Trees and robots - I want it all

Science publishes data on tree mortality rates. Emily Chang writes about robot density.

I decide, somewhat foolishly, that I want to correlate data on trees-per-capita with robots-per-capita. Fail miserably. And not through my lack of effort - I just can't find data that breaks down the trees by geography.

The closest I can get is that we have more trees per capita (61) than robots per capita (less than 61). Makes sense I guess.

If somebody can point me in the direction of the appropriate data, I'll do the hard work and credit you graciously.