It's a desert so trees can't survive without irrigation. Since water is scarce as well, there aren't enough trees to cover the vast low density area.

You can always start small and over decades grow the area. After all that is how cities like Copenhagen and Amsterdam became bike friendly, not just a few years, but decades of work.

What about https://en.wikipedia.org/wiki/Dracaena_cinnabari or https://en.wikipedia.org/wiki/Chilopsis?