I believe I once read that poison oak is far hardier than most plants in its area, and will take them over if not eradicated or controlled. I used to hike in the Crystal Cove area of Newport Beach, and loved the fact that their high tax rate paid for trail maintance workers to go there every spring and burn or poison the stuff out. (Although I love nature, I admit it made me feel very, very good to see the stuff dead and brown or burnt.) It did not completely eliminate it, but it cut it down 99%. Hopefully, trail volunteers can pick up the slack everywhere now that local governments have less funds for such things.