Excellent question. You’re going to pick up some heat for this one (because no one likes to think their beautiful whatever is contributing to the destruction of the environment) but the moral thing to do is ask.
What ZMF says on their website is they only purchase wood through accredited dealers. I don’t know what that actually means, but I’m pretty sure
@zach915m will be along shortly to explain it.
If you still have concerns after that but want a pair of headphones made of renewable materials, consider maple, cherry, or other species that are sustainability grown and harvested with renewable protein leather earpads and headstrap.