By Gustave Axelson
Age is relative, especially age as defined by humans.
Soon after my wife and I purchased a stucco two-story home built in 1913 in south Minneapolis, I gave a friend from London a lift to the airport and cheerily remarked that I had just bought an "old home." The Brit chortled, amused that I considered a post-Victorian house to be old. She grew up in a home built in the 1700s.
If I had turned our conversation toward trees, I expect I would have encountered the same skew in time dimension. In England, ancient woodlands are those where trees originated in 1600 or earlier. Here in Minnesota, the Department of Natural Resources designates 120 years as the qualifying age for old-growth trees.
To most Americans, the term old-growth forest conjures an image of spectacular grandeur like the giant redwoods of California, like Hyperion — the world's tallest tree at 379 feet. Estimated to be 600 years old, Hyperion is an adolescent among nearby redwoods that are 1,500 years old.
Minnesota's tallest (126 feet) red pine, in Itasca State Park, is one-third of Hyperion's height and half its age. Minnesota might have had more impressive old-growth forests if its tallest and oldest and straightest trees hadn't been plundered 100 to 150 years ago by timber barons. Prior to European settlement, about half of Minnesota's forests were old growth. Today that proportion is less than 4 percent. And most of those old trees among Minnesota's 44,000 acres of designated old-growth forests aren't even 100 feet tall, mere footstools for Hyperion.
But walk with a forest ecologist into some of these relatively ancient woodlands of pines, birches, oaks, and maples, and you'll soon learn that a search focused myopically on big, old trees forsakes the beauty of the workings of an old forest.
Before the big cut of the 19th and early 20th centuries, pines -- red (Pinus resinosa) and white (P. strobus) — were prominent throughout Minnesota's northern forests, covering 3.5 million acres. According to a 2004 statewide forest inventory, pines in the 21st century cover a little more than a half million acres, fragments of a once great pine kingdom.
On a boat crossing Lake Vermilion toward Pine Island, I see a vision that might have resembled that kingdom. "There's the super canopy of pines above the birches," DNR ecologist Steve Wilson yells over the buzzing boat motor. Wilson's finger points to stately splayed, massive boughs of large pines towering above the island forest. Most of Pine Island is owned by the DNR as Kabetogama State Forest and by the U.S. Forest Service as parcels of Superior National Forest. Wilson has invited his friend and USFS counterpart, botanist Jack Greenlee, to join our excursion.
The boat lands, and our party bushwhacks into dense balsam woods. About 100 yards into the bush, we stop as the floor vegetation turns sparse. Dried red needles cover the ground. I look up — way up — and see pines. These pines are about 90 feet tall, estimated to be between 185 and 193 years old. Oddly, my eyes round a curve as they run the course of these trees from base to crown. At about 50 feet high, all of the tree trunks gently veer — some left, some right.
I query Wilson about these curvy pines, and he's puzzled. "Maybe there were porcupines on this island years ago?" he shrugs. "Maybe an insect infestation?"
A sly smile cracks his square jaw and gray-stubbled face: "Maybe aliens?"
Wilson is tall and lean like these pines, with the trim build of a man who mostly derives his fat and protein from nuts and venison. He last walked here in 1991, when he surveyed this forest to get it protected under the DNR policy of reserving the "highest quality remaining natural old-growth forest communities."
My neck remains craned — gazing up into the pines — until I notice that Wilson and Greenlee are looking down and around. I ask Greenlee what strikes him about this place as he examines the carpet of kelly-green lichens that cover a log.
"Oh, it's the coarse woody debris," he chirps with a scientist's enthusiasm for the obscure. "I mostly travel in managed pine stands in my job, so I never get to see all these snags and deadfall. It's beautiful."
I ask the same of Wilson; and he says, "Patchiness." To demonstrate, he leads me into a sun-bathed opening where, he says, balsam firs probably grew old, died, and were blown down. Now pine seedlings have sprouted in their stead. Next, Wilson leads me into a stand of tall pines where cedars grow in the understory. "Patch dynamics are a key old-growth characteristic," he says. And patchiness begets biodiversity. Wilson suddenly stops talking to identify the flutelike call of a Swainson's thrush, a species that sticks closely to conifer habitats. Within moments, Wilson rattles off several calling warblers: pine, blackburnian, northern parula, and black-throated green. Then he chuckles. "When I was in college, I once heard a professor declare that 'Old-growth forests are a biological desert!'"
