California grasslands are being invaded by annual grasses that rapidly reduce diversity. Restoration in this system focuses on re-establishing native perennial bunchgrasses to increase diversity and provide resistance to invasion through priority effects. However, the high cost of native seed limits the extent of restoration efforts.
Strip seeding is a proposed cost-effective method where native seeds are sown in rows with unseeded areas between them. The sown species then colonize the unseeded areas over time. However, the method leaves unseeded areas vulnerable to invasion. If invaded, management techniques are needed to control the invasive species and maintain established native perennial stands. We examined whether two management techniques, prescribed burning and targeted sheep grazing, within a strip seeded area 1) reduced cover of Elymus caput-medusae (medusahead), an invasive grass, 2) had limited negative effects on seeded grasses and, 3) facilitated spread of seeded grasses to unseeded areas.
To simulate invasion, we seeded medusahead into unseeded areas of 5-year old experimental strip seed plots. Starting a year later, we applied targeted grazing and small-scale prescribed burns, alone and in combination, for 3 years. We measured community composition in unseeded areas to determine the effects of treatments on medusahead and perennial grass cover.
Results/Conclusions
We found that all combinations of grazing and burning (graze only, burn only, and graze plus burn) significantly reduced cover of medusahead over time, while there was no change in medusahead cover in the control plots. There was no change in native perennial grass cover in the control treatment and the burn only treatment, but perennial grass cover decreased over time in both treatments that included grazing (graze only and graze plus burn). There was no evidence that either grazing or burning facilitated spread of perennial grasses to unseeded areas.
While both prescribed burning and targeted grazing are effective control methods for medusahead, tradeoffs exist for native cover when using grazing, at least in the short term. Perennial grasses are still abundant at the site and may be able to recover with grazing exclusion. Although native perennial grass cover was not affected by burning, in practice, tradeoffs also exist with prescribed burns due to concerns about safety and liability. This study demonstrates the complexity of managing multiple restoration goals as various effective methods have different tradeoffs that must be considered for informed management.