RENOVO, Pa. - For decades, natural-gas drilling has been part of the landscape in Sproul State Forest, a vast timberland in northern Pennsylvania pocked with hundreds of shallow wells and crossed by pipelines.

But Douglas J. D'Amore, the Sproul district forester, was unprepared for the massive size of the drilling operations that have moved into his forest in recent months to tap into the Marcellus Shale, the deep formation whose bountiful yields have triggered a frenzy that is transforming the way Pennsylvania's public lands are managed.

"Just the scale of this Marcellus thing is much bigger than anything I've ever seen," D'Amore said.

Anadarko Petroleum Corp. carved out four acres of red oak and maple forest, leveling a well pad about the size of three football fields to erect a 200-foot-tall drilling rig. The directional rigs are essentially mobile industrial operations: Each requires 80 trucks to transport, and it takes about a month to bore into the shale about 8,000 feet below.

"When you first see the size of the well pad - whoa!" said D'Amore.

Early-season bow hunters returning to their favorite spots this month were shocked to discover that Anadarko had already cleared about a dozen well pads in Sproul. Active rigs are posted as off-limits to hunting, and security staff ask anybody approaching the sites for identification.

"I'm sure I'll have a lot more complaints when deer-hunting season starts," after Thanksgiving, D'Amore said.

This is only the beginning.

Thus far, only three Marcellus wells have been completed on state forestland. But 660,000 acres of state forests are under lease, and state Department of Conservation and Natural Resources officials expect a rapid escalation in drilling.

"A year from now, there probably will be a hundred wells operating where there are only three now," said James R. Grace, DCNR's deputy secretary for parks and forestry.

Foresters, whose staffs were cut last month because of the state budget crisis, are girding for a management nightmare. The forestry bureau now monitors a few dozen drilling operations a year.

"We're going to go from 30 wells drilled a year to 800 wells a year," Grace said. "It's a whole order of magnitude."

Though geologists long have known that the Marcellus Shale contains natural gas, improvements in horizontal-drilling technology have made the formation suddenly accessible.

With vast reserves of Marcellus gas now in play, the economics of drilling on state land has changed dramatically in just a few years.

In 2002, DCNR offered 218,000 acres of gas leases in northern Pennsylvania for bids. The gas industry protested the then-exorbitant rate of $30 an acre and declined to bid for most of the tracts. Only a quarter of the acreage was leased.

Now, DCNR is seeking bids by Jan. 12 for six tracts totaling 32,000 acres and is asking at least $2,000 an acre.

"That's how much the world has changed in the last few years," Grace said. "Somebody would have made a killing if they had bid on those tracts in 2002."

Until 2007, the state's Oil and Gas Lease Fund had generated $153 million over five decades. Currently, there are about 750 producing wells on state land.

Last year, in a single auction of new leases, DCNR generated $166 million from 74,000 acres, surpassing the total generated in the previous 53 years. One of the tracts fetched $5,837 an acre.

Once the wells start producing, the state also stands to earn hundreds of millions of dollars from royalties, which are payments based on the market price of gas produced. Most of the old leases provide for the state to receive 12.5 percent in royalties, but in the latest round the state is asking for 18 percent.