Another hour of hiking takes us to a piece of old-growth artwork, arranged by serendipity. Two mighty big trees — a white spruce and a red pine — have fallen toward each other at 60-degree angles. Their roots evidently lost their footing in the thin soil here. Both are supported by a stalwart red pine in the middle, where the two partly fallen trees caught on branches about 70 feet high. The sight looks like the framework for a giant teepee, or two drunken buddies leaning on a solidly sober friend. Astonishingly, all three trees still sport green foliage. Wilson estimates the spruce to be 150 years old, and the pines about 190. "A fluke of nature prolongs their longevity," he notes.
We break for lunch near a downed, big old pine that wasn't lucky enough to find a friend's shoulder (I count off 55 footsteps in walking the length of the massive log). "You see weird things in old growth, because there's been so much more time for the forest to develop character," Wilson says. "So many more opportunities for things to happen that would make a tree twisty or contorted."
"I know exactly what I'll see in a tree plantation," Greenlee adds. "Come out to an old-growth forest like this, and you never know what you're going to find."
While Wilson and Greenlee finish up their lunches, I wander over to a couple of 90-foot pines, a red and a white. The characteristics of pine bark seem exaggerated in old age: The red pine's bark scales are larger than my hands, and the white pine's bark furrows are so deep I can stick my entire finger into them. I lean my back against the white pine and look straight up: About 70 feet high, the trunk swerves.
There are few thrills like the sensation of stepping off trail and into the bush, off the regimented and into the unknown. I take a deep breath, close my eyes so they don't get poked by branches, and walk through a thicket of mountain maples. I am leaving the Matt Willis Trail at the southern end of George H. Crosby–Manitou State Park, following DNR ecologist Chel Anderson into the backcountry where old-growth yellow birches grow in moist soils among cedars and maples.
Yellow birches range from Canada's Maritime Provinces west to Minnesota. A cousin of the beloved paper birch of the north woods, yellow birches similarly have finely toothed, oblong leaves. And though both birch species have peeling bark, that of the yellow birch is yellowish to bronze, hence its name.
I'm on the lookout for that characteristic bronzed bark, so when I walk up to my first old-growth yellow birch, I don't recognize it.
"That yellow birch is between 300 and 400 years old," Anderson says as she points to a tree trunk thicker than I can wrap my arms around. The bark is furrowed and gray; I thought it was a pine just from looking at the base. But that's like trying to determine what a person looks like by staring at the feet. As my eyes climb the tree, I see peeling, bronze bark about 30 feet up. At the treetop, tiny silhouettes of birch leaves dance in the breeze.
A closer look at the bark at my height reveals that the grayish features are actually shield lichens. "Those lichens themselves could be hundreds of years old," Anderson informs. Old-growth lichens growing on an old-growth tree.
Now that I know what I'm looking for, I see the robust trunks of several old yellow birches, spaced about 10 yards apart. One has a giant burl the size of a basketball. Another grows slanted at 45 degrees. Anderson walks over and knowingly rubs its bark. "Just imagine that when this yellow birch was a sapling, hundreds of years ago, a tree probably fell right on top of it and forced it to grow at this angle. Now that dead tree is gone, completely deteriorated. And this tree has spent its whole life growing in an odd way, just because of that one event."
Downed trees, which abound in old-growth forests that haven't been cleared by humans, are integral to yellow birches. A bit farther into this old grove, Anderson finds a line of yellow birch saplings sprouted along a cedar log-bonsai — size birches with smart orange stems and sprightly green, serrated leaves. Downed cedars and their rot-resistant wood provide a stable spot for saplings to grow elevated from the spongy duff of maple leaf litter. I look back at the big, old yellow birches I couldn't identify a few minutes ago, and now I see the secret to their formation: lines. Bunches of three and four birches grow in rows along what hundreds of years ago must have been downed cedars.
But I don't see any middle-aged yellow birches. That's because, in the past century, burgeoning deer herds have used the downed cedars as buffet lines. Deer come along and snap up the handsomely presented yellow birch saplings before the trees reach adulthood.
