Blue Oak Regeneration in Southern Sierra Nevada Foothills1

A survey of blue oak stands in four southern Sierra areas indicated there was a substantial number of seedlings and mature trees, but there were considerably fewer trees in the sapling and pole size class. These differences prompted a long-term survival study. After 6 years, 68.5 percent of the trees were still present and had grown 0.02 inches. A study of aging seedlings showed that the percentage of seedlings less than 10 years old ranged from 52.7 percent to 98.4 percent for the three sites. More than 10 percent of the seedlings in one site were more than 25 years old. A 2-year study evaluating acorn quality showed that acorns from Madera County had a faster and higher emergence rate than acorns from Kern County. The Southern Sierra Hardwood Range region, consisting of Madera, Fresno, Tulare, and Kern Counties contains almost 1.5 million acres of hardwood rangeland. Eighty percent of this land is privately owned, and blue oak (Quercus douglassii) is the most abundant oak species. Obtaining adequate natural regeneration to maintain current stands of blue oak is of concern for some landowners, government agencies, and conservationists. Studies were conducted to evaluate regeneration factors such as blue oak size classes, acorn quality, and natural seedling survival. These studies have been carried out over the past 9 years to better understand the biology of blue oaks growing under natural conditions. Data were analyzed using an analysis of variance and differences between means were determined using Duncan Multiple range. Significance is expressed as P ≤ 0.05. A Survey of Blue Oak Height Classes in Madera, Fresno, Tulare, and Kern Counties In 1987, a preliminary survey was conducted in Kern County to inventory the population and height classes of blue oaks. The following year the survey was expanded to include Tulare, Fresno, and Madera Counties. Regeneration transects were established in each of the four counties, beginning at low-elevation and open blue oak savannas. The oak-covered hardwood rangeland began at an elevation of about 600 feet in the northernmost transects of Madera County, and about 1,600 feet in the southernmost transects of Kern County. Annual rainfall at these low elevations averaged 10-15 inches (table 1). The elevational transects passed through the hardwood range sites heading uphill, generally west to east, until they reached the transition between hardwood range and mixed conifer forest at elevations of 3,000 feet in Madera County to 4,800 feet in Kern County. Fourteen to twenty regeneration survey plots were located at random in patterns radiating out from each of the four elevational transects. Random plot locations were checked to ensure that they occurred in the blue oak woodland vegetation type. If a plot did not match the blue oak hardwood type, another location was randomly selected. Plots were located exactly 200 feet to the north or south of the main elevational transect. Altogether, 68 plots were sampled for this study. Each sample location was a strip transect 100 feet long and 12 feet wide (0.028 acres). Trees were classed as seedlings (trees less than a foot tall), 1An abbreviated form of this paper was presented at the Symposium on Oak Woodlands: Ecology Management and Urban Interface Issues, March 19-22, 1996, San Luis Obispo, Calif. 2Range/Natural resources advisor, University of California Cooperative Extension, 1031 S. Mt. Vernon Avenue, Bakersfield, CA 93307. 3Natural resources specialist, University of California Cooperative Extension, 328 Madera Avenue, Madera, CA 93637. 4Program manager and specialist, Integrated Hardwood Range Management Program, University of California Cooperative Extension, University of California, Berkeley, CA 94720. 5Natural resources specialist, University of California Cooperative Extension, U.C. Sierra Foothill Research and Extension Center, 8279 Scott Forbes Road, Browns Valley, CA 95918. 6Area natural resource advisor, University of California Cooperative Extension, 311 Fairlane, Placerville, CA 95667.