There is a RNG element to it. Beech will often drop more than one seed. As such if you cut down 100 trees you will usually get 75-100 seeds. BUT... you can cut down 10 or so in a row and get nothing.

With Birch I haven't cut enough to see... but it does seem to be an unsustainable. Pine and Fir also have always come off feeling unsustainable in the number of seeds to trees cut down. I don't have long term data on that though.

With Beech.. if you cut down 100 you should be able to regrow, cut down, regrow repeat at least 275 trees in addition to the original 100 and that is if you are really unlucky.