From Fortune Magazine on April 16, 2019:
The wood for the soaring cathedral was first felled around 1160 to 1170, with some of it coming from trees thought to be 300 to 400 years old at the time they were chopped. That puts the oldest timber in the cathedral at nearly 1,300 years old. Replacing those beams with comparable oak is simply not an option, said Bertrand de Feydeau, vice president of the preservation group Fondation du Patrimoine. Trees that supplied the roof’s frame came from primary forests, forests that are largely untouched by human activity. He surmised that the huge trees associated with primary forests are gone too.