Acorns are the ultimate source of regeneration for oaks (Quercus spp.) and are an important food source for many species of vertebrate and invertebrate wildlife. We conducted visual counts as an index of blue oak (Q. douglasii), coast live oak (Q. agrifolia), and valley oak (Q. lobata) acorn production in San Benito, San Luis Obispo, and Santa Barbara Counties, California, during 1988-1997. Mean mast score of all species combined was highest in Santa Barbara County and lowest in San Luis Obispo County (P = 0.004). Mean mast scores did not differ among species (P = 0.064), but scores were highest for valley oak and lowest for blue oak. Mean mast scores differed widely among years (P <0.001), but did not correlate well among counties or oak species. Open canopy trees had higher (P 0.001) mean mast scores than trees suppressed by other canopy trees. Mast scores were weakly and inconsistently correlated with total annual precipitation and average March-April temperature. Differences in acorn abundance among years and counties likely can be attributed to climatological differences (temperature, wind speed, precipitation) among counties and at micro-site locations.
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