Land might be scarce in the technical sense, but not in the practical sense. Housing is only expensive because people want to live in superstar cities, which in turn is because that's where all the jobs are. If UBI eliminates the imperative to live in superstar cities, that makes scarcity a non-issue.

I can work from anywhere, but I like to live in a superstar city because I find it boring living in the suburbs. I want to be near my friends, near the live events, near the buzzing restaurants and art galleries and clothing stores where I can walk around and touch things. There will always be a concentration of people in cities for these reasons.

Just need UBI, unlike all other forms of marginal increases in income, to spur people to move away from cities rather than towards them.