During the bitter winter months in the northern hemisphere, trees have to endure drought conditions much like their counterpar in teeming hot deserts.
The ground is frozen solid with snow and ice, making it impossible for trees to draw out any water for their nourishment Trees therefore, have to subsist on the sap already contained in their leaves. The best example of this is to be seen in the needles of the pine tree.
If the sap in a leaf freezes the leaf will expand and burst. Pine needles, however, contain very little sap so there is little liquid to freeze. And water vapour does not escape easily
through the stomata of the pine needle as these are sunk in deep grooves.