This question is one that I asked to my science teacher when I was little, only to be greeted with the discouraging answer of “What did you expect them to have”. However I will do my best to explain this phenomenon better than her to you! First reason of this phenomenon is to increase the surface area to absorb more photons(light) from the sun. This is analogous to the fact that bigger roof means more rain on it. Second reason is to reach out to bigger areas to increase the availability of resources. Third reason is to have a more stable and flexible structure. If the tree did not have branches and was a long trunk, when faced with a wind it would have to stand the entire wind with a small cross-sectional area. When you have branches and have a force on one point, the branch bends to focus the force on a larger area (this is done by increasing the angle the branch makes with respect to the y axis. This increment is done with the torque of the wind that is free to be exerted since the branch is hanging , therefor decreasing the pressure. That is the reason why trees’ branches provide structural support. Also another reason for their stability with relative to a T like trunk is that if you concentrate weight on farther locations, torque by gravity will be higher and the structure will be less stable! This is reasoned by torque being proportional to force times the radius with respect to the axis of rotation. When weight increases in distant areas, so does the torque, more than it would have increased if the weight was closer to the axis of rotation.
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