Yes, I have heard that there are more trees today. Deer, however, love farms. There are far more deer today in America than ever before because of all the farms. This keeps them well fed.
Let’s not forget the complete lack of predators too. Wolves, bears and cougars used to roam over a much broader territory than they do today. The influence that they would have had on deer populations would have been significant.
According to this website: http://www.ardeerhunting.com/tidbits.htm American hunters kill SIX times more deer annually than EXISTED in 1900.