Quercus douglasii, known as blue oak, is a species of oak endemic to California, common in the Coast Ranges and the foothills of the Sierra Nevada. It is California's most drought-tolerant deciduous oak, and is a dominant species in the blue oak woodland ecosystem. It is occasionally known as mountain oak and iron oak.
Description
Quercus douglasii is a medium-sized tree with sparse foliage, generally tall, with a trunk in diameter at breast height. The tallest recorded specimen was found in Alameda County, at . The trees grow slowly, about per year. Individual trees over 500 years old have been recorded.
The bark is light gray with many medium-sized dark cracks. The blue-green leaves are tough and leathery,
Taxonomy
The species is one of over 80 named after Scottish botanist David Douglas. The common name "blue oak" derives from the dark blue-green tint of its leaves. (subgenus Quercus, section Quercus).
Ecology
Q. douglasii prefers dry to moist soil and plenty of sunlight. and is also found with interior live oak (Q. wislizeni), coast live oak (Q. agrifolia), valley oak (Q. lobata), Oregon white oak (Q. garryana), Natural hybrids between Q. douglasii and the related Q. lobata, Q. garryana, or Q. john-tuckeri.
The acorns are eaten by wildlife and livestock.
Drought tolerance
Quercus douglasii is the most drought-tolerant of California's deciduous oaks. It has a smaller canopy than less drought-tolerant relatives, and invests proportionally more growth into roots rather than leaves throughout its life cycle. at more than 50. The wasps trigger the formation of oak galls in a wide variety of shapes, colors, and sizes. Native Californians commonly gathered the acorns, which they considered good-tasting, and processed them into acorn flour. They made baskets out of blue oak seedlings, utensils such as bowls from the wood, and dye from the acorns. Commercially, the blue oak is mainly limited to use as firewood.