What’s an example of a harmful tree?

In our case, buckthorn and honeysuckle. They’re not native. They send out poison to the good trees and kill them. They’re hard to get rid of. The consultant knows how to safely remove and prevent them re-growing.

In much of the Southwest USA, invasive tamarisk, Russian olive, Siberian elm have largely displaced native cottonwood and willow. They are all very difficult to remove.