This seems to imply that the founders of the college consciously had the trees planted because they knew the ceiling would need replacing the beams centuries later, and that their intention was that their successors would use those very beams that had been planted for exactly this purpose hundreds of years before.
It’s a fascinating thought, but OTOH it could just be that the 19th century carpenters thought it would be a nice gag if they used trees just as aold as the ceiling they were about to repair, so they searched for a forest that had been planted in 1386 and cut it down.
So what? The text clearly suggests that there was conscious planning involved, but being a pessimist and misanthrop I don’t credit mankind with that much foresight (and the devotion to preserve those trees throughout the centuries for the purpose they were intended for). Anyone knows more?