Sustainable by Design

How do we get biomass from the land while preserving—or even benefiting—its living communities? Whichever course we take, researchers at the CALS-led Great Lakes Bioenergy Research Center are determined to put all pros and cons on the table.

Due to all this hypothesizing, a section of Arlington, the CALS agricultural research station 20 miles north of Madison, now resembles Jackson’s vision in miniature. Alongside traditional row crops like corn has sprouted a mosaic of switchgrass, shrubs like willow, an Asian grass called miscanthus and mixtures of prairie species. They are all auditioning for roles as tomorrow’s bioenergy crops, and the researchers are scrutinizing them from every angle.

Jackson’s students, for example, are examining nutrient use. “The neat thing about prairie grasses is they resorb nutrients at the end of the season,” Jackson says. After hitting their peak of growth in August, he explains, the plants shut down over two to three months, pulling nutrients and carbohydrates back into their roots for use again in the spring. Measurements by his group show that up to 70 percent of plant nitrogen gets recycled this way, suggesting that prairie species might need less fertilizer as bioenergy crops than does corn. By pulling nutrients from deep soil layers, their roots might also reduce nitrate leaching into groundwater and runoff into lakes and streams.

Bioenergy crops could also be a boon to birds and insects. Wisconsin alone hosts some 500 native bee species, most of which don’t form hives like the social European honeybees do. Instead, they’re solitary creatures, Gratton explains, that crawl inside cavities in trees, holes in the ground or dried stalks of flowers and grasses to lay their eggs. “They have nesting requirements that are very diverse,” he says, “and if all you have is corn and you’re looking for stem-nesters, you’re not going to find a lot of them.” But a lack of bees isn’t what is most troubling, he adds. It’s loss of the service they provide: pollination.

For his part, Kucharik studies one of the most critical services of all in this era of climate change: Locking away carbon in plant tissues and soils to cut CO2 levels in the atmosphere. Many people assume this will happen automatically so long as some kind of bioenergy crop is sucking up the gas, but the situation is actually more complex, Kucharik says. Take corn, for example. “Corn is actually great at converting energy from the sun, water and CO2 into plant biomass,” he says. “But it’s really the net soil storage in the long term that’s important.” Most corn biomass gets removed from the ground every year, he notes. And the rest is often tilled under, releasing additional CO2 as microbes are stimulated to break down organic matter in the soil.

Here again is where prairie species could shine: After all, their massive root systems built the Midwest’s fertile, carbon-rich soils in the first place. Even if they are widely planted as bioenergy crops, however, accumulating carbon will take a very long time—if it happens at all. “That’s really what we’re going toward in my research,” Kucharik says. “Will we store carbon? And if so, how much?”

Despite the caveats, many are still betting that biofuels will ultimately drive farmlands toward greater diversity and ecosystem health. The impact on forests, though, could be very different. In fact, CALS forest ecologist David Mladenoff fears bioenergy is taking them in the opposite direction.

For decades, Mladenoff has studied what keeps managed forests healthy and productive over time. And often, it’s variety, he says: sunlit gaps in the canopy, trees of different ages, and—critically—an abundance of stumps, logs, branches and twigs on the forest floor. Just as in farmlands, debris like this reduces erosion, stores carbon, recycles nutrients and creates habitat for animals and understory plants. But in the quest for new fuel sources, it has been dubbed “waste” and ripe for the taking—much to Mladenoff’s alarm.

“From my standpoint, we’ve spent much of the last 20 years learning that we need to be leaving more wood behind in the forest after harvesting, and now all of a sudden the movement is: We want to take the rest,” he says. “It’s in total conflict with what we know ecologically.”

Not that the intentions here are bad. In an effort to replace coal with cleaner, renewable energy sources, many states have built power plants that can burn plant-derived materials instead, such as scrap lumber, debris from timber harvests and cornstalks. Environmental groups have praised the move, but the power plants’ ravenous appetite for fuel is creating other problems. A few years ago, for example, Wisconsin set a guideline stating that loggers need leave only one ton per acre of woody debris behind after cutting trees—some three to eight times less than after a normal harvest, or what amounts to “a bunch of pen-sized twigs scattered around in an acre,” Mladenoff says.