by Judy Purdy and Janisse Ray
This summer, Paul Hendrix is "grunting" for earthworms and looking for answers in Florida's Apalachicola National Forest.
Kneeling on the forest floor, the UGA soil scientist rubs a car leaf spring across a wooden stake, creating a curious sound that brings large, pink earthworms wriggling to the surface. Unlike "baiters" who go grunting to collect fish bait, Hendrix just wants to ask worms a question: What exactly are they doing to the soil?
One of a handful of U.S. scientists who study earthworms, Hendrix is conducting a four-year probe on how worms contribute to the soil and to the health of this national forest.
"These worms are very popular as fish bait. People go in there in droves, pull out many thousands of them a day and sell them," Hendrix said. "The Forest Service is interested in what effects this may be having. Could there be some detrimental impacts of this on the forest itself?"
No one knows for sure, but Hendrix said he suspects worms are a major factor in maintaining a healthy soil and, thus, a healthy forest.
"The soil is our most important fundamental resource. What's going on in the soil is the basis for everything, whether it's agriculture, forestry or grasslands," said Hendrix, who teaches in both the UGA Institute of Ecology and College of Agricultural and Environmental Sciences.
Based on 10 years of worm research funded by grants from the National Science Foundation, the U.S. Department of Agriculture and the U.S. Forest Service, Hendrix knows worms are important to the biological and ecological processes that keep farm and grassland soils healthy. In addition to confirming what gardeners have long proclaimed -- that worms contribute to overall soil fertility -- his research shows they enhance soil structure, reduce erosion and may help restore soils heavily damaged by plowing and the use of chemicals.
He and his graduate students have found that farming practices can make a big difference in the number of worms that dwell in the soil. For example, no-till fields -- where seeds are planted with little or no plowing -- contained more than 500 worms per square meter; plowed fields, on the other hand, ranged from more than 100 worms per square meter to no worms at all, depending on the field's condition and how it had been managed in the past.
"When you stop plowing and start using a no-till conservation management system, things change in the soil," Hendrix said. "For one, earthworm numbers can go very high. The breakdown of organic material also is much faster where worms are abundant."
Their experiments also established that worms help make essential minerals in organic matter available to plants.
"It turns out phosphorus and nitrogen are probably the main limiting elements in a lot of these systems," he said. ""All the nutrient cycling that goes on has been shown pretty well in agriculture, but it hasn't been shown very well in forestry."
That's why Hendrix and his graduate students are now studying worms and their effects on nutrient cycling, soil fertility and plant growth in the Apalachicola forest.
"These real sandy soils [in the Apalachicola] don't hold on to nutrients very well," he said. "These worms could be having some influence on nutrient turnover in the soil and the availability of nitrogen and phosphorus."
Although the scientists are measuring to what extent worms contribute to healthy forest soil, they won't have any hard, fast answers for another season or two. Based on preliminary data, though, Hendrix said he sees no reason yet to be too concerned about short-term reductions of native worm populations that seem to follow baiting.
Eventually, his research will help the Forest Service determine how much baiting to permit in the Apalachicola as well as steer long-range management practices aimed at maintaining the ecosystem's diversity. Those include decreasing the tinder build-up through prescribed burning, which yields more lucrative baiting.
"The fire is important in keeping these forests the way they are, which in turn creates conditions favorable to these worms," he said. "The system takes care of itself; the understory comes back very quickly, and then [the baiters] don't bait in there anymore."
And Hendrix's research may shed light on a bigger issue: the natural history of native earthworms. Unlike many soils in Eastern United States, which are dominated by nightcrawlers and other worms from Europe and Asia, Apalachicola soils contain pure populations of native worm species. Many native worms that tunnel through the soil have yet to be described, much less studied, said Hendrix, who edited the book Earthworm Ecology and Biogeography in North America, published by Lewis Publishers.
"There are so many different species of worms around, and they do different things," he said. "We need to know a lot more about which species are present and what they are doing in wild-land ecosystems."
Take, for example, worms native to the tall grass prairie. They are better adapted than their European cousins to climate extremes. Hendrix has reason to believe these and other native species, including those in Apalachicola, also may be more efficient at nutrient cycling.
And that's why Hendrix spends so much time on his knees on the forest floor. He's bringing to light worm secrets that now lay hidden in the dark, damp ground.