For at least a century, scientists have been concerned that some of California's 20 native oak species are not regenerating adequately, especially in the state's 10 million acres of oak habitat that are grazed by cattle.

In the October-December 2005 issue of the University of California's California Agriculture research journal, scientists with the UC Integrated Hardwood Range Management Program review two decades of research concerning the regeneration of oaks in California rangelands.

Douglas McCreary, natural resources specialist at the UC Sierra Foothill Research and Extension Center, and Mel George, rangeland management specialist at UC Davis, conclude that while "livestock grazing is a principal factor in poor oak regeneration in California," land managers can promote oak regeneration by "physically protecting seedlings and managing stock densities and grazing seasons."

The article reports on a series of studies in the Sierra foothills which showed that cattle will indeed graze on oak seedlings, in particular during times of the year when grass is less plentiful or when high densities of cattle are allowed to graze in a certain area. Other trials confirmed that excluding cattle from oak woodlands allows more oak seedlings to grow.

Further studies found that seedlings in grazed woodlands can survive and thrive if protected by simple, inexpensive tree shelters - rigid plastic tubes placed over individual seedlings. If seedlings are protected until they reach a threshold height of 6.5 feet, "oaks may [then] be large enough to withstand cattle damage in lightly to moderately grazed pastures and continue growing," McCreary and George wrote.

The peer-reviewed review article is posted in full online at http://californiaagriculture.ucop.edu. The article includes grazing management guidelines to help reduce the risk of damage to oak seedlings.



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, call (510) 987-0044 or write to calag@ucop.edu. For a printed copy of California Agriculture, media should e-mail janet.byron@ucop.edu or call (510) 987-0668.

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