Underneath Florida pines, gophers are getting weird
Gopher burrows are full of roots. Does that mean they're farming the forest floor?
The southeastern pocket gopher is a fist-sized, chubby cheeked, elusive neighbor, but landscapers (not to mention golf course groundskeepers) in the sandy plains of Alabama, Georgia, and Florida despise the rodent for its tendency to burrow into lawns. “People go to great lengths to kill these things,” says Jack Putz, a forest ecologist at the University of Florida.
But there may be a lot more to those mounds than meets the eye. In a new paper based on observations of the gophers in a patch of long-leaf pine forest in Florida, Putz and a recent undergraduate, Veronica Selden, argue that the critters are actually farming grass roots for food.
The construction of those long, subterranean tunnel systems that pocket gophers call home present a mystery. Each individual keeps its own network, which can stretch for hundreds of feet, and defends it fiercely. Clearing all that soil requires a huge amount of energy—a fact that Putz and Selden now know much better than they’d like to. “We moved dozens of cubic meters of soil trying to isolate tunnels,” Putz says.
Simply eating the roots found along each tunnel system wouldn’t be worth the energy required. “Something didn’t click,” Putz says. Every meter of tunnel a gopher dug would cost it about a tenth of its daily caloric needs. For a human, that would be like needing to stop to eat a full-size candy bar for each meter dug. “If they depended on the roots they found while digging, they’d starve to death very quickly,” Putz explains.
But luckily, Putz was dealing with plumbing problems at home. Plant roots had infiltrated their sewer, which got him thinking. “The sewer line is pretty similar to a pocket gopher tunnel,” Putz says. After a gopher cuts its way through the mat of roots, they suspected that new, edible growth would push its way into the tunnel, creating a self-replenishing larder.
They couldn’t figure out how quickly the roots were growing with the gophers in the tunnel, though, or how much food they could actually provide. And the gophers were almost impossible to keep out while they tried to take measurements. The team started by digging a pair of trenches on either side of a tunnel, then blocking it off with plywood, then with sheet metal—but the industrious rodents always managed to dig around those barriers. Finally, they learned that they could surround a section of tunnel using an open-ended metal barrel, stopping the gophers from digging in from any direction.
Once successfully shielded from gopher teeth, roots did indeed begin to grow into the cavity—enough roots, the team estimated, that a typical tunnel network could supply 20 percent of a gopher’s foraging needs at any given time.
Putz suspects that that’s an underestimate. “I think we never hit places in the soil where roots are most abundant,” he says. “And having been outsmarted by pocket gophers on several occasions, I do believe they’re very wise in where they excavate tunnels, like any foraging animal.”
Previous research from another of Putz’s students has shown that the soil beneath a prairie can hold a bonanza of fat and starch. The wildflower blazing star grows from a bulb, while butterfly peas have small tubers. “Some of them were up there with potatoes” in terms of edible carbon, Putz says. Just a few of those payloads would cover the cost of a day’s dig.
Here’s where things get controversial: Based on those observations, the researchers write, “southeastern pocket gophers are employing a low-level food production system that may qualify as farming.”
Humans have invented agriculture over and over again on almost every continent. And several species of insects—ants, termites, and various beetles—have developed their own forms of farming by tending fungal gardens. But this would be the first time another mammal has been shown to reap what they sow.
Putz and Selden argue that gophers appear to create a microenvironment that favors root growth—by aerating soil and pooping all along the length of the tunnel. When the researchers isolated stretches of burrow, root growth slowed down, further suggesting that the rodents play an active role in crop yield.
Part of why Putz sees this as farming, he says, has to do with his experience conducting research in countries with a history of forest agriculture. Those managed forests look wild to someone who isn’t familiar with the trees—but the entire landscape is the product of human management.
It all comes down to how you define farming, Putz says. “If your definition of agriculture is based on seed farming, then no, they’re not out there planting. But they’re ecosystem engineers, definitely, because they’re creating conditions that are good for their crops, they’re pruning them, they’re fertilizing them, they’re doing everything but planting.”
But Ulrich Mueller, an entomologist at the University of Texas at Austin who studies insect agriculture, says in an email to Popular Science that describing gophers as farmers seems “premature.” He says that farming relies on four key traits: an animal has to specialize in specific species; promote its crop by watering or fertilizing; occasionally transplant it; and protect the crop from diseases, other grazers, weeds, or other dangers. That’s what we see in ants.
He notes that the paper doesn’t demonstrate that the specific conditions of the burrow actually cause a growth spurt in roots, nor that pocket gophers necessarily depend on in-burrow larders to survive. “Best research practice here would be to collect more data, rather than rush to publication,” he adds.
Mueller makes a comparison to bison. Migrating herds of bison fertilize the same prairie grasses that sustain them with their dung, and they also aerate the soil with their feet. But “it would be silly to call the buffalo ‘farmers,’” he says.
But focusing on what constitutes a farmer might be beside the point. Animals, and especially humans, can dramatically reshape the landscape to suit their needs without actually reinventing agriculture. Indigenous people in the Southeastern United States may have moved pecan trees as early as 8,000 years ago, and relied on the nuts for thousands more years, but they didn’t necessarily tend those plants. And plenty of cultures have regularly burned landscapes to favor a suite of easily harvested foods.
All of those strategies are forms of ecosystem engineering and interspecies reliance. At one end of the spectrum is intensive farming in fields—or even ant colonies. But the other side of the spectrum can still shape forests, streams, and whole landscapes. We may not know exactly where to place pocket gophers, but one thing is clear: they’re reshaping the grassland above them as they dig.