HARRISBURG - A series of topographic maps shows the impact of an estimated 54 Marcellus Shale well pads being drilled on 65,000 acres of the Tioga State Forest during the next five to 10 years.

These maps provide a visual representation of how drilling can change the composition of forest land that is considered primitive, semiprimitive and semideveloped.

The analysis by the state Department of Conservation and Natural Resources indicates a loss of 8,171 acres of primitive land, loss of 5,374 acres of semiprimitive land and gain of 13,545 acres of semideveloped land among the total acreage affected by drilling operations in that forest.

Tioga State Forest in Tioga and Bradford counties is ground zero in the debate over natural gas drilling in Pennsylvania's state forests. While drilling for shallow deposits of natural gas has gone on in the state forests for the past 60 years, the deep drilling in the Marcellus Shale formation is raising new questions about the short-term and long-term impact on the forest environment.

The DCNR map surveys are part of the evidence used to support Gov. Ed Rendell's new executive order placing 800,000 acres of state forest land in the Marcellus Shale off-limits to future leasing for natural gas drilling. This includes land designated as wild and natural areas, old growth forests, environmentally sensitive habitat and 88,000 acres in the Poconos where ecotourism is developing.

The governor said additional leasing beyond the 700,000 acres of state forest land in the Marcellus Shale formation already leased out will make it difficult to manage the forests in a sustainable manner.

The maps on the state Bureau of Forestry web site at www.dcnr.state.pa.us/forestry (click on mineral resources) show the estimated location of the 54 Tioga well pads, each of which would cover 10 acres according to DCNR and contain numerous wells. Then the maps are layered to show access roads, the changes in specific areas identified as primitive, semi-primitive and semi-developed and how that affects the forest's wild character.

The state forests operate under a multi-use policy, which means there are remote areas designated as primitive for a backwoods experience and nonmotorized recreation like hiking, semi-primitive areas with limited timbering and gas drilling activities and semi-developed areas with timbering and gas drilling and recreational use with ATVs and other vehicles.

DCNR is focusing on the 160,000-acre Tioga State Forest because that's where most of the Marcellus Shale drilling on state forest land is happening, said agency spokeswoman Chris Novak. Fifteen of the 25 Marcellus Shale wells drilled so far on state forest lands are located there.

Tioga State Forest is criss-crossed by Routes 6 and 15 and near the famous Pine Creek Gorge, often referred to as the Grand Canyon of Pennsylvania.

Like many state forests, most of this acreage was owned by lumber companies and land-title firms before it was purchased at cheap prices by the state. In the heyday of the lumber area, this area supported large sawmills. The first state purchases of land were made in 1900 to protect the headwaters of Pine Creek.

The survey identifies the Reynolds Spring Natural Area, which boasts stands of aspen and oak, as a primitive area that could be vulnerable to drilling. Overall, DCNR estimates the already leased state forest lands could include 1,000 well pads, containing 10,000 wells, in thirty years assuming full development. The agency's most recent lease covered 32,000 acres last January.

Senate Republicans are raising several issues concerning the need for the moratorium and its legality.

DCNR had been prepared to lease more than 80,000 acres in 2009, but only put up 32,000 acres for bid, meaning there is probably additional acreage that can be leased, said Patrick Henderson, executive director of the Senate Environmental Resources and Energy Committee.

He said DCNR included 18,000 acres of wild and natural areas in state forests in those leases and took precautions in the lease agreements to prohibit surface disturbance of that land.

"The premise that special protection areas cannot be leased at significant value, while still protecting the integrity of the land by prohibiting surface disturbance, is defied by the governor's own actions," Mr. Henderson said.