Today yellow birch stands are perhaps the rarest of the state's old-growth remnants. According to Lee Frelich, director of the Center for Hardwood Ecology at the University of Minnesota, only about two-tenths of 1 percent of yellow birches are left from presettlement times, due to intensive logging after World War II when yellow birch's finely grained qualities for furniture were valued. Now the timber market in Minnesota has shifted largely to pulpwood, so an incentive hasn't existed to replant yellow birches.
Ironically, a logging experiment in a nearby county forest might represent the best hope for yellow birches. There The Nature Conservancy is overseeing selective harvesting in a sugar maple forest for pulp. The project, known as the Manitou Forest Collaborative, is harvesting in a spatial pattern that mimics the gaps in the old-growth forest of maples, cedars, and birches within Crosby–Manitou State Park. The question is, can yellow birches regenerate given enough space — despite deer?
Lots of questions still need to be answered about the yellow birch white cedar forest community, which Anderson says was only recognized by foresters within the past 10 years.
"So little is known about these communities and the relationships within them," Anderson says, "which means so much is at risk of being lost if they disappear."
We are back on the Matt Willis Trail, finishing up our hike, when Anderson and I finally find an adolescent yellow birch, a properly copper-barked birch that hasn't been grayed by lichens yet. Anderson pauses to run her fingers gently across the horizontal striations of its bark.
"Just look at how it's so golden when the sun shines on it. It's so metallic," Anderson says admiringly. Then she looks down at the rocks that form a stony path along the trail, and a querying look forms on her face. "I often see yellow birches growing in these cobbly areas. I presume they are taking advantage of the lack of maple leaf litter, but there's likely more to it than meets the eye. Lots of questions come to mind."
More discoveries wait to be made, perhaps, in an old-growth forest type that was only recently discovered itself.
On a wet autumn day, Chel Anderson and I don rain jackets and walk into Tettegouche State Park from the back entrance along Lax Lake Road. Today, the DNR ecologist will guide me to a stand of red oaks more than 150 years old. The two south-facing ridges where they grow in Tettegouche — sunny spots with shallow, dry soils, which Anderson calls xeric — are the northernmost stands of red oak in Minnesota.
Shallow soil doesn't make for big trees. Many oaks on this ridge are the diameter of signposts. But their age shows in the rough, craggy bark, stitched with lichens. Their long, crooked boughs are flush with flashy red leaves and laden with acorns.
Some of these oaks have piles of denuded branches at their base. Anderson tells me that black bear sows have climbed into the trees, snapped off limbs, and dropped them — along with their acorns — to cubs waiting below. Ely bear biologist Lynn Rogers first documented this phenomenon of a bear teaching her young how to harvest acorns here in 1972. His research also showed that the acorn-eating bears were healthier, fatter, and more fecund than other bears in his study. And cubs born of an acorn-harvesting sow returned to this oak stand on their own as adults, some bringing their own cubs in tow. Perhaps that's another reason why these old red oaks look a bit stunted-annual pruning by bears. Anderson stands by an old oak and studies a wound in the bark, now healed over and covered by lichens. Perhaps, she says, it was caused 75 years ago by the great-grandparents of bears that migrate here in fall today, a family tradition among North Shore bear clans.
Two decades ago there was another nearby old-growth stand of red oaks for bears to forage among, but it was logged for firewood. That spurred Rogers to enlist The Nature Conservancy and the Parks & Trails Council of Minnesota in getting this ridge of old-growth oaks added to Tettegouche State Park in 1993. Today these oaks — which may take 50 years to produce their first good acorn crop but then yield acorn bounties for another 200 years — are primed to live out the rest of their natural lives filling the bellies of bears.
According to Anderson, research findings, such as the migration of bears to isolated oak forests to feast on acorns, are perhaps the most important reason to protect old growth:
"What's important isn't that we wall off 1 percent of our forests and declare them old growth and off limits to management. What's important is that we observe and learn how old-growth ecosystems function and what relationships they support. For bears. For trees. For understory plants, soil invertebrates, and people. And that we use that knowledge across the landscape on the other 99 percent of lands we manage to sustain the whole community of life."
I stoop to pick up an oak leaf from the ground near the end of our walk, and I'm struck by the leaf's luminance. The cold autumn drizzle has matured into a drenching. Water drips from the tips of bare oak branches, and the end of my nose, and inside my rain jacket. The overcast sky yields no sunlight, yet the leaf, wet and shiny, seemingly glows from within-a ruby shining in its own right.
