The authors believe that much larger exclosures, such as the 16-foot-by-16-foot fences evaluated in a previous study, are less effective. While they exclude grazing animals, they also encourage dense groundcover that serves as habitat for small rodents. The rodents eat the seedlings’ bark and kill or severely stunt their growth.

“We did not observe any rodent girdling of seedlings in the study of two-foot and four-foot exclosures, apparently because there was not sufficient groundcover in the smaller exclosures for good rodent habitat,” says lead author Ralph Phillips, retired range/natural resources and livestock advisor for UC Cooperative Extension in Kern and Tulare counties.

For the past century, there has been growing concern that natural regeneration rates may be inadequate to sustain tree populations in California oak woodlands, due to grazing, competition from nonnative plants and other factors. There are about 10 million acres of oak woodlands in California; much of this unique habitat does double-duty as rangeland and four-fifths is privately owned. More than 30,000 acres per year of oak woodlands are currently being converted to other uses, such as agriculture and housing.

“Oak woodlands provide critical habitat for California native species,” says Douglas McCreary, a UC oak regeneration expert and former director of the Integrated Hardwood Range Management Program (IHRMP). Over the past 20 years, the UC program has focused on encouraging stewardship of oak woodlands as functioning ecosystems (http://danr.ucop.edu/ihrmp). The state’s oak woodlands provide critical habitat for California native species, including 2,000 plants, 5,000 insects, 80 amphibians and reptiles, 160 birds and 80 mammals.

“IHRMP supports research into best practices to manage grazing in oak woodlands, while maintaining this important ecosystem,” McCreary says. “The program publishes practical guidebooks and offers workshops for landowners, planners and policymakers who have an interest in preserving oak woodlands.”

Another peer-reviewed study in the January-March 2007 issue of California Agriculture found that older blue oak seedlings — monitored by the UC researchers for seven years — are much more likely to survive than those that have just sprouted.

“Once a seedling survives approximately a decade and becomes established, it is much more likely to remain alive than newly germinated seedlings,” Phillips says.

The January-March 2007 issue of California Agriculture journal also features news coverage about efforts to preserve California oak woodlands, experimental treatments to control sudden oak death, and the expansion of research into E. coli contamination of lettuce and spinach. In addition, the current issue includes peer-reviewed research on:

• The Coyote Lure Operative Device, a more-humane method for controlling problem coyotes.
• A survey of integrated pest management (IPM) use by California cotton growers.
• The relationship between early spring temperatures and harvested peach sizes.
• The use of quality-control evaluations to assess farmworker abilities.
• The Nutrition Competencies, new guidelines for teaching nutrition in California schools.

California Agriculture is the University of California’s peer-reviewed journal of research in agricultural, human and natural resources. For a free subscription, go to: http://CaliforniaAgriculture.ucop.edu, write to calag [at] ucop [dot] edu or call (510) 987-0044. For a printed copy of California Agriculture, media should e-mail janet [dot] byron [at] ucop [dot] edu or call (510) 987-0668.

CONTACT: Janet Byron, (510) 987-0668, janet [dot] byron [at] ucop [dot] edu