Actually they tried the normal way, where they didn’t shoot and asked the poachers to surrender / tried to arrest them. But the rangers would get shot and the animals would continue to get poached.
Seeing this as a problem, a new executive order / law was passed allowing shoot at sight orders at national parks / protected zones.
Poaching has reduced, the number of rangers getting shot has reduced. The number of poachers getting shot has reduced (they don’t wanna fuck around anymore).