Frogs offer signpost to farmland's wildlife impact

A leopard frog
A leopard frog, likely 4 or 5 years in age, hangs out in a researcher's net near Mantador, N.D., on Aug. 2, 2012. Researchers are looking at the relationship between the loss ofCRP habitat and the decline in amphibian populations in North Dakota, Minnesota, South Dakota and Iowa.
Ann Arbor Miller for MPR

Farmers are plowing up millions of acres of grassland and wetlands to put the land into crop production. The change could have great affect on wildlife populations.

Lots of frogs are a sign of a healthy wetland ecosystem.

"They're everywhere," said Justin Fisher, as he looks for frogs in a roadside ditch next to a wetland in southeastern North Dakota.

Today, Fisher is specifically looking for frogs with unusual color variations.

He plops a net over a frog.

"You see him? That's a real good one. Oh man, that just made my day."

Fisher, a graduate student at North Dakota State University, is studying the genetic diversity of northern leopard frogs. He is finding a direct connection between the amount of habitat and a larger gene pool. That factor is important for long-term survival of the species.

A young leopard frog
A young leopard frog explores the confines of a bucket after being caught on Aug. 2, 2012, near Mantador, N.D. The thumb of Justin Fisher, a graduate student at North Dakota State University, is also pictured. Fisher is researching the health of frog populations by looking at genetic tools.
Ann Arbor Miller for MPR

"Having that genetic diversity available with these populations increases overall fitness of the population and their ability to persist long term," Fisher said. "By harboring this large amount of genetic diversity you are enabling your populations to overcome adversity."

Adversity for frogs might be disease, or periods of drought when many wetlands dry up. Adversity can also be having wetlands plowed under and planted with corn or soybeans.

This wetland where Fisher is catching frogs is in the middle of a corn field. With a drier summer, the farmer has plowed edges of the wetland that in the past were too wet to farm.

"And that's just part of the cycle with these temporary wetlands like this one where it may inundate a wetland for a year or a few years, and with weather patterns they're able to take it back and it will now be planted," Fisher said.

This is a small change in the landscape. But the same thing happens in thousands of places across the region.

Some scientists say that kind of activity could lead to habitat loss.

David Mushet, a scientist for the U.S. Geological Survey, studies what happens to wildlife habitat as farmers decide when to take land out of the Conservation Reserve Program, or CRP, and return the land to crop production.

Mushet and other scientists developed a complex computer model that allows them to predict habitat loss. They analyzed what would happen if farmers convert all of the acres eligible to come out of the CRP program to cropland. Mushet said that would destroy 25 percent of amphibian habitat across the eastern Dakotas and western Minnesota.

Graduate student Justin Fisher
North Dakota State University graduate student Justin Fisher scoops up a leopard frog on Aug. 2, 2012, near Mantador, N.D. Fisher researching leopard frog populations and their health.
Ann Arbor Miller for MPR

CRP land reached a peak in our region in 2007. It's been declining ever since and the loss of habitat has accelerated as crop prices spike higher.

Amphibian populations are still very healthy in the region, Mushet said, but wetter-than-normal conditions over the past several years are masking the effect of habitat loss. That's because wet conditions created numerous temporary wetlands in farm fields.

"As we go into a drier period, we're going to lose that natural habitat that's available out there from being in the real wet period, combine that with losses of the CRP and I believe we might be setting ourselves up to see a big crash in the amphibian populations," Mushet said.

He said the double-whammy of habitat loss won't affect only amphibians. Waterfowl and grassland bird populations will likely also take a hit.

USGS scientists are modeling a variety of possible effects from the loss of acres enrolled in conservation programs. They even examined the reduced capability for carbon storage and flood water storage.

The overarching goal of this research is to help put a value on grassland and wetland habitat.

"And be able to see more of them retained in the conservation reserve program rather than being returned to crop production," Mushet said.

He said the ability to predict effects of habitat loss over a large area could help policy makers target conservation funding to the most valuable habitat.