…As climate change accelerates, the trees in the Eastern forests of the United States are increasingly vulnerable. For many arborists, the challenges facing trees are reshaping and expanding the nature of their work. …To spend time with tree experts is to remove one’s green-tinted glasses and to see Oz as it really is. Many species — including ash, oak, maple, hemlock, elm, and white pine — have their own particular pest or disease threatening them. And there are more pests and diseases on the horizon, including insects like the spotted lanternfly and infections that weakened trees cannot fight off. …Ms. Bezanson of UMass Amherst, who is among those training the next generation of arborists, said she sees rising demand not just regionally but nationwide in the profession’s three principal sectors: commercial, municipal (also called urban forestry), and utility.”