Since May, more than 1,000 “happy little trees” have popped up across Michigan’s state parks. Planted by hundreds of volunteers who replaced damaged and diseased trees with healthy (and happy) saplings grown by prison inmates, the trees derive their name from artist and television personality Bob Ross’ signature catchphrase.

The so-called Happy Little Trees program is the product of a partnership between the Michigan Department of Natural Resources and Bob Ross Inc. Timed to coincide with the centennial of Michigan’s state parks, the initiative represents a revamped version of what was previously dubbed the “prison grow” program.

As Michelle Coss, volunteer and donor coordinator for the DNR’s Parks and Recreation division, explains to Roadtrippers’ Alexandra Charitan, inmates at three of the state’s correctional facilities are responsible for growing some 1,000 trees every year. These plants—including white cedar, paper birch, sugar maple and other native varieties—are then used in volunteer-driven reforestation projects aimed at replacing trees felled by invasive species.

“We were talking about the prison grow program, and somehow ‘happy little trees’ came up,” Coss tells MLive’s Emily Bingham. “I said, ‘Well, wouldn’t it be cool if we reached out to Bob Ross Inc. and asked if we could use that moniker for the program?' So we did, and they loved it.”

Michigan first launched the prison grow program in 2006, according to DeJanay Booth of the Detroit Free Press. This year, around 30 to 40 prisoners participated in the initiative, nurturing trees later planted in 22 of the state’s 103 parks. Per a press release, sites in the Lower Peninsula (including Fort Custer, Yankee Springs and Silver Lake) received trees in May, while those in the Upper Peninsula (including Tahquamenon Falls, Laughing Whitefish and Muskallonge Lake) received trees in June.

The rebranding has proven popular: After it was announced in April, more than 500 people—perhaps enticed by the promise of a free t-shirt bearing the painter’s likeness—signed up to work as volunteers, CNN’s Lauren M. Johnson writes.

DNR Natural Resources Steward Heidi Frei says that tree damage in state parks stems largely from invasive species spread by human campers. Pests found in firewood originating outside of the region, for example, can infect a single tree that then infects others via its roots, Frei tells WOOD TV8’s Justin Kollar.

The Happy Little Trees initiative circumvents this problem by using seeds from the region in which specific trees will eventually be planted. According to the DNR, this genetic advantage helps saplings better survive a local area’s unique environmental conditions.

For now, “Happy Little Trees Ahead” signs featuring a caricature of the curly-haired artist are on display outside of Port Crescent State Park, Orchard Beach State Park and Yankee Springs Recreation Area. Additional signs will eventually be installed at Ludington State Park, Warren Dunes State Park and Sleeper State Park.

Editor's note, 9/13/19: This piece incorrectly referred to emerald ash borers and oak wilt as plants. The story has been updated.