Earth invaded, conquered & terraformed

Paperback book with a group of people walking on the cover. Publication: 1960s-70s. Earth is invaded and conquered by aliens, who then terraform the planet in order to grow a crop that is crucial to them. The surviving humans hide out. Aliens leave once the crop is harvested. Very few humans remain at the end of the story - kind of depressing.

Maybe The Genocides by Thomas M. Disch. The crop is giant trees, IIRC. I don't see any LT covers with walking people, however.

>2 dukedom_enough: I'm almost certain that is the book. I do recall one of the paperback versions had a cover with people walking through what