Technically the land under the power lines is the utility right-of-way. The utility has an easement so they essentially own it. How much land on either side of the pole they own varies based on a bunch of factors. The main goal is to keep trees from growing close to the lines because they can short out the phases if the branches come in contact with them.

The voltage on the lines in OP’s photo probably isn’t that high since at least some of them are distribution lines. If you go to a substation where you’re in close proximity to the transmission lines that come from the power plant, those can be well into the hundreds of thousands of volts. They can literally make your hair stand on end. When the weather is just right, you can hear the static electricity in the air crackling around them. It’s freaky.

Source: Used to work in utilities.