MANKATO — The deer will eat well this winter. Thanks to a bountiful mass-seeding of oak trees, acorns lay thick on the ground in south-central Minnesota, as they do around the country.

This phenomenon is called “masting,” and it happens every few years, said Eli Sagor, director of the University of Minnesota’s Sustainable Forests Education Cooperative. We took seven masting questions to Sagor and other experts to explain the how it works and what effects it might have.

What causes a masting to occur in a specific year?

It doesn’t appear to be related to good growing conditions in the spring and summer leading up to the masting, Sagor said.

“That’s a little bit baffling, isn’t it?” he says. You’d think that, as with farmers’ crops, good weather would mean a bumper crop.

Instead, masting years do tend to be correlated with the length of time since the last masting. If it’s been three or four years since the last masting, there’s a higher likelihood that one will come soon.

That makes sense, Sagor said, considering each oak tree expends a tremendous amount of energy to produce thousands of acorns at once. Masting is the tree equivalent of running a marathon, he said, a task they may not be able to do two years in a row.

Why do mastings occur at all?

Just as sea turtles hatch all at once and mayflies swarm, oak trees mast to overwhelm their predators.

When acorns drop a few at a time, forest mammals like deer and raccoons can keep up. But if there are more nuts than animals can eat, at least some will survive.

Why are there so many oak trees in Mankato?

The bicolor oak in particular performs well in city boulevards and parks, said Ashley Steevens, Mankato parks supt. and former city forester. It’s tolerant of salt and other urban pollutants, and its narrower canopy gives more clearance between roofs and power lines, reducing trimming requests.

Can I start an oak tree in my yard?

Sure, but it’s not as simple as it looks. As Sagor was walking on the University of Minnesota campus earlier this year, he stuffed a few dozen bur and white oak acorns into his pocket.

He buried them in his fenced garden, but when he checked back a few weeks later, they were gone, perhaps looted by a squirrel. He’d buried the seeds on a lark; if he’d been serious Sagor would have caged them, both on the side and over the top.

He also notes that some oak seedlings will germinate in the fall, but others, especially red oaks, must go through a spate of cold weather first. This helps ensure the seeds will not sprout in midwinter.

One potential advantage of oaks is that they can grow in the shade.

Might animals benefit from a masting?

A fall of plenty may lead to a fecund spring for rodents, deer, birds, beers, rabbits, deer and other animals.

“It’s an important food source for deer, rabbits and rodents, so we can expect a bump in population though I can’t say that for sure is going to happen,” Steevens said.

Are trails being cleared of acorns?

Yes, but keeping them clear can feel like a Sisyphean task, as they seem to quickly revert to their natural cluttered state.

“We do try to blow off the trail weekly,” Dennis Reindl, manager of the Sakatah State Park, said of the trail of the same name. “Some of these years as soon as you get through with the blower an hour later it’s like you were never there.”

Could masting lead to more Lyme disease?

OK, this question may not have occurred to us, either, but Sagor noted mice eat acorns and are an important carrier of the tick that spreads Lyme disease and similar illnesses.

The connection between acorns and Lyme disease is a reminder of the interdepencies in nature, he says. And the fact that people are talking about masting is a pleasure to him.

“I think it’s great that people are noticing that nature is happening around us, even in increasingly urban areas.”

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