In winter, cracks form on the trunks of many trees. They can be large or small, wide or very narrow. Since they appear in severe frosts, they are called frosty. Wide cracks are also called frost ridges. All such injuries have one thing in common. They are located vertically and slightly at an angle. And there are very good reasons for this.
Take a closer look at the cleaned log. You will see that it is not solid, but consists of individual fibers. They stretch along the trunk. Perfectly straight lines are not so common in nature. So in a growing tree, the fibers are not located strictly vertically, but at a certain angle. At the same time, the places of their connection are far from being as strong as they themselves.
Consider the tree stump. On the saw cut it is very clear that the wood is not uniform. You can see the core and the annual rings around it. Wide, narrow, light, dark, but they indicate that the density of wood at different distances from the core will be different. And accordingly, the resistance to its external conditions is also not the same.
Remember how different substances behave when the temperature drops sharply. They tend to shrink, and the intensity of this process cannot be the same. The upper layers of wood, which are in direct contact with the outside air, are compressed faster and sharper than the inside. In addition, they protect the part of the trunk underneath.
Cracks often form in spring. The reason is sharp temperature fluctuations. Even when the tree is dormant, there is moisture in the wood. When the temperature drops below zero, it freezes, and accordingly - changes the volume and breaks the wood.
Why doesn't the crust burst horizontally? Take any fabric with long fibers. Try to separate these fibers from each other and then tear them apart. They are likely to be much more durable to break than when trying to split into separate long threads. It is the same with a tree. A slack is formed between the individual "threads".
Wait for warmth. You will see that with the onset of spring, small cracks will not even leave a trace. All layers of wood under the influence of high temperature return to their previous volume, and it is impossible to notice the damage with the naked eye. Over the summer, the crack will even have time to overgrow with a thin cambial layer. However, there is no reason to hope that it will drag on at all. In the next harsh winter, the crack will form again, and even become larger. Therefore, gardeners usually close up frost holes with garden pitch.