The Value of Oak Woodland Habitats as Control for Medusahead (Taeniatherum caput-medusae)

Although medusahead (Taeniatherum caput-medusae) is one of the most dominant invasive rangeland grasses in the West, we know surprisingly little about the environmental factors that drive medusahead abundance. Understanding the conditions that influence spread dynamics is central for developing effective monitoring, prevention and control programs. We established grassland plant communities and added medusahead seed across a range of five densities (from 0 to 50,000 seeds per m) in open grassland and oak savannah habitat. We followed plants throughout the season to understand how habitat and seedbank dynamics affect underlying vital rates and overall density. Oak woodlands reduced medusahead abundance by almost 300 percent, and this effect was greater later in the growing season. The negative effect of oak woodlands was almost an order of magnitude less for common competitive annual species. We also found that reproductive spike production was lower in the oak habitat than the open habitat; and that seeding rate had a negative relationship with seed produced per spikelet. These effects ultimately contributed to a reduction in medusahead reproductive output between habitats, across seeding rates. This work highlights the value of oak woodland habitats as an effective and sustainable way to control medusahead density and recruitment.