I watched that documentary recently. I thought it was well done.
We are seeing the abnormal soil Ph here in the mountains of south-east Tennessee too.
The soil used to be very acidic here, naturally, but also from decades of acid rain and over a century of copper mining (sulfuric acid as a by-product). Now we are getting into the neutral range (Ph=7) in a lot of places. The local native acid loving plants, like mountain laurel and rhododendron, don't like it.