Plant Species Impact the Suite of Ecosystem Services Provided Seasonally in California's Grasslands.

California’s grasslands have been dominated by annual exotic grasses for the past 200-300 years. More recently, newer invasive grasses have become prevalent, such as medusahead and barbed goatgrass. Control of these newer invasive grasses, or restoration of natives is not possible in all impacted areas, due to the broad extent of these invasions.  Ecosystem services are a potential criteria to prioritize areas for restoration and weed control .  We planted plots consisting of three community types: naturalized exotic species (that have dominated California’s grasslands for 200-300 years), invasive weeds (goatgrass and medusahead), and native species (common mix of species used for restoration in California’s Central Valley).  After 3 years, we assessed the impacts of these vegetation types on multiple ecosystem services. When comparing natives to naturalized species, natives increased soil nitrogen availability, and were much better at suppressing invasive weeds. However, the naturalized species plots provided better erosion control, mitigation of soil compaction, water quality, and soil water storage.  This suggests that restoration of natives will be most beneficial in areas with high invasive weed pressure, but could be detrimental in areas where erosion, compaction, and water quality are of concern.  Invasion of noxious rangeland weeds into the naturalized community did not enhance any ecosystem services, and greatly decreased palatable spring forage quantity. However, there is a tradeoff between invasive weeds and native species.  Invasion of noxious weeds into native communities decreased spring forage availability and decreased soil nitrogen availability, but enhanced soil water storage, compaction alleviation and water quality. This suggests that sites that are less vulnerable to soil degradation would be best to prioritize for invasive weed control.  While the impacts of invasive grasses on California’s flora are an important criterion for restoration and weed control, it is not possible to manage all invaded areas. Thus, prioritization of sites for management should consider that some of these invasive grasses are improving soil conditions and water quality.