Pacific Southwest

Title: Historical Mortality of Valley Oak (Quercus lobata, Nee) in the Santa Ynez Valley, Santa Barbara County, 1938-1989

Author: Brown, Rodney W.; Davis, Frank W.

Date: 1991

Source: In: Standiford, Richard B., tech. coord. 1991. Proceedings of the symposium on oak woodlands and hardwood rangeland management; October 31 - November 2, 1990; Davis, California. Gen. Tech. Rep. PSW-GTR-126. Berkeley, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 202-207

Station ID: GTR-PSW-126

Description: The range and abundance of valley oak (Quercus lobata, Nee) have steadily decreased in the last 100 years due to low rates of regeneration during this period. Documented low rates of sapling recruitment must be compared to adult mortality rates in order to evaluate the severity of this decline. The purpose of this research is to measure and analyze the mortality rate of established valley oaks in different habitat types over the past 51 years. Valley oak stands of the Santa Ynez Valley in Santa Barbara County were mapped and stratified into three major habitat types: valley floor alluvium, lower hillslopes and swales, and rolling uplands. Mortality rates of canopy individuals in each habitat type were determined for a sample of 600 valley oaks censused in 1938 aerial photography and re-censused in 1954, 1967, 1978, and 1989. 125 of 600 (20.8 percent) sampled individuals disappeared during the 51 year period. No new individuals were recruited into the canopy layer during this time. The average mortality rate between 1938 and 1989 was 0.45 deaths/100 trees/year. Mortality rates were highly variable within and among habitat types, and were not strongly associated with precipitation or human population increases in the Santa Ynez Valley during the study period. High mortality between 1967 and 1978 coincides with the lowest groundwater levels in the 51 year study period.

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Citation

Brown, Rodney W.; Davis, Frank W.  1991.  Historical Mortality of Valley Oak (Quercus lobata, Nee) in the Santa Ynez Valley, Santa Barbara County, 1938-1989.   In: Standiford, Richard B., tech. coord. 1991. Proceedings of the symposium on oak woodlands and hardwood rangeland management; October 31 - November 2, 1990; Davis, California. Gen. Tech. Rep. PSW-GTR-126. Berkeley, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 202-207.