Summary Some trees suffer frost cracks when temperatures drop only a few degrees below 0°C, while others remain whole even below −40°C. Tree species such as those of the genus oak (Quercus) crack more than others, but no species appears to be immune. Why some stems crack when others in the same environment do not is not exactly known. Internal freeze-drying of wood, due to migration of moisture out of cell walls into cell cavities, certainly contributes to the formation of frost cracks; the drying involves freeze shrinkage which tends to be larger in the direction of wood's growth rings than along the stem's diameter, and progressively increases as temperatures decrease. Freeze shrinkage should not be confused with thermal contraction; moist wood does not contract during cooling as long as its moisture remains in cell walls. At decreasing wood temperatures in some stems, ice accumulates between wood cells to form ice lenses or ice layers which pry the tissue apart. The expansion of freezing water contribu...
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