The reason is that the south is sunny, and the sunshine and rain are richer than the shady side facing north, so the trees facing south get more nutrients and grow stronger, so the rings are sparse.
In the same way, the north side is shaded, and the nutrients in the south are not fully absorbed, so the annual rings are dense? .
Extended data:
Tree rings are the annual changes of cells and vessels in trees from large to small and substances from loose to dense, thus forming rings of different colors and textures.
Tree rings are produced by the annual activities of the cambium. The mild climate and abundant rainfall in spring are beneficial to the growth of trees. This is because the cambium cells divide vigorously, the newborn cells are large and obvious, and the ducts are large and many. Therefore, the wood looks light in color and soft in texture. After summer, as the temperature rises. Rainfall decreases, especially in autumn, the weather is getting colder and colder, the rainfall is less, the cambium activity is weakened, and the shape of splinter cell becomes smaller. In addition, the cell wall is thick and there are few ducts, so the wood looks dense and hard, and the color is dark.
Tree rings represent the periodic changes in the growth environment of trees, usually followed by an annual change cycle, so tree rings also represent the growth in a year. According to the tree rings, we can infer the age of trees, which can be used to examine the age of forests.
References:
Tree rings-Baidu Encyclopedia