Medusahead (Taeniatherum caput-maedusae) is an annual grass native to the Mediterranean basin that has been introduced to Chile, Australia, and the US where it comprises a major threat to biodiversity through direct competition and alteration of ecosystem structure and function. One management approach that has received little attention is timed mowing to interrupt seed development in medusahead. In a randomized block field experiment I evaluated the effects of timed mowing (control, mowed once, mowed annually) on medusahead abundance in subsequent years and the survivorship of native propagules under these mowing treatments. I measured percent cover of all species based on visual estimation in 1 m² at the end of each growing season prior to mowing. After two growing seasons, I introduced seedlings of native perennial grasses and forbs to the center 1 m² of all plots in half of the blocks and their survivorship was measured at three times over the growing season. Medusahead cover and native seedling survival were analyzed using the mixed model ANOVA procedure with repeated measures in SAS 9.1.

Results/Conclusions

Both mowing (F_2,27=7.95, p=0.002) and time (F_2,53.7=99.22, p<0.001) significantly affected medusahead cover. Medusahead cover decreased over time in mowed plots more than control plots (mowing x time interaction F_4,53.7=3.47, p=0.014).  There was no difference in first year survival of native forbs or grasses between the different mowing levels but both decreased over time across mowing levels (F_2,24=48.22, p<0.001). These findings demonstrate that mowing can be an effective tool for reducing medusahead abundance but has no effect on survival of native seedlings during their first growing season.