In the first whodunit of its kind in Dakota County, authorities are handling a case that involves murdered trees.

The Dakota County Sheriff's Office launched an investigation Wednesday to find vandals who have stripped rings of bark from seven trees in Lebanon Hills Regional Park. This type of damage, also known as girdling, causes trees to starve and die. Costs to cut down and replace the trees will total about $5,000, said Steve Sullivan, Dakota County parks director.

Because the costs exceed $1,000, the crime will likely be charged as a felony, said chief sheriff's deputy Joe Leko.

Professionals sometimes girdle trees to help clear forests, since trees almost always die from it.

"This is an extremely unique situation, one that I haven't heard of occurring within other public parks," Sullivan said.

Park officials first learned of the vandalism through the Minnesota Off-Road Cyclists, Sullivan said. The group also posted a picture of the incident to Facebook, drawing emotional responses.

"Whoever did this knew what they were doing," said one commenter, who identified himself as an arborist. "The only possibility of repair would have had to take place within the first 24 hours and the process is difficult on mature trees."

"Someone who actually knows about trees is systematically setting out to kill them," another person wrote. "In a park. I just can't get my mind around this one. It is literally a serial tree killer."

The 2,000-acre park spans Eagan, Apple Valley and Rosemount. So far, officials have found girdled trees just in the Eagan area, Sullivan said.

The girdling comes as Dakota County invests $1.3 million in the park, which includes planting 1,500 trees and removing buckthorn, Sullivan said.

"We've had over 2,000 hours of volunteer labor to do natural resource enhancements," Sullivan said. "So when someone destroys natural resources, it's contrary to the commitment that both the public and Dakota County is making."

Jackie Renzetti is a University of Minnesota student on assignment for the Star Tribune.