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The Lilliputian forest

Harsh conditions make survival a constant challenge in a Minnesota peatland

Marshall Helmberger
Posted 4/4/19

Our early spring sun, combined with a lack of any appreciable new snow, has been steadily eating away at our snowpack. So, I took advantage of last weekend’s chilly temperatures to make what I …

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The Lilliputian forest

Harsh conditions make survival a constant challenge in a Minnesota peatland

Posted

Our early spring sun, combined with a lack of any appreciable new snow, has been steadily eating away at our snowpack. So, I took advantage of last weekend’s chilly temperatures to make what I expect will be my last fat tire bike foray of the season into the Lost Lake Swamp.

As I’ve written before, I most often make my treks into this sprawling peatland in search of big trees— the kind long forgotten on some of the remote upland islands that are most easily accessed during our season of “The Crust.”

But on my latest visit, I was looking for quite the opposite. The swamp might offer ideal growing conditions for the bog heaths, like leatherleaf and bog rosemary, but surviving the challenging conditions there is almost impossible for most other plants, particularly most of our native trees. The only exceptions are the black spruce and tamarack, which tend to dominate what passes for forest cover in most of our area peatlands.

The black spruce does best in sites dominated by cold, wet, acidic soils, which are commonplace from northern Minnesota right up the tree line in northern Canada. These are the types of sites where black spruce will grow in dense stands to a harvestable size in our region. And there are many such sites along the edges of the Lost Lake Swamp. But across the vast majority of this sprawling peatland, the trees are noticeably stunted, comprising natural bonsai forests that can stretch for miles. In fact, Minnesota has something on the order of a million acres of stunted black spruce.

While trees are common here, the landscape is really dominated by the bog heaths, sedges, and sphagnum moss that cover the “ground.” In another few weeks, these wet places, which can seem prairie-like in their openness, will be home to singing savannah sparrows, sandhill cranes, and sharptail grouse.

In such places, individual hummocks of moss can seem to be home to their own Lilliputian forest of black spruce, with an occasional tamarack thrown in for variety. The tiny black spruce may appear to be individual trees, but often they are clones which sprouted from lower branches of the parent tree after those branches were engulfed by the slow rise of sphagnum moss. Such “layering” is a common mode of reproduction for black spruce.

When looking at a miniature grove of three-foot tall trees, it’s easy to forget that you could well be looking at an old-growth stand. If you look closely, you can tell that many of these trees grow barely half an inch a year— or barely ahead of the growth rate of the sphagnum moss at its base. That means that a three-foot tree could easily be twice that tall and may have been growing there for 150 years. But half of that original tree is located under the moss, down in the peat layer.

While black spruce is often found in pure stands in the more acidic and stagnant parts of peatlands, where groundwater upwelling raises the pH and adds a bit of calcium, tamarack will tend to outcompete the black spruce. It’s easy to recognize the patterns of water movement in most peatlands, by the sometimes abrupt changes in the makeup of tree cover. There are places in the Lost Lake Swamp where you can travel from a dense stand of black spruce into an open sedge meadow and back into a forest dominated by stunted tamarack within a distance of 100 feet. Water movement, or the lack of it, determines the surface vegetation.

The term “swamp” really doesn’t do it justice. Peatlands are remarkably complex and always interesting. Which, I guess, is why I keep coming back, season after season.

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