Here in Oulanka there is an uncharacteristic richness underfoot, a striking biodiversity, especially for a landscape that lies just a few miles south of the Arctic Circle. The main reason is limestone, an extrusion of youngish dolomitic rock—composed largely of carbonates—overlying the older granites and gneisses that make up the bedrock in so much of the rest of Scandinavia. The carbonate helps neutralize what would otherwise be acidic soils, and it adds critical nutrients. "Without the limestone," says Pirkko Siikamäki, head of the University of Oulu's Oulanka Research Station, at the heart of the park, "Oulanka would be just like the rest of Finland."
Instead, Oulanka is unlike almost anything else in the Finnish landscape, a place where a surprising number of biological zones converge. Because of its topographical diversity—high fells and low river valleys, mires, bogs, and alluvial grasslands—it is a kind of crossroads for species that normally do not overlap. Here is one of the few places where European, Arctic, and even Siberian species come together, mingling at the very edge of their ranges.
I came to Oulanka, as so many visitors do, to witness the grandeur of its glacial landforms—especially the canyons carved by the Oulanka River, which flows eastward through the park toward the border of Russia, just a few miles away. But the farther I hiked along the park's popular footpath, the Karhunkierros (Bear's Ring) Trail, the less I found myself noticing the major features of this landscape: the kettle holes—basins created by melting boulders of ice left behind by glaciers—or the gaping crevices worn away by the Oulanka River, or even the canopy of pine and spruce boughs overhead. Instead, I found myself lost in contemplation of the forest floor.
The word "floor" does not capture the intricacy, the complexity of this terrain. The word is too two-dimensional, too dismissive. This is not the flat, dry mat of needles you often find in the conifer forests of the American West. The needles you do see on the surface here—thrust aside by upspringing mushrooms or caught up in the leaves of a lingonberry—are like a roof of thatch on an interconnected, underground city. This is a place where the years can be measured in voles, especially the bank vole and field vole, which bore through the mass of low-lying plants at ground level. Some years vole numbers boom, thanks to abundant food and few disease outbreaks. A good vole year—plenty of voles everywhere—is good for just about every meat-eating member of the food chain: foxes, stoats, weasels, owls and other birds of prey. A bad vole year—and the past few years have been disappointing—is a bad year for predators in general.
In a sense, the forest in Oulanka is not made up of trees. The trees are woven together into a forest by the biotic community at their roots, by the stunning variety of beetles, plants, lichens, and mushrooms. These species are all sheltered by the canopy of branches above them, and in turn they help break down and circulate nutrients in the soil.