PARENT SESSION
Oral Session #64: Plant Population Ecology.
Presiding: S. Collins
Wednesday, August 7. 1:00 PM to 4:45 PM. Gila Meeting Room, TCC.

Factors limiting recruitment in valley and coast live oak.

Tyler, Claudia^*,1, Mahall, Bruce¹, Davis, Frank¹, ¹ University of California, Santa Barbara, CA

ABSTRACT- Oak woodland and savanna habitats, among the most diverse communities in North America, have suffered significant losses in the past century. In addition, natural regeneration of the oaks in these systems, appears to be insufficient to maintain current populations. The relative importances of factors that may be responsible for this lack of regeneration are not clearly understood. We have replicated large-scale planting experiments in four different years, to determine the effects of cattle and other ecological factors on seedling establishment of valley oak (Quercus lobata) and coast live oak (Q. agrifolia). In 33 large experimental plots (50 x 50 m) we planted acorns from Q. lobata and Q. agrifolia. Fifteen of these large plots are controls, open to grazing, fifteen exclude cattle with the use of electric fence, and three are ungrazed in large ungrazed pastures. Within the plots, experimental treatments included: 1) protection from small mammals, 2) protection from large animals, and 3) no protection from mammalian grazers. In winters 1997, 1998, 2000, and 2001, we planted approximately 1000 acorns of each species. Results confirm that seed predation and herbivory by small mammals are a significant "bottleneck" to oak seedling recruitment on the landscape scale. Comparing results among years indicates that lack of late winter rainfall can significantly reduce oak emergence and establishment. Survivorship of protected acorns and seedlings is comparable in grazed and ungrazed areas.

KEY WORDS: Quercus, grazing, seedling, recruitment