Zimmerman, 74, was appointed to fill out an unexpired term in 1978 and served until this year, said Nate Bacon, a local photographer and tree commission chairman.
"It took about five months to find a replacement for Harold. He will really be missed. His experience and knowledge of this community is irreplaceable. It's good that he's going to get some recognition. Harold gave nearly 20 years of his life making Greencastle a greener place," Bacon said.
Zimmerman said he resigned after 18 1/2 years because he'd been on the commission long enough. "I served my time and I've learned a lot, but now it's someone else's turn. I enjoyed serving the town and the people." he said.
Zimmerman will be honored for his years of service Saturday when a sugar maple is planted in his name at a 10 a.m. ceremony at the Jerome R. King Playground on North Carlisle Street.
The three-member Shadetree Commission has a $3,000 annual budget to spend on new trees, replacing old or diseased trees and trimming and spraying existing ones, Bacon said. About 18 new trees will be planted this year, he said.
The commission members are Bacon, Karen Hudson and Karen Johnson, Zimmerman's replacement. They are responsible for all trees, shrubs and hedges that grow within 15 feet of a street curb, including those on private property. Owners need permits to plant, remove or trim trees, shrubs and hedges growing within the 15-foot boundary, Bacon said.
The commission can order trees or shrubs removed if they become a danger or if they block visibility to traffic, Bacon said. The members also work with the power company on trees that endanger power lines.
Zimmerman's knowledge of the community often came into play at commission meetings, Bacon said. When reviewing a permit application, Zimmerman frequently knew of the property in question, he said.
Zimmerman started the funeral business at 45 S. Carlisle St. that bears his name in 1948 after military service in World War II.