Outdoor fires are a special part of camping in Michigan state parks. But if you build a fire at a state park next year, the rules likely will be a little stricter when it comes to what wood you'll be allowed to set ablaze.

Parks officials are working on new proposed firewood restrictions for state parks and DNR-managed public lands for 2018. What this could mean is campers would have to buy their firewood bundles in the park from an approved vendor, or bring in wood that's been certified as heat-treated for emerald ash borer.

This would mean no bringing firewood from home, or stopping by the mom-and-pop vendors whose wood-bundle displays dot the roads leading to many parks.

Michigan Department of Natural Resource officials stress this proposed policy is still being tweaked, and has not been given final approval. While there's been some recent confusion about the rules, Parks and Recreation Chief Ron Olson said he hopes a final version of the new firewood guidelines can be approved by fall - or at the latest, in December.

"The objective is to work on a way to minimize the spread of invasive species," Olson said. "That continues to be a problem."

To prevent the spread of tree-killing diseases, Michigan's environmental and agricultural leaders have long been proponents of the "Buy it where you burn it" mantra when it comes to firewood.

Millions of trees across the state have been killed in recent years by diseases and invasive insects, many times after being carried to a new spot by firewood, the DNR says. Stopping these fatal hitchhikers is at the heart of any new policy, Olson said.

"What we want people to know is that it's a serious problem. Firewood is not the only thing (that spreads disease and insects), but it's proven to be a way that diseases are transmitted."

Why the focus on heat-treating wood from outside areas? It kills insect larvae and other disease that may be on the cut pieces of wood, and spread from one area to another.

"This is one simple way. We realize it's going to take a lot of cooperation from the public."

"A lot of it has to do with educating people," Olson said. "We're not telling people you can't have fires."

Already there's been some backlash. The quality of firewood currently available at some state park campgrounds has people grousing about this proposed change, if people are going to be asked to buy all their firewood at the park. Instead of a nice bundle of logs, campers are offered thin slices of wood at some parks. They burn quickly and require a couple $5 bundles for one evening's campfire.

Olson said the type of firewood for sale at the parks would have to be part of the discussion. If campers are going to depend on in-park firewood, he said the DNR wants them to "have wood they can use to conduct a decent fire."