Last winter, forester John Goodfellow and a crew of volunteers counted the trees along the streets of Marine on St. Croix.

All 925 of them.

They froze their fingers recording the species and size in a digital database.

The volunteers were assessing the value of the “urban forest” and helping prepare for its future. The city is using the information to plan planting, maintenance, and is seeking “Tree City” certification from the Arbor Day Foundation. Goodfellow is a St. Croix Master Watershed Steward and the Urban Forestry Plan was his Capstone Project for the program.

Most of the trees were spruce or ash (there were at least 37 species total), but one sprawling black willow (Salix nigra) caught Goodfellow’s eye.

The tree wasn’t just big, it was huge.

After measuring the circumference of its trunk, its height, and the spread of its canopy, he suspected it was a record-breaking specimen of black willow.

Twenty-six feet around at the base, the giant water-loving tree was growing in front of a house about 150 yards from the St. Croix River. A trickle of spring water flows through the ditch, over its roots. (Because it is located on private property, the exact location will not be disclosed.)

“It is filled with birdsong in the springtime and orioles use it to build dramatically high, swinging nests,” says tree neighbor Ann Kirn.

On a frigid January day, Goodfellow returned to the tree to measure it again. It was leafless but still shaggy, sprouting twigs and branches every which way. And it was still really big.

He submitted an application to have it declared the largest black willow in the state. In June, state forester Jennifer Teegarden took measurements for the Department of Natural Resources and confirmed it: The tree is the largest known example of the species in the state. It has now been added to Minnesota’s official Big Tree Registry.

To make the list, trees are awarded points based on a formula: Circumference in inches + height in feet + 25 percent of the crown spread in feet. The Marine willow has a circumference of 315 inches (26′ 4″), a height of 91 feet, and an average crown spread of 75 feet — for a total of 425 points.

That also makes it the third-largest tree of any species in Minnesota, 10 points smaller than the biggest silver maple and 103 points smaller than the biggest cottonwood.

Next year, the tree could be declared the national champion. It appears to be significantly larger than the current record-holder in New Hampshire: 113 inches (9′ 5″) greater in circumference, 16 feet taller, and 2 feet smaller in average crown spread than the current national champion.

But the deadline for 2017 entries has passed. The willow be crowned next year only if no larger specimen is found in the meantime.

“Like many big trees, it is showing signs of aging,” says Teegarden. The species grows fast and dies relatively young — the oldest black willow ever found in Minnesota was only 85 years old.

That fact highlights another valuable insight from Marine’s tree survey: the city’s tree population is mostly big and old, and the prevalence of ash means it is susceptible to the Emerald Ash Borer, a non-native insect which is expected to kill almost all ash trees in the state in the years ahead.

Plans are underway to start planting more trees to prepare the forest for the future.

Thankfully, some Minnesota arborists are excited about the big willow. S&S Tree Service of South St. Paul is donating pruning and other maintenance for the black willow (its parent company, Davey Tree Survey, is a major sponsor of the National Big Tree program).

“This is kind of like the sate record walleye!” Goodfellow says.

The wood from Black willows is known to be light and doesn’t splinter easily — that’s why it was once used to make prosthetic limbs. The Ojibwe people and other Native Americans use willow (oziisigobiminzh) to make baskets. The tree’s bark and leaves also contain salicin, the basis for aspirin, and it’s historically been used to treat rheumatism and other pains.

Black willow is an important tree species along the St. Croix River and the entire Mississippi River. It only grows in wet soils, and loves floodplains. Its dense root systems help hold riverbanks in place.

Such trees have priceless benefits to St. Croix River communities. In Marine on St. Croix alone, the tree survey found that the forest provides almost $50,000 in stormwater mitigation, slowing runoff and reducing erosion.