The strength of the downwash from the twin engine MV-22B Osprey is very graphically illustrated here in this YouTube video taken over Memorial weekend, May 2010 in upstate New York.
Another view of the same event here
Fortunately there were only minor injuries.
One for you arborists.......
Is there anybody out there?
Considering how long the downwash was for, one can't help but to wonder if the pilots considered aborting landing.