Within the Houghton Rhizotron, ecologist Alex Friend appraises a tangle of roots. The underground lab allows researchers a worm's-eye view of that half of a forest lying below our feet.
Within the Houghton Rhizotron, ecologist Alex Friend appraises a tangle of roots. The underground lab allows researchers a worm's-eye view of that half of a forest lying below our feet.
Centipede Rhizotron
The Houghton Rhizotron opens a window on a rarely seen world: a centipede squeezes between the soil and glass.
Earthworm Rhizotron
The Houghton Rhizotron opens a window on a rarely seen world: an earthworm curls up for a long winter's nap.
Slug Rhizotron
The Houghton Rhizotron opens a window on a rarely seen world: a slug lays its eggs in an underground nursery.
“We've got one of the strongest groups in the nation studying soils, and we're seeking to become a big dot on the map.”

USDA Forest Service Northern Research Station Forestry Sciences Laboratory

Alex Friend, Research Ecologist
afriend@fs.fed.us

Going Underground

It's been called science's last frontier: a source of miracle pharmaceuticals, a key to understanding global climate change, the dwelling place of thousands of mysterious, unknown creatures

This brave new world is the universe beneath our feet. And even though it's as intimate as the mud squishing up between your toes, soil is poorly understood.

That's because studying what's going on in soil is really hard. You can't see through it, and when you dig up soil to examine what's there, the environment is drastically disturbed. What you need, says Alex Friend, is a window into the earth.

The new Houghton Rhizotron is exactly that, times twenty-four. The seventy-five-foot tunnel into a wooded hillside on the Michigan Tech campus is virtually paneled with glass. Walk through its entrance, and on either side are a dozen steel covers almost as big as refrigerator doors. Remove one, and through the window inside you can see a tangle of roots, worm tunnels snaking along the glass, and a number of bugs, including a two-inch wriggling centipede.

"They are the lions of the soil," Friend explains. "They eat pill bugs and mites."

Researchers can remove any of the twelve panes of glass that make up each window, allowing direct access to the soil and the creatures therein. This day, however, the centipede remains safely behind the glass barrier.

With funding from the USDA Forest Service, the $500,000 Houghton Rhizotron was completed last summer. The facility is maintained by the Forest Services's Northern Research Station, headquartered in Pennsylvania, through its Belowground Processes Unit at the Forest Sciences Laboratory in Houghton. Friend, the project leader and a research ecologist, directs operations

The facility will allow research on topics ranging from carbon cycling and root growth to soil organisms. "There's a wealth of opportunity," says Friend. His latest research project involves measuring the seasonal death and regrowth of roots. "It tells us a lot about when trees are looking for water and nutrients," he says. "It's basic information on how forests work." Next, he'll be studying root-feeding weevils including where and when they feed. "We don't really know what their impact is," he says.

Anything that affects tree growth is magnified in importance as scientists attempt to understand the dynamics of global climate change. Forests withdraw countless tons of carbon dioxide from the atmosphere, serving as "carbon sinks" that may help mitigate global warming. As roots die off, they release some of that carbon into the soil. In addition, they exude sugars and other carbon compounds into the ground throughout their lives.

"The rhizotron will help us understand how carbon is transformed during this process," said Professor Kurt Pregitzer, director of the University's Ecosystem Science Center and the first to conceive of a rhizotron at Michigan Tech. "This facility allows us to take direct measurements of processes in the soil.

Most of the action occurs in the top few inches of soil, the home of an astonishing array-and quantity-of living things. "There's a mile of roots in one square yard," Friend says. In a clump of soil the size of a grape, you might find ten yards of fungal filaments of the sort that appear on moldy bread. "The upper four inches is where most of the biological activity takes place."

Most, but not all. Through another pane, an earthworm is visible, curled up in a little knot at the bottom of a tunnel about a foot beneath the forest floor; they routinely go to the bottom of their burrow in winter and ball up.

The lowly earthworm has become a hot topic in recent years. It has been implicated in the destruction of the deep layer of plant detritus found on the floor of many northern forests, where earthworms are nonnatives. While they play a key role in enriching the soil, by composting the thick layer of duff, earthworms may be endangering plants and animals that rely on that habitat for survival. "The rhizotron could help us better understand how they impact the forest," says Friend.

The rhizotron will help cement Michigan Tech's position as a leader in soil science research. "We've got one of the strongest groups in the nation studying soils, and we're seeking to become a big dot on the map."

"With the rhizotron, there's a wealth of opportunity here to study the world beneath our feet," he adds. "The sky is the limit."