Much like savanna ecosystems elsewhere in the world, California oak woodlands are home to a mix of trees dominated by blue oak, interior live oak, and foothill pine, scattered across a landscape with an understory of grasses and other herbaceous species. While covering only 6.5% of California’s land area, oak woodlands provide a variety of natural resources. Over 300 terrestrial vertebrates make their home here including California quail, acorn woodpeckers, bobcats and mountain lions. In addition to native wildlife, oak-dominated ecosystems are heavily used for live stock production and contribute 75% of the forage for livestock produced in the state. Oak woodlands also play a major role in our drinking water supply, as most of California’s surface water passes through them as direct rainfall or snow melt from higher elevations.
Early ranching activities to provide charcoal and firewood and to improve forage productivity led to the removal of oak trees and converted large areas into grasslands. Slow natural regeneration of trees has stalled the recovery of woodlands and led to a growing concern about the long term viability of certain oak populations. The understory herbaceous plant community has also undergone the transformation of perennial bunchgrasses to exotic annual grasses that grasslands across the state have experienced during the past 200 years.
Currently, highly invasive noxious weeds such as medusahead and yellow starthistle are negatively impacting the biodiversity of oak woodlands and reducing the economic returns of livestock production by degrading the quality of rangelands. Balancing the long term ecosystem health and management of these working landscapes has been a challenge in this system and a central tenet of our research in rangelands/woodlands.
Our lab is currently exploring several projects in this system. As part of joint effort with Drs. Mitch McClaran and Stan Harpole, we are trying to identify how the timing of grazing can interact with the various life stages of blue oak (Quercus douglasii) to influence its recruitment and establishment. We are also investigating the mechanisms that can trigger pasture-wide invasion of rangelands by noxious weeds and in collaboration with Dr. Scott Stephens potential management tools such as fire to eradicate or control the invaders.