Frost crack

In late winter and early spring, water in the phloem, known as the inner bark and in the xylem, known as the wood, expands and contracts under often significantly fluctuating temperatures.

Other causes are the expansion of freezing water in cell lumens, and additionally the formation of ice lenses within wood.

[4] In winter when the sun sets or the sky clouds over, the temperature of the tree drops very quickly and as the bark cools more quickly and the wood contracts more slowly, the bark rips open in a long crack, sometimes with an audible report likened to a rifle crack.

[13] Frost cracks often act as sites of entry for wood decay organisms, including insects, fungi and bacteria.

Species such as crab-apple, beech, walnut, oaks, maples, sycamore, horse-chestnut, willows and lime are prone to developing frost crack given the right conditions.

[14] Avoiding the use of fertilizers late in the growing season can reduce the incidence of splits, also protecting the bark of young trees from physical damage such as that caused by lawn mowers, car bumpers, grazing animals, spades, trimmers, etc.