From: The Crime Report
"According to PEER, (Public Employees for Environmental Responsibility) there were 34 incidents involving attacks on US park rangers in 1995. By 2005 the number rose to 477—a 13-fold increase. And in 2012, reported assault incidents rose more than 40% in wildlife refuges and in areas patrolled by the U.S. Park Police, and by more than 12% in national parks. Many assaults were not reported."