It's a bit of a long story. [ Adrien remarked in a wry tone. ]

In a nutshell, humanity on my version of Earth succeeded in destroying all of Earth's natural resources. All the flora, all the fauna gone. The entire planet was a wasteland, the only naturally surviving organic matter was humanity.

We survived by managing to successfully get out to the stars, other worlds and other species where we slowly built up trade relationships to procure the resources we needed to survive.

[ That really was a nutshell version, but it covered the highlights. ]

So trees are a novelty and I've been told I have to actually mow the stuff they called grass.