Any tree that grows quickly will have thicker (less densely packed) rings. The author describes a planting strategy that "tricks" the trees into growing more quickly than usual, so my intuition is that those trees will be weaker than they otherwise would be. The choice of species just moves the "natural" density point.
growing forest quickly =/= growing trees quickly. I might have missed something, but I don't think he mentions anything about making the trees grow faster.
The "tricks" are to mature the forest (i.e. make it self-sustaining) within 10 years, tree growth-rate notwithstanding.
