Effects of shade and simulated herbivory on seedling emergence, survival and growth of two California oaks: Coast live oak (Quercus agrifolia Nee) and blue oak (Quercus douglasii Hook and Arn.)

This study investigated seedling emergence, survival and growth of coast live oak (Quercus agrifolia Nee) and blue oak (Quercus douglasii Hook & Arn.). Recent surveys conclude that regeneration of both species is insufficient to maintain existing stands. Since the 1940s oak habitats have been substantially reduced through conversion to agriculture, housing and industrial uses. Loss of.5 million acres is projected over the next two decades, further reducing biological diversity.;Research took place at UC Hastings Reservation, Monterey County, California, from 1989 to 1991. A split-plot, multifactorial design was implemented within three fenced exclosures testing whether seedlings could establish in annual grasslands away from tree canopy and if species differed in their responses to shade and clipping treatments. Shade was created by shadecloth tarps. There were two levels of clipping treatments, moderate and heavy. Locally collected acorns were planted (n = 2880). Seedlings were not irrigated or fertilized.;Even under conditions of prolonged, severe drought coast live and blue oak seedlings survived in annual grasslands, although patterns of growth and survival would probably have been different under wetter conditions.;Emergence of coast live and blue oak seedlings differed significantly in Year 1, and yearly survival and growth also differed (p ;Seedlings benefited from the shade treatment. Only shaded coast live oak seedlings survived in Years 2 and 3 (p ;Clipping treatments resulted in greater mortality among coast live than blue oak seedlings. This suggests that coast live oak experiences a critical period when it does not sprout vigorously and is vulnerable to both desiccation and herbivory. Many blue oak seedlings sprouted after clipping and survival may have been enhanced by moderate clipping levels.