Just for the hell of it, did some research, I wanted to check my own personal knowledge of altitude habitat…I still say it seldom grows above 3000 ft…4000 tops, but…
After a few google hours…
Western poison oak (Toxicodendron diversilobum, Anacardiaceae) - Previously divided into one species called either Rhus Toxicodendron, Rhus quercifolia, Rhus lobata, or Rhus diversilobum. Currently in the Toxicodendron genus - Toxicodendron diversilobum; bush or climbing shrub; west coast US and British Columbia
Poison Oak or western poison oak is native to western North America, with a distribution extending from British Columbia south to the Baja California peninsula. In Washington and Oregon, poison oak- found mainly in the western regions of the states. This western variety found strictly on the Pacific Coast from Southern British Columbia to Baha California. Its range stopped by the deserts and the Sierra and Cascade Mountain ranges to the east and by the Pacific on the west.
The western variety - discovered by the prolific botanist David Douglas (1799-1834) on Vancouver Island, Canada in 1830. (The Douglas Fir and Phrynosoma douglassi, the Short-horned Lizard, named after him.)
Early Spanish settlers from Mexico called it "yiedra," Spanish for ivy (from the Latin word, "hedra"). Soon "maligna" added to the name, for this was truly an "evil weed." (Toxicodendrons)
In California, the number of working hours lost because of dermatitis caused by poison oak makes it the most hazardous plant in the state.
Poison oak is very resourceful and versatile. Its range extends from sea level to 4000
feet. The soils it prefers are dry, but it can also adjust to living in moist environments. It grows especially well in areas where the ground has been disturbed such as forest trails, city parks, suburban backyards, and roadside embankments (Hauser 2001). Essentially, poison oak is not limited to particular soils or drainage patterns. It does opt for sunnier locations, but the adroit plant can dwell in shady or non-direct sun areas. In vine form, poison oak might kill its support plant by smothering or breaking it due to its opportunistic stem and root system (Harris & Howard 1994). (Toxicodendrons, 1)
However, another source says - In California, it is widespread and grows in a wide range of habitats from sea level to the 5000
-foot elevation, including open woodland, grassy hillsides, coniferous forests, and open chaparral. (Poison Oak, 1)
Although 50% of the population is clinically sensitive to poison oak and poison ivy, about 75 to 85% can potentially develop an allergy if exposed to a sufficiently high concentration of the toxin. The oil in the plants, its called arusiol, and it is an almost invisible -- well, it is invisible to us in the quantities that we would see it in. A very clear, thin oil flows in canals in all parts of the plant. When something breaks the canals such as a broken leaf or even an insect bite, the arusiol comes out, sits on the leaf, and waits for a human to pass by, and when it gets on our skin 85% of us will have an allergic reaction after our first exposure. As with most allergic reactions, you have to have a sensitizing exposure. Then the next exposure, the body decides that this allergen is dangerous and goes after it.
Once a reaction to the toxin has occurred, the body responds with a cell-mediated immunity, which is a delayed hypersensitivity. Those individuals who have developed delayed hypersensitivity are sensitive to the toxin and repeated exposures further increase sensitivity. Conversely, long periods with no exposure will reduce an individual’s susceptibility to the allergen.
• The Biogeography of Toxicodendron diversilobum or Western poison oak: San Francisco State – Department of Geography: by Emily Meriam, 316, Fall 2001 See: http://bss.sfsu.edu/holzman/courses/Fal ... ebsite.htm
• The Toxicodendrons: See: http://ops.tamu.edu/x075bb/caddo/frameidx.html
• Poison Oak, Integrated Pest Management for Home Gardeners and Landscape Professionals: See: http://220.127.116.11/search?q=cache:Orl ... clnk&cd=18