Other articles (and the underlying research) actually mention this. It's suspected that the acidity killed off most of the younger, more temporary "new growths"

Other articles (and the underlying research) actually mention this. It's suspected that the acidity killed off most of the younger, more temporary "new growths" (like non-native grasses) in the area and provides suitable conditions for "old growth" plants to quickly expand into the area after the acidity dropped off.