T. rydbergii (western poison ivy) hybridize in the Columbia River Gorge area. Toxicodendron diversilobum is common in various habitats, from mesic riparian zones to xeric chaparral. It thrives in shady and dappled light through full and direct sunlight conditions, at elevations below . The vining form can climb up large shrub and tree trunks into their canopies. Sometimes it kills the support plant by smothering or breaking it. The plant often occurs in chaparral and woodlands, coastal sage scrub, grasslands, and oak woodlands; and Douglas-fir (Pseudotsuga menzesii), hemlock–Sitka spruce, Sequoia sempervirens (coast redwood), Pinus ponderosa (Ponderosa pine), and mixed evergreen forests. Ecology Black-tailed deer, mule deer, California ground squirrels, western gray squirrels, and other indigenous fauna feed on the leaves of the plant. It is rich in phosphorus, calcium, and sulfur. Bird species use the berries for food, and utilize the plant structure for shelter. Neither native animals nor horses, livestock, or dogs demonstrate reactions to urushiol. Due to human allergic reactions, T. diversilobum is usually eradicated from gardens and public landscaped areas. It can be a weed in agricultural fields, orchards, and vineyards. It is usually removed by pruning, herbicides, digging out, or a combination. Toxicity Toxicodendron diversilobum leaves and twigs have a surface oil, urushiol, which causes an allergic reaction. It causes contact dermatitis – an immune-mediated skin inflammation – in four-fifths of humans. Most, if not all, will become sensitized over time with repeated or more concentrated exposure to urushiol. The active components of urushiol have been determined to be unsaturated congeners of 3-heptadecylcatechol with up to three double bonds in an unbranched C17 side chain. In poison ivy, these components are unique in that they contain a -CH2CH2- group in an unbranched alkyl side chain. Exposure Toxicodendron diversilobum skin contact first causes itching; then evolves into dermatitis with inflammation, colorless bumps, severe itching, and blistering. In the dormant deciduous seasons the plant can be difficult to recognize, however contact with leafless branches and twigs also causes allergic reactions. Urushiol volatilizes when burned, and human exposure to T. diversilobum smoke is extremely hazardous, from wildfires, controlled burns, or disposal fires. The smoke can poison people who thought they were immune. Branches used to toast food over campfires can cause reactions internally and externally. Urushiol is also found in the skin of mangos, posing a danger to people sensitized to T. diversilobum when eating the fruit while it