Blue Oak The blue
oak is native to the state of California on the
western coast of North America. In its natural
habitat it grows in the valleys and lower slopes of
the Coast Ranges, the lower western foothills of
the Sierra Nevada, and the north slope of the San
Gabriel Mountains. Blue oak covers about 3 million
acres and is one of the largest ancient forest type
in California. The Scottish biologist David
Douglas first named the blue oak in 1831 for the
bluish color of its leaves. The habitat
of blue oaks is open Blue oaks are adapted to drought and dry climates. They can survive temperatures above 100° F for several weeks at a time. Average maximum temperatures in July can range from 70° to 100° F. In January minimum temperatures can range from 10° to 35° F. Annual precipitation averages 20 to 40 inches and mostly falls in the form of rain. The blue oak is a short tree with an open canopy. The canopy is typically rounded with many crooked branches. The tree grows to average heights of 30 feet. In deep, moist soil it can grow up to 60 feet. It is a winter deciduous tree, but will sometimes shed its leaves during severely hot and dry years and go dormant. The litter of leaves and twigs decomposes into a soil high in nutrients and organic matter, holding water better than the surrounding areas. This contributes to high species diversity under the canopies. Leaves of
the blue oak are simple and grow alternately on the
twig. The leaves are about 1-3 inches long and
have wavy, shallow and irregular margins, usually
with 7 lobes. They have a blue-green color above,
and yellow-green on the lower surface. A waxy
coating covers the tough and thick leaves to help
conserve water. Male
flowers are yellow-green catkins. Female flowers
are small and often solitary. These grow in the
axis of the leaves on new twigs. Blue oaks flower
from April through May. The blue oak has an extensive root system. It can grow through cracks in rocks to depths of 80 feet to reach ground water. Its root system allows it to survive in fire prone and arid regions. Blue oaks reproduce both through seeds and vegetatively from burnt or cut stumps. The light colored bark is thick and helps reduce fire damage. The blue oak isn't used in manufacturing because of its crooked growth habit. But it is used as fence posts and fuel wood. Native Americans made meal from blue oak acorns, and used the acorn leachate for dying baskets. The wood was used to make bowls. Stands of blue oaks are typically 80 to 100 years old. Blue oaks are slow growers, and small plants can be 25 years old. Some blue oaks are as old as 200 to 500 years old. The number of blue oaks has decreased because there has been no natural regeneration. It is not considered endangered, however, because of its wide distribution across the region.
bibliography: Howard, Janet L. "Quercus douglasii", U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (2002, September). Fire Effects Information System, [Online]. Available: http://www.fs.fed.us/database/feis/ [Dec. 2002]. "CNPS - Hardwood Woodlands", http://www.cnps.org/forestry/hardwoods/ "Quercus douglasii fact sheet", http://www.cnr.vt.edu/dendro/dendrology/syllabus/qdouglasii.htm "Biogeography of Blue Oak", http://bss.sfsu.edu/geog/bholzman/courses/fall99projects/blueoak.htm
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