In Illinois, the natural reproduction limit seems to be about Springfield IL, a little north of an east-west line through Saint Louis, MO. Just from killing first year seedlings in my back yard, I think with Bald Cypress, seed needs heat to sprout, often not sprouting until late June, sometime early July. In my yard, north of Chicago, south of Milwaukee, seedlings sprouted in late June are not winter hardy by autumn. Seems growing season is too short to mature young seedlings. Usually by 2nd or 3rd summer, seedlings are fully winter hardy in the ground in my area. The issue is the seed seem to need 80 F heat to sprout, which means in northern areas they just don't sprout in time to harden off in spring. Plants older than 2 years send out foliage between the time the maples leaf out and before local oaks leaf out, not as much heat needed to leaf out as to sprout seed. So once established seedlings are just as hardy as adults. But this can explain the natural distribution of the species.
Knees, the article posted by
@armetisius doesn't mention bald cypress, but I could speculate the knees would make it difficult for mastodons and mammoths or even herbivorous dinosaurs to walk around the tree and eat foliage. - but that is shear speculation on my part. AND if this were the "purpose" of knees, why is it that knees don't appear normally until trees are over 25 or more years old. One reference I read said knees don't develop until tree is over 70 years old, but then I drove past a hedgerow of BC that was clearly man planted, and the house they were near was no more than 40 years old, trees looked 40 years old, and yet they had well developed knees. So obviously they can make knees younger than 70 years old. But if the knees were to prevent predation by large herbivores, the knees should appear sooner, not later in the BC life cycle. They definitely are a trait of only fully mature trees. So who knows why they make knees?