https://en.wikipedia.org/wiki/Bletting
The idea that leaves and fruits completely magically vanish off trees in winter is pretty weird.
I think in a survival situation in winter it would not be unheard of to be able to rely on late-growing fruits and berries that either fall off and remain on the ground, or simply stay in the tree during winter.
Some fruits and berries are literally considered inedible unless they undergo a bletting process and the most natural bletting process is freezing.
Consider allowing atleast SOME fruit trees to continue to be foragad during winter to help with the fact that there is such a small amount of energy food and foragable food available during this time. All these foraged fruits and berries can be a "bletted" version of themselves, perhaps making them slightly less good, and some can get much better, like quince and medlar and other fruits that actually SHOULD be bletted before eating.

