eli5: How do trees get bigger? What’s physically happening to them?
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On a large scale, trees grow from the ends of their branches, and they slowly get fatter all around. The branches, trunk, and roots all get wider, but the ends of each also get longer.
The microscopic version is the same as any other living thing. Cells divide and the living thing gets bigger. At the tips of branches are areas called meristems, where new growth happens. Cells divide and add on to the end of the branch to get longer each year.
The same general idea is happening under the bark in an area called the vascular cambium. This area is where all the new cells divide and it sits in between two layers of the tree called xylem and phloem. Xylem is further towards the center and moves water through the tree. Phloem is just under the bark and moves sugars and other plant food. The cambium makes new cells for the xylem and the phloem and the tree gets wider. Ever look at the rings of a cut down tree? The rings occur because in the Spring, the tree is growing quickly, and the cells aren’t packed as close together as they form. In the late Fall and Winter, they slow down on growth, and the cells being formed pack closer together, making a dark ring each year
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