Most native vegetation in North American grasslands evolved under significant pressure from ungulates and other herbivores. With the expansion of human influence, many native ungulates have been replaced with domesticated ones, and these species continue to play substantial roles in shaping grassland dynamics across the country. Thus, effective management of herbivores is often a key determinant of successful maintenance of native biodiversity, forage provisioning and other ecosystem services. Here we discuss the effectiveness of coupling local understanding of herbivore-grassland interactions with scientific analysis at multiple scales to evaluate optimal management strategies for ecosystem service protection in the face of environmental variability. The case study we provide describes ten years of collaborative research with land managers in a working grassland landscape in California, where plant community diversity and function is threatened by invasive noxious weeds. In this project, we have used remote sensing and field experiments to test ideas about rangeland restoration that the stakeholders themselves have generated. Remote sensing imagery allows land managers and scientists to jointly evaluate forage provisioning services, weed patch dynamics, and the effects of native grass establishment over time under different management regimes.
Results/Conclusions
Through this integrated process, we found that fall grazing of senesced vegetation—a strategy suggested by ranchers themselves—was more effective at promoting valued plant species and reducing weed proportions than the more commonly employed spring grazing. With time series analysis of aerial imagery, we mapped fine-scale vegetation patches and quantified those that formed, dissolved, or remained constant over time as a function of environmental factors and management strategies. Ranchers related these analyses to their management practices in order to make real-time adjustments to grazing strategies to improve forage provisioning and weed control. Field measurements of patch properties revealed that late-season use of water by weeds was reduced by the presence of early-season forage grasses. In mixed patches, spring grazing favored weeds by reducing forage cover and increasing water availability. The principles employed here—active collaboration between managers and scientists, incorporation of local knowledge in experimental design, multi-scale time series analyses—are highly relevant to efforts to protect ecosystem services across many ecosystem types. Continued collaborative experimentation to support adaptive management of ecosystem services will likely be necessary as climate change and human population impacts intensify.
