I've often wondered and even asked about this, and I'll continue to defer to the likes of Tom D and Ward on the answer, but when they write that PV "wasn't that way [tree lined corridors throughout] at all when it was built", I have to ask:
And what did the architect(s) and early club members think was going to pop-up there over time, apartment buildings and windmills?
I mean, PV is as close to a labour-of-love and one man's vision as any great design in America, and its membership has always been small and historically aware and justifiably proud of what Mr Crump (with help) created there, and the original site was naturally/heavily forested before any work began. So:
The day it was finished and open for play, and then for years afterwards, is it likely that those who most knew and loved the course and were closest to it thought to themselves:
"You know, Bob, it's great and I love it, but let's throw Mr Crump's vision out the window and start planting trees absolutely everywhere -- you know, to get that claustrophobic closed-in feel"?
Shouldn't we stop saying about courses that we think have/had too many trees (Olympic is another that comes to mind): "I've seen photos, and on the day it opened all you saw was open space...oh, and maybe some small saplings along the fairways"?
Peter