Medusahead dispersal and establishment in sagebrush steppe

Medusahead (Taeniatherum caput-medusae (L.) Nevski) is a nonnative, winter-annual grass that reduces biodiversity and production of rangelands.  To prevent medusahead invasion land managers need to know more about its invasion process.  Specifically, 1) when and how far medusahead seeds disperse and 2) establishment rates and interactions with preexisting plant communities.  Medusahead seed dispersal from invasion fronts were measured using sticky seed traps along 23, 35-m transects.  Medusahead establishment was evaluated by introducing medusahead wildrye at 1, 10, 100, 1000, 10 000 seeds*m^-2 at 12 sites.  Most medusahead seeds dispersed less than 0.5 m from the infestation (P < 0.01) and no medusahead seeds were captured in the traps beyond 2 m from the infestations.  Medusahead seeds dispersed from the parent plants from early July to the end of October.  More seeds were trapped in August than the other months (P < 0.01).  Medusahead establishment increased with higher seeding rates (P < 0.01).  Medusahead density was negatively correlated to tall tussock perennial grass density and positively correlated to annual grass density of the preexisting plant communities (P = 0.02 and 0.02, respectively).  Medusahead cover was also negatively correlated with the tall tussock perennial grass density (P = 0.03).   Our results suggest that containment barriers around medusahead infestations would only have to be few meters to be effective.  This study also suggests promoting tall tussock perennial grass in areas at risk of invasion can reduce the establishment success of medusahead.