The widespread invasion of California’s Mediterranean-type annual rangelands has led to declines in the multiple benefits society derives from these working landscapes. It is imperative to find successful strategies for managing weedy invasives in these complex socio-ecological systems while adapting to a changing climate—which is expected to bring increasing frequency, severity, and durations of drought. Our three-year investigation focused on testing the response of Taeniatherum caput-medusae and other invasive weeds, pasture productivity, animal productivity, and species richness to three stakeholder prescribed grazing management strategies: season long continuous, fall-spring with winter rest, and fall-spring targeted grazing. We deployed an extensive permanent grid of 8 plots per hectare across three grassland pastures (~50 ha each) and three oak woodland pastures (~80 ha each). This allowed for spatial and classical analysis of treatment effects.
We found a reduction in T. caput-medusae cover ranging from 15% to 25% across all treatments, while no reduction was observed in the ungrazed controls. Through a spatial analysis utilizing natural neighbor interpolation we found targeted grazing reduced and nearly eliminated patches of T. caput-medusae dominated communities (defined as >50% cover). We also found the potential capacity to adapt to drought and available forage was greatest within the targeted grazing treatment pastures, which was potentially due to increased forage harvesting efficiencies. Animal productivity was greatest in the fall-spring treatment; however, the season long continuous and fall-spring targeted treatments were not significantly different from each other in terms of livestock average daily gain. This highlights the opportunity that agricultural production goals on working landscapes could be compatible with invasive species reduction strategies and enhancement of the quality and quantity of ecosystem services supplied from these systems. The results of this study will help land managers and producers in decision making for drought adaptation, enhancing richness, and invasive weed management.