That is called weather affect.
In winter & summer, the solid woods contracts or expands depending on their density, coatings, vulnerability to the moisture, etc.
Since its natural hence its inevitable. But there are some ways to prevent it. They called it Seasoning of Wood and there are many ways.
One classic way is to throw the wood stems into water/Chapparr for 6 months at-least and then pull it out and dry it in sun for few months.
Another classic way is to just leave it at open space in sun for 1 year. Let it bear rains, weather dryness, winter, sunshines, etc.
But now most fastest way is KH (Klin Heated). They heat the wood planks and dry their moisture. But again you have to put that wood into sun for couple of days so that it can naturally gain back some of its moisture from air.
