Flying about 1,000 feet over Northern Pennsylvania, Nels Johnson looks down out of a small Cessna.“This is the biggest expanse of contiguous forest in Pennsyvlania,” he says. 

The plane soars over an area called the Pennsylvania Wilds. It’s a chain of state forests and game lands just north of Interstate 80. Johnson is studying the ecological impact of the gas boom. He describes the green expanse below.

“Large blocks of forest that have only a few highways going through them and a few gravel roads,” he says.

The expanse is crucial habitat for migratory birds, mammals, and fish. But the forest is important in another way. It sits on top of the Marcellus Shale. After a few minutes, we begin to see clearings in the trees. They’re packed with machinery and vehicles.

“You can see clearings all along here now. None of this was here two years ago,” he says. 

That was until the state, under Governor Ed Rendell, began leasing these areas to gas companies. The state needed money. And it got hundreds of millions of dollars to plug a budget hole. Gas companies have quickly moved into the green hilltops here, clearing land for drilling pads and pipelines. It’s the pipelines that concern Johnson the most. They could fragment large blocks of forest into smaller and smaller pieces. That’s why he’s pleased when he looks down and sees a series of pads built near a power line.

“A lot of this is right next to this electric line. The state actually did that on purpose, I think, to avoid fragmentation,” he says.

Back on the ground, Johnson explains that some species, like amphibians, orchids, and songbirds thrive in the deep forest. When land is cleared for drilling, the conditions they depend on change.

“All of a sudden you’ve got a lot more light, you have less humidity, often you have invasive plants that move in along a new edge,” Johnson says.

All of which can make it hard for some species to stick around. But how much drilling can these plants and animals tolerate? Can they live within a quarter-mile of a rig? A half-mile? Margaret Brittingham is trying to answer these questions. She’s a forest ecologist at Penn State. Brittingham has come to the Pennsyvlania Wilds, the same forest Johnson and I flew over. She’s set up a simple experiment in which she counts the birds near a well site, and compares that to a similar tally deeper in the forest.

“Basically, there were some species that were more abundant away from wells, and those were the forest species — the black-throated green warbler and ovenbird, and the only species that were more abundant near the wells were the robins. And that’s because they’re in the forests and they’re edge species,” Brittingham says.

She says no species are really endangered by Marcellus development right now. Riding on a forest road, Brittingham says that she wants to help the state and the industry keep it that way.

“One of the things we’ve got to think about is how do you reduce the time the pads are there and reduce the time they are so different than what the regular habitat would be,” Brittingham says.

So far, most of the Marcellus development is around the edges of the Pennsylvania Wilds.

But that could change. Governor Tom Corbett hasn’t said whether he’ll keep a moratorium on new leases in the state forests. His predecessor, Rendell, declared the moratorium after the state’s own scientists found that continuing to lease land would hurt the forests’ ecology.

But some in Corbett’s administration want to keep leasing forest. This wouldn’t be entirely out of step with how these forests have been used in the past.

“There has been oil and gas activity happening on state land since the 1950’s,” says Dan Devlin, the Pennsylvania state forester. Devlin explains that these woods were clear cut a century ago. They’ve now grown back, and the state is trying to protect the most fragile areas while drilling takes place. It’s a balancing act, Devlin says. For instance, keeping well pads next to roads is good because it reduces the footprint of drilling activities. But there are drawbacks.

“People driving along that road now no longer feel they’re in some sort of a wild country now you’re seeing this activity occurred,” Devlin says. 

The Marcellus activity was apparent on a ride through Tiadaghton State Forest with Dan Alters. He’s retired after a career in water management with the state Department of Environmental Protection. He lives just south of Tiadaghton state forest in Lycoming County. It doesn’t take us long to run into Marcellus activity along a forest road.

Alters passes a drilling pad, right off the road. Tanker trucks line the muddy lot. Soon he comes to stop. A drill rig is being moved. A woman working a flag trucks tells Alters, “We’ve got two oversize coming through the skinny part … Get comfortable.”

Alters is worried about drilling here. Mainly because it may impact his favorite place to fish, Pine Creek.

Alters heads to the creek on a recent afternoon. The water is muddy today, but it’s usually gin-clear. He walks to a spot and picks up a rock. “I’m looking for macroinvertebrates, but I couldn’t find any,” he says. Downstream of Alters are drilling pads. Above him are some of the best trout streams in the state. Unbroken forest around these streams keeps the water frigid, perfect for the native brook trout. Alters says gas development would change that.

“If you open up that forest, the ground gets warmer, the water gets warmer, and the streams obviously get warmer at the same time,” Alters says.  

This would make the water too hot for his favorite fish.

“I think in 20, 25 years, this area’s going to be grossly degraded,” Alters says. “I think trout fishing in many streams is going to be marginal, if it even exists at all.”

Alters’ concerns point to a basic question: can a forest be open for drilling and keep its wild nature? The question lingers with Nichole Deeghan. She tends bar at the Pine Creek Valley Lounge in Waterville. Extra business from off-duty gas workers helps. But she hates what’s happening in the woods she grew up visiting. Some of her favorite lookouts in the forest are now off-limits because of drilling. She wonders if the changes are permanent.

“What’s it going to be like in 20 years when my kids are groing up in the area?” she asks. “Are they going to be able to enjoy some of the things I get to enjoy?”

Drilling will almost certainly change the ecology of these forests. The question now is, how much?