Grazing and Resilience in California Rangelands

Rangeland systems, particularly those in arid and semiarid regions,
exhibit complex dynamics in response to disturbance and climate variation. Substantial shifts in vegetation state – for instance, from acceptable forage to noxious weeds – can occur with little forewarning and, once the shifts occur, they may be difficult to reverse. Incorporating this complexity in the development and evaluation of management frameworks has been a long-standing challenge.

This project examines whether grazing management can change the resilience and threshold dynamics in a California rangeland system. We focus on three ecosystem states that differ in conservation and forage value: perennial native grasslands; annual exotic grassland state dominated by acceptable forage species; and annual exotic grassland dominated by
noxious weeds such as medusahead.

At the Sierra Foothills Research and Extension Center, we are experimentally manipulating grazing intensity to identify critical thresholds where rapid changes in rangeland vegetation and health may occur. We are also investigating how different types of pasture vegetation may promote positive feedbacks with the soil system, creating conditions where vegetation may seem stuck in a particular state regardless of management efforts. This research will provide ways to identify critical thresholds that can stymie sustainable rangeland management and offer tools to retain efficient functioning in rangeland systems.