Well, it's a lot of things, including roads, train tracks, sewers, and the power grid. Why did 5 million people lose power during Hurricane Irene? Sometimes because trees fell over and broke the lines leading to their houses. But some people lost power because a tree fell over and broke a line somewhere else and so flummoxed the grid that big sections of it shut down. There is a way to prevent much of that called "smart grid technology." For around half a trillion dollars we could install smart grids across much of the country, which might cut the loss of power in storms in half. Since power failures cost the US economy around $100 billion a year, spending $500 billion to cut that number in half would pay for itself in ten years. Smart grids can also make much better use of some kinds of renewable power, which enter the grid somewhat differently than power from conventional plants.
And here's a more radical idea: bury the power lines underground. It's expensive, but buried lines can't be cut by falling trees, and wouldn't it be great to live in a world where every view isn't cluttered with telephone poles and power lines?