|A large Blue Oak in a pasture in Mariposa County, California.|
Hook. & Arn.
Quercus douglasii, the Blue Oak, is an oak in the white oak section of the genus, Quercus sect. Quercus. It is endemic to California and is found in foothills surrounding the Central Valley of California and certain locations in the California Coast Ranges, USA. It is also sometimes known as the Mountain Oak, and occasionally the Iron Oak.
Quercus douglasii, the Blue Oaks, are medium-sized trees growing up to 15–25 m tall, usually with a somewhat irregularly-shaped crown, and a trunk 0.5–1 m in diameter. The tallest recorded oak was found in southern Alameda County, at 94 ft. The bark is light gray with many medium-sized dark cracks; from a distance, it can appear almost white. The name Blue Oak derives from the dark blue-green tint of its leaves, which are deciduous, 4–10 cm long, and entire or shallowly lobed. The blue color can be subtle but becomes much more evident when viewed next to one of the live oaks with whom it shares its range, which tend to have much greener leaves. The acorns are 2–3 cm long, with a moderately sweet kernel, and mature in 6–7 months from pollination. It prefers dry soil and plenty of sunlight.
Individual Blue Oaks over 500 years old have been recorded, although most are less than 300 years old. Recent research has found several unlogged stands of Blue Oak woodlands, suggesting that the state may harbor over 500,000 acres (2,000 km2) of such old growth forests.
Natural hybrids between Blue Oak and the related Shrub Live Oak (Quercus turbinella), Valley Oak (Q. lobata) and Oregon White Oak (Q. garryana) often occur where the species grow together in the same area. Other species sympatric with the Blue oak include Canyon live oak and Pacific madrone.
- C. Michael Hogan, 2008
- Philip M. McDonald, USDA
- Flora of North America
|Wikimedia Commons has media related to Quercus douglasii.|
- Flora of North America: Quercus douglasii
- C. Michael Hogan (2008) Blue Oak: Quercus douglasii, GlobalTwitcher.com, ed. N. Stromberg
- Philip M. McDonald, USDA Forest Service: Quercus douglasii
- Stahle, David. "Ancient Blue Oak Woodlands of California". University of Arkansas Tree-Ring Laboratory. Retrieved 2008-11-10.
- Peterson- Raptors of California