I can't speak to the timber situation of PA at the time the area was settled. There's a good chance the area was timber-sparse due to its proximity to the large cities along the eastern seaboard. Timber companies most likely came in, clearcut the timber resources, and settlers flowed into this newly opened landscape. Also, early farmers were probably not well off, and stone fencing was probably the most economical solution save for the time and labor involved. If you had a bunch of kids, as many farm families did, it was pretty easy to send them out to collect stones. I'm in the Driftless Area (unglaciated) of Wisconsin, and I generally never see stone walls. I do occasionally find concrete fence posts, as that was likely the most economical approach to fencing. Historically, it was mostly open prairie and savanna, so what limited building supplies were available went into the house and the barn.
It's interesting to note that the area east of the Mississippi River is more forested than at any point since European settlement. As an ecologist I am always studying land changes over time, and those changes seem to have accelerated in the 1970's. The absence of fire, both natural and anthropogenic, combined with the explosion of industrial agriculture have made profound and almost unbelievable changes to the landscape. It's what make restoration ecology a real pain; restore back to what?
JP
