This ancient tree is one of the oldest in Minnesota.

The warming climate might kill it.

Boundary Waters visitors seek out the Legacy Tree, a northern white cedar that's a bridge to Minnesota's past.

0The 400-pound sled lurches over a downed birch tree, six dogs pulling at full speed despite the guide's "whoa!" — and the sled careens onto its side.

In any other February, a blanket of snow would allow teams from Wintergreen Dogsled Lodge to glide through this portage, which leads to Basswood Lake on the U.S.-Canada border. This winter, however, has left much of the Boundary Waters Canoe Area Wilderness snowless, so instead, two guides and six visitors face 5 miles of lifting their sleds over logs and trudging through mud.

The group braves the unseasonal conditions hoping to see the Legacy Tree, a northern white cedar said to be over a thousand years old.

Deep in border lake country, the tree has gained a mythical profile, prompting BWCAW visitors to seek it out today, just as people have for centuries. The tree may have germinated long before the voyageurs, before the Ojibwe, before even the Dakota. It is a bridge to Minnesota's past, but it may not survive Minnesota's future climate.

"All these old trees will probably die soon," said Lee Frelich, director of the University of Minnesota Center for Forest Ecology, who has studied the Boundary Waters' ancient cedars.

These trees have survived in refuges such as swamps, islands and rocky outcrops that protect them from fires. But Frelich said these areas don't protect them from drought and blistering heat, a climate change-driven combo that is deadly for conifers.

This winter offers a preview of a future Minnesota's warmer climate — what Wintergreen founder and guide Paul Schurke calls "a very despairing new normal."

Schurke, 69, knows what winter should feel like — he's been to the North Pole seven times. He laments that he never felt cold this season, despite spending much of it sleeping outside on trips he runs through his Ely-based outfitter.

Schurke first came to the Legacy Tree as a child; visiting it has become a ritual.

"We're in such dark existential times," he said. "It gives us hope because it's seen its own share of existential threats."

Old trees conjure images of a towering cathedral of the forest, but this shy cedar remains out of sight, though it's just offshore. Its roots, both exposed and reaching deep underground, anchor the tree into bedrock. Its trunk is nearly 15 feet in circumference at its base. It corkscrews upward, frozen in perpetual motion.

The tree has withstood dozens of windstorms, endured drought and dodged fires that burn a swath of the Boundary Waters roughly every century. It even escaped the Swallow and Hopkins lumber mill, which leveled the surrounding forest.

The tree's true age is a mystery. In their 1984 book "Lob Trees in the Wilderness," the late BWCAW researchers Clifford and Isabel Ahlgren write about boring a core from the trunk and finding the inside of the tree rotted. They counted 400 rings and extrapolated the remaining number required to fill the inner core.

That extrapolation estimated the tree to be "well over eleven hundred years old" — which would make the cedar the oldest known tree in Minnesota.

That kind of guesswork doesn't hold water with modern dendrochronologists — scientists who study tree rings. To more than double the rings you have is "a wild extrapolation," according to University of Minnesota dendrochronologist Dan Griffin, who has documented some of the oldest trees in eastern North America.

Griffin said modern tree ring research relies on rigorous methods to precisely link a ring to the year the tree laid it down.

That kind of rigor can't be applied in this case.

"The oldest-looking trees aren't willing to give that info up. They tend to be hollow," he said. "Their stories tend to be lost to time."

The Legacy Tree's status as Minnesota's oldest may be unknowable, but scientists believe many cedars in the Boundary Waters could be a thousand years old.

The Legacy Tree's grove in a calm bay was once near a marked campsite. Like many BWCAW campsites, it's what Superior National Forest archaeologist Lee Johnson calls a "persistent place," meaning people have been camping here for centuries.

"It would've seen different people coming through there. The Cree, the Dakota, and then the Ojibwe, and who knows before that," said Heart Warrior Chosa, a Bois Forte band member who lived on Basswood Lake inside the Boundary Waters off and on until 1991.

Chosa, 78, would pass the tree occasionally on fishing trips and often brought offerings of tobacco as a sign of respect to an elder. Nookomis giizhik, or grandmother cedar, was a woman who so loved her people that she died so she could be reborn as medicine, according to Ojibwe oral tradition.

"Cedar is purifying. It's the medicine tree," Chosa said.

Cedar is one of four herbs considered sacred to the Ojibwe and other Indigenous peoples, along with tobacco, sweetgrass and sage. Its leaves can be brewed into an anti-inflammatory tea, and its rot-resistant wood was used to frame birchbark canoes.

"These trees, especially the cedar trees, would have seen a lot and have memory of a lot of things that went by, back to a time of peace," Chosa said. "Through the years, who knows what it saw or felt."

Old trees are genetically resilient to all the challenges they have faced in their lifetime, potentially giving them an advantage, Frelich said. As a result, seeds from so-called legacy trees are valuable — the "knowledge in their genes" could be key to their survival. However, that knowledge applies to an older climate, one that is vanishing fast.

"We're getting out of the range of anything they've experienced in their thousand years of life," Frelich said.

Droughts and extreme heat diminish a tree's ability to defend itself against predators. Shorter winters allow pests to hatch earlier and hit harder. The arborvitae leafminer, a native moth, damaged 4,000 acres of northern white cedar in a 2018 outbreak, according to the Minnesota Department of Natural Resources.

While all old trees eventually die, the cumulative toll of rising temperatures could take them all out in a short span, Frelich said.

"If the climate only goes up one degree [Celsius], they'll be fine," he said. "If it goes above that, the climate could be warmer than anything the species has experienced in the last few million years."

For Chosa, it's clear what it would mean to rapidly lose the legacy trees: "People lose their heritage, lose their memories."

Those who visit the tree should do so humbly, said Andy Hill, a retired guide who lives in Ely. He hopes visitors will keep its location obscure so that it's not overrun.

Hill explored the Boundary Waters for 20 years before an older fisherman brought him to the tree. By the time he camped out with it on New Year's Eve in 1999, the Legacy Tree was an "old friend." He welcomed the new millennium with an organism that may have seen the previous one.

Twenty-four years later, during the mid-February trip, Schurke's 10-year-old lead dog, Whoopsie, curls up in a little hollow at the tree's base. Schurke places a wad of tobacco in a groove in the gnarled bark, his way of showing respect and reverence. He meditates on the immense changes the great cedar has endured — and the resilience required to survive them.

"We can identify with this tree," said Schurke. "But we've only lived through one millennial [change]."

Sources and methodology

Historical wildfire perimeters are derived from the work of U.S. Forest Service researcher Miron Heinselman, who estimated the geographic extent of past fires based on burn scars in red pine tree ring cores, dating and cross-referencing hundreds of tree cores taken across the Boundary Waters over many years.

The tree core sample was collected by University of Minnesota professor of geography Kurt Kipfmueller from a northern white cedar on Sea Gull Lake in 2005. U Ph.D. student Naomi Schulberg refinished the core and verified its age.

The Ojibwe name for Basswood Lake is derived from "Lac La Croix First Nation: Quetico's Traditional Lake Names," by Kalvin and Margaret Ottertail. The lake is referred to as Baate Miinaang Zaaga'igan in other communities. Other Ojibwe words use spellings from the Ojibwe People's Dictionary.

The Boundary Waters Canoe Area became a federally recognized wilderness with the passage of the 1964 Wilderness Act. The 1978 Boundary Waters Canoe Area Wilderness Act banned logging, mining and snowmobile use, limited motorboat use, and added "Wilderness" to the name.

Tree illustration by Mark Boswell • Star Tribune