Ecologist John Parker walks through a corn field beside a stream. The water flows into the Chesapeake Bay six miles south of Annapolis.
This spring, instead of corn, Parker and his fellow scientists at the Smithsonian Environmental Research Center have planted an alternative crop: eighteen thousand bamboo poles. Each is marked with colorful flags -- orange, blue, red, and yellow.
These colors signify different species of tree saplings that Parker is planting --- red maple, tulip poplar, American elm, hickory, and a dozen others. He is creating a diverse, native forest to replace a monoculture of corn, which requires lots of chemical fertilizers that seep into the stream and pollute the Bay.
I think I’ve dug about 10,500 of these holes out here,” Parker said. “This is a gas powered drill that has a four inch bit on it, and we take this down about 12 inches deep, and we do that on every plot 255 times.”
On this chilly, windy morning, he has a bit of trouble starting his drill.
But eventually, it roars to life and his new forest grows by one more tree.
Now, most people already know that forests are better at absorbing water pollution and carbon dioxide than farms, housing developments, parking lots – or just about anything else.
But not all forests are created equal. Surrounding this field, for example, is a forest dominated by tulip popular and sweetgum trees. Parker plans to monitor the soil and nearby stream to find out if a mixture of up to a dozen tree species is better at gobbling up pollution than forests with just one or two types of trees.
He also wants to know if a diverse forest can better survive environmental threats, like invasive species.
“You might think of elm trees, which were widely planted as shade trees throughout many of the cities of the U.S. and wiped out by Dutch Elm Disease,” Parker said. “We are thinking the same things might happen now to green ash trees which replaced many of the elms, which are highly susceptible to the emerald ash borer, an introduced insect from Asia."
A mixture of trees may be more resilient, because not all pests prey on all tree species.
But you may wonder: why would a diverse forest be better at soaking up water pollution?
Because of what you can’t see above the ground.
Dig a few inches below the soil, and you enter a subterranean jungle. A single acre of topsoil dances with a metropolis of life that includes 900 pounds of earthworms, 1,500 pounds of bacteria, 2,500 pounds of fungi, algae, arthropods, and even moles.
The fungi, in particular, are a little-known secret weapon for breaking down water pollutants like nitrogen.
“There is really an enormous amount of fungal biomass that is underneath these trees that is sort of helping this whole ecosystem work,” Parker said.
Mycorrhizal fungi look like tiny white threads. They live on tree roots, and enjoy a symbiotic relationship with the trees. It is hard for trees to get nutrients out of the dirt. But it’s easy for their fuzzy conspirators, which suck up nitrogen and give it to the trees. In return, the trees provide water and sugars the fungi can’t get on their own.
Theory is, the more trees, the more fungi. And the greater diversity of trees, the more diverse and potent the invisible web of fungi that pull pollutants out of the soil and clean up the stream nearby.
