On a recent hike to Wildcat Peak in Tilden Park, I was enjoying the sweeping vista of the SF Bay, grateful to be living in such a wonderful place, when I absently strayed from the center of the trail. Awaiting me was the ever dreaded three oily leaves of poison oak that often line the sides of the path and in some places creating an obstacle course as its branches reached across the trail. A brief panic erupted after this encounter, as I anticipated an irritating rash emerging in 2-3 days on my leg.
Fortunately, I was spared the discomfort this time around, but I am sure I will have many more opportunities this summer to come in contact with poison oak. Frequently hikers and explorers of the Bay’s parks might have noticed the exploding poison oak this season, and the plant’s growth is part of a larger story of changing habitats, drought, and climate change.
Pacific poison oak, Toxicodendron diversilobum, is native to most regions in California and thrives in our oak woodlands, and nearly every other habitat in the state under an elevation of 5,000 feet. A deciduous plant, it loses its leaves in the winter, and has green spring leaves that gradually transform into reds, oranges, and yellows by the autumn months. While the leaves can arguably be described as beautiful, the painful rash from the toxic oily urushiol on the leaves and stems is what the plant is most known for. Sometimes, before the leaves have dried out or been covered by dust, the oil is extremely shiny and nearly dripping from the leaves.
Poison oak is easy to hate, especially after days (or weeks!) of an irritating rash, but its resiliency is to be admired, especially with impacts of climate change. The plant is remarkable adaptable, proving to be extremely resistant to a variety of environmental stressors, as we recently witnessed during California’s five year drought and is capably of thriving in many habitats. Usually, it stays below an elevation of 5,000 feet, but with the changing climate, observers have found the pesky plant growing at higher elevation levels as the climate becomes more conducive to poison oak growth.
Poison oak is a component of the changing landscapes of California. While it is native to the region, its adaptibility allows for the plant to continue spending and finding new habitat, unlike many plants that find their narrow preferred habitat shrinking. While this plant is clearly not a favorite of many, nor is it one that most people would want in a garden, it can be admired from afar.