Wild Ginger, Ants and an Old Paradox

By Lawrence J. Winship Gazette Contributing Writer

Each spring I wander my favorite haunts in search of ephemeral spring wildflowers. Patches of adder’s tongue, trillium, bloodroot, wild ginger, bleeding heart and spring beauty can be hard to find, but are so rewarding. These reliable harbingers of the deep forest shade to come are locally rare, mainly because of past land use practices. Widespread forest clearing and plowing in the 1700s and 1800s killed native plants and depleted their seed banks, wiping out local populations. Re-establishment of spring ephemerals requires at least two things: plants in nearby non- tilled areas to serve as seed sources, and time—lots of time, because seed dispersal is often a slow process.

Like 30 to 40 percent of the forest floor species in our rich woods, wild ginger, trillium and other spring ephemerals are dispersed by ants. Ant-dispersed plants, termed myrmecochores, have an energy-rich treat attached to their seeds. Called eliasomes, these little wing-like structures are oil-rich and motivate the ants to carry the seeds back to their nests, where they strip off the oil drops and toss the seeds aside. Seeds are dispersed and planted all in one process. Energy-rich external seed structures and ant dispersal can be found all over the world, in many different plant families, so we think this commensalism has evolved thousands of times. In our region the ants doing the harvesting and gardening are foragers. And although ants are certainly diligent in finding and gathering seeds, they don’t carry them much farther than about one meter per year. So it is that many regrown forests, which might support these plants, have none—they just haven’t gotten there yet, even after hundreds of years.

Because of this limited dispersal capability, spring ephemerals are central to a puzzle, called Reid’s Paradox, that has challenged ecologists for many decades. In The Origin of the British Flora, published in 1899, paleontologist Clement Reid wondered how oaks had recolonized his native England after the glaciers melted. If acorns simply plopped and rolled, how was it that they had covered hundreds of meters and even crossed the English Channel in time? Even squirrels don’t bury acorns very far from the tree. He estimated that it would take a million years to cover 600 miles—clearly, something else had been going on.

In the same vein, many trees we now consider New England hardwoods re-inhabited our region after the glaciers melted roughly 12,000 years ago. Evidence of plant migration can be read from pollen in layers of muck at the bottom of ponds, showing us that most species came from distant unglaciated areas in the mountains of Alabama and Arkansas. While a few species may have come from closer coastal plains now recovered by the Atlantic, or from Midwestern ice-free areas, most had to travel thousands of kilometers. How did they manage this in only a few thousand years?

For trees that produce large seeds of great interest to mammals and birds, it appears that only a few rare, long-range seed movements, in paws or claws or craws, are needed to put together, on average, a journey of one kilometer per day. The steady yet patchy expansion of beech trees and oaks northward is clearly evident in the pollen record. Perhaps you have seen a blue jay at work caching beech seeds in a circle, many meters from a convenient evergreen tree. One can readily imagine the hop-scotch needed for birds and trees to follow the ice sheet north.

 

But our spring ephemerals don’t readily fit that model. Try as we might, ecologists have yet to identify an animal, or phenomenon (hurricane? tornado? flood?) that can provide the occasional “big leap” needed to explain the movements of wild ginger. The genetic evidence is clear—our local populations of wild ginger came here from the southern mountains—but how?

My friends would probably agree that I am a bit of a romantic—I love a good story. So here is one to explain these unexplained plant distributions—no evidence, but…. Looking at my garden this morning I see bloodroot, violets, trillium, all put there by me, purchased at Nasami Farm in Whately. How different, really, am I from those people who lived in New England before the arrival of Europeans? I love plants, I am a gardener—were they gardeners, too?

We already owe our native brothers and sisters an enormous debt for creating and continuously cultivating maize over thousands of years. Our modern corn is a primary source of calories in most animal food, showing up in all kinds of meat, as well as in processed foods cooked in corn oil or sweetened with corn syrup. So most of the calories in our diet, for better or for worse, come from plants descended from “Indian corn.”

Might it also be true that the wake robins, wild ginger and bloodroot that lift my spirits each spring are also gifts from native gardeners, people who walked this land, and cared for it, long before my ancestors arrived and made so many changes? Many spring wildflowers also have medicinal properties, and they are also just plain delightful—reason enough, I think, to carry them north. I know I would.

Lawrence J. Winship, a member of the Hitchcock Center board, is a professor of botany in the School of Natural Science and director of the Southwest Studies Program at Hampshire College.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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