The flute-like notes of a hermit thrush wafted through my bedroom window. “Whyyyyy don’t you come with me?” he sang in a rising scale. I didn’t even open my eyes in the pre-dawn gray, but I did smile to myself. Spring has felt slow this year, because of the long period between snowmelt and green-up, but it is finally here.
My favorite way to celebrate spring is with a hike up St. Peter’s Dome in the Chequamegon-Nicolet National Forest. Gentle slopes, plentiful moisture, deciduous trees, and interesting rocks enrich the soil, which supports an amazing array of wildflowers. In comparison, the sandy hemlock grove near my house is a barren desert. The evergreen shade there doesn’t allow enough of the sun’s energy through to the forest floor to support much of a ground layer.
I suspected that I might still be a little early for the majority of blooms, but I just had to see what was up. Cut-leaved toothwort, blue cohosh, wood anemone, bloodroot, and wild leeks all poked their little leaves and buds out of the floodplain of Morgan Creek. The pale, fuzzy leaves of wild ginger were just beginning to sprout from its horizontal stems (called rhizomes) that snaked along, half-buried in the rich, moist soil.
The wild ginger caught my eye because its rhizomes were more bare than usual, with just a few cloaks of leaves here and there. Crouching down for a photo, I wondered if it was the foot traffic of people avoiding a mud puddle, or some other culprit that caused this exposure. Then I moved a little clump of dead leaves, and the tiny, pinkish point of an earthworm shrank away from the sunlight. Ah ha!
While European earthworms (brought here with ship ballast or in root balls) are wonderful at breaking down organic matter and mixing the soil in our gardens, they are just too efficient for the plants in our woods. Our northern forests evolved in the absence of earthworms, after the glaciers froze them out. Many plants here need thick, slowly decomposing leaf litter to grow, and for their seeds to sprout. In this exposed patch of ginger rhizomes, with the continued possibility for nighttime frosts and a lengthening drought, it is easy to see why fallen leaves are important.
Repercussions of the worms’ voracious feeding extend throughout the forest. The three-leaved clumps of trilliums unfurling themselves along the trail, with white buds that will be open by the time you read this, decline in worm-infested habitats. Other common summer plants (just now emerging!), like arching stems of Solomon’s seal, the thickets of wild sarsaparilla, and even sugar maple seedlings—the next generation of maple syrup—are also at risk. In their place, a lovely, green lawn of Pennsylvania sedge fills in among the trees.
With the lower diversity of plants on the forest floor, ovenbirds (a vociferous, ground-nesting warbler) are much more susceptible to nest predators like squirrels and other birds. One study, conducted in the Chequamegon-Nicolet National Forest just a few years ago, found that ovenbird numbers decline by about 25% in worm-infested maple forests. Happily, the same research project also found that three other species of ground-nesting birds—the hermit thrush (who woke me up), black-and-white warblers, and veery—are not affected by earthworm invasions.
As I put more space between me and the trailhead, the signs of worms faded quickly. Tiny, white, pants-shaped buds of Dutchman’s britches readied themselves for opening next to pink-striped spring beauties that were already attracting bees. Tiny leaves at the tips of chokecherry twigs glowed crimson in the sunlight. We all warmed up in the strengthening sunlight and on the steepening trail.
Spotted salamanders have already returned to a vernal pool just under the top of the Dome. Their clusters of round eggs—clear with black centers—rest among films of algae, layers of leaves, and tiny, wiggling larvae. I didn’t see any signs of worms up that high, which is fortunate. One study looked at the response of salamander populations to earthworm invasions, and found that “Salamander abundance declined exponentially with decreasing leaf litter volume.” Salamanders need lots of leaf litter to house the tiny critters that they eat.
These woods are changing – by the century, the year, and the hour. Some changes – like the graceful unfurling of petals, the delicate emergence of leaves, and the lyrical return of warblers—are welcome. Other changes may be more troubling.
“Oh, to love what is lovely, and will not last! What a task to ask of anything, or anyone, yet it is ours, and not by the century or the year, but by the hours.” –Mary Oliver, Snow Geese.
|Trilliums decline when earthworms invade their habitat. Happily this one is still surrounded by a healthy carpet of leaf litter. Photo by Emily Stone.|
|The rhizomes of this wild ginger plant lay exposed to the elements because earthworms ate their blanket of leaves. Photo by Emily Stone|