The new energy development is "almost a spider web coming down to the forest," said Nels Johnson, of the Pennsylvania chapter of The Nature Conservancy, which estimates the state could see thousands of miles of new pipelines over the next two decades.Even northeastern states that have put a hold on fracking aren't immune, because many import natural gas. The U.S. Energy Information Administration found that 245 miles of new pipelines were laid in the Northeast last year, and that figure is projected to grow. Wind turbine development poses similar threats, too. The Nature Conservancy says Pennsylvania already has more than 600 of the giant blades, with the potential for thousands more in coming decades. The total acreage taken up by the pipelines, wind projects and related development isn't that large, but the open spaces they create allow predators and invasive species to permeate a canopy of trees that once kept them at bay. It's not hypothetical, scientists say. Studies and observations have documented invasions. And just as with humans, the uninvited guests change the neighborhood. Forest fragmentation opens the door to invasive species such as the cowbird, a type of blackbird that normally prefers open land, said Bridget Stutchbury, a biologist at York University in Toronto who studies forest songbirds. "The female cowbird sneaks around the forest, laying her egg in other species' nests," Stutchbury said. Forest birds such as thrushes and warblers don't realize the egg isn't theirs and expend energy raising chicks from another species in what she called a "nifty strategy for child-rearing." The droppings that cowbirds and other invaders leave behind can also contain seeds from invasive plants that will sprout, spread and ultimately change the soil so much that some forest salamanders and wildflowers can't survive, experts note. A report by the U.S. Geological Survey, released last week, found that in Pennsylvania's Susquehanna County, at the heart of the drilling boom, the number of patches or sections of forest increased by about 156 between 2001 and 2010, with Marcellus Shale drilling and related pipelines responsible for most of the change.