Walking in old-growth forests can be open and clunky. Open in that old-growth canopies create shaded understories inhospitable to brush. Clunky in that the forest floor is unevenly strewn with logs and branches — what ecologists affectionately call coarse woody debris.
So as I step into Spring Beauty Northern Hardwoods Scientific and Natural Area near Hovland, I'm never quite sure just how far my foot will sink into the lush bed of maple leaf litter here. Will it firmly rest on a solid log? Will it depress into mushy rot? Will it plunge into a pot of leaves and only leaves? Only each footstep knows.
In this jostling, awkward manner, I am following Chel Anderson, again my DNR old-growth ecologist guide, into a grove of sugar maples where some trees are 200 to 300 years old. A sugar maple forest has stood here for 2,000 to 3,000 years, maybe longer. Sugar maples were more prominent in this Arrowhead region before the relatively recent cooling climate of the past three millennia. Over that time, conifers established their dominance in the north woods and sugar maples receded to ridgetops. Only up here — perched at 1,600-feet elevation, three miles inland from Lake Superior — have the suitable conditions of a warmer springs–snowier winters microclimate allowed sugar maples to stay.
Anderson pauses at one of these maple old-timers — a stout specimen with a trunk as wide as a barrel and scaly dark-brown bark that's quite unlike the smooth gray bark of younger sugar maples. She wagers its age is about 130 years. Deep frost cracks are evident, formed when water in the inner bark and wood rapidly froze and expanded on cold spring nights. Frost cracks are a condition of Acer saccharum growing at 47 degrees north latitude and the reason why these trees were unmerchantable as lumber.
But they were productive for maple syruping, as attested to by the sugar bush artifacts in the leaf litter nearby. Locals say that the man who tapped these trees, a fellow named Bill Deater, passed away about 25 years ago. All that remains of his sugar shack now are a rusty metal pail, a few nails, and tar paper from the roof, ruins being swallowed by the duff at the glacial pace of a few centimeters annually by each autumn's deposit of fallen leaves.
The duff, or leaf litter, here is remarkably deep. I kneel down and stick my finger into cool, damp, spongy detritus, digging for several inches and never reaching soil. It's the perfect bed for cultivating maple seedlings. The occasional cedar or birch grows on islands of mineral soil exposed by the roots of windblown trees, a feature that Anderson calls tip-up mounds. But by and large, these woods are in a stable and self-perpetuating state, solidly dominated by maples and unwilling to succeed to a different forest type. No other tree's seeds can survive the suffocating duff here.
And few other trees could grow here beneath the coalesced canopy of palm-sized maple leaves that cast this forest in one continuous shadow.
Occasionally, flecks of sunlight peek through the canopy and dapple the forest floor. That's all a maple sapling needs, Anderson tells me. She picks a large leaf off an ankle-high maple and shows me its delicate thinness. "It's highly efficient at converting sporadic bursts of light into growing power," she says. Then she wraps her hand around a frail tree that's about my height and the diameter of my thumb. Its leaves are thicker and darker and smaller. "This tree's probably about 40 years old," she says. "It didn't get very far on the super solar panel leaves of its youth."
As we walk among maples of all sizes, Anderson explains that about 20 percent of seedlings die in their first year. And ankle-high saplings that exhibit genetic superiority will pass up most of the 10-foot-tall trees we see today. "Due to natural selection, generation after generation, only the strongest trees make it to the canopy," she says, patting another of the stout old maples as she walks by it.
Genetic superiority in old growth, she says, gives us a hedge against the drastic changes in northern forests over the next 100 years predicted by Lee Frelich, director of the Center for Hardwood Ecology at the University of Minnesota. Frelich foresees a 21st century in which global warming ends the coolness of recent millennia, and boreal tree species such as fir, spruce, and birch disappear. If global warming can be stemmed to keep Minnesota suitable for some kind of forest, Frelich says a network of old-growth reserves will provide precious gene pools of alpha trees that may be able to weather the coming climatic storm.
For such a dire prediction, it's a good thing these old maples are up on this ridgetop. Ready to reforest North Shore woodlands in the wake of retreating conifers. Poised to come down from their mountain.