I was in Denmark and I got the chance to go into a forest. This was a few months after I got the beta and tried it out, and I will say that it looks very similar to the forests in this game (I even saw deer in the forest😛) The trails between forests were just like the roads in KC:D so if anyone is wondering, those forests are authentic. However, the one I saw was a little different because Danish forests are different from Bohemian forests.
Going to forests is precious experience these days.
Even the forests in Bohemia are not now what they used to be in 15th century. Too much coniferous trees (spruces, pines, etc.). They were commonly planted since 19th century because of they produce wood faster -> more profit in shorter time. A lot of noble families make a fortune of it - Schwancembergs, for example, had almost depleted Sumava forests.
The forests in the game seem pretty realistic to me - thumb up!