Fearing that a passerby might tug on the branch and end up stripping the tree of bark, the man made an executive decision to perform an amputation on the spot, twisting the branch over and over until it snapped, while leaving the bark on the trunk intact. To the owner of a nearby restaurant, the emergency procedure looked suspiciously like vandalism. Threats were made to call the police. The arborist remained calm. “It’s O.K.,” he said, and reached for his wallet to produce a laminated badge. “I’m a citizen pruner.