding how environmental conditions prevent cheatgrass emergence is a key aspect of controlling cheatgrass invasion