I remember that ents were tuned to take the winter a bit more harshly.
Well, the ents shouldnt be the only ones to suffer from a winter.
For.ex. Thrikrens are incects, and incects dont take winter so good,
Their bodytemperature lowers and the have a harder time to do anything.
Ever seen a bee in the winter outside?
Anothers are lizards (in bat, lizardmen). They like warmth very much.
Thats why they just sit in the sun, on a rock (in rl). During winter they
usually hibornate.
These are just examples. Either remove the ents wintertune or tune
the other races too. (Not just with the method "ents roxor too much
lets downtune them somehow" and then finding out what trees dont like)

Dont shoot the messenger. (and i apoligize for the bad grammar)

Wizards mix realism/fantasy as they wish. Dont get thrilled too much
with your realistic ideas. Main reason for tuning is not realism,
but trying to balance races.

And also - if here is 'a lizardman race' - it doesn't mean the race is
lizarman like... I mean they are more like humans with some lizard abilities
(walk with 2 feet, have hands and so on) - the same way as race 'duck' has
human figure.
So if lizardman doesn't suffer from winter - it's kinda same thing that
ducks aren't shot at autumn.