DougE has it right about managing for the carrying capacity of the habitat. And the way its done is to manage for "worst case". For instance you redue the herd to 20 deer per square mile - if that is all the deer it will support in a BAD winter. Sure some years are mild, and it would be possible to support more deer in those years - but the lower population also gives the habitat to regenerate.

In my are - we get a decent amount of snow - (150"ish) per year mostly in DEC,JAN, & FEB. We have a fairly high deer population - 30ish deer/square mile - sometimes a little more. We also have decent agriculture with dairy farms (not as many as before though). So most of our deer don't die in a bad winter - They usually have less fawns as a result.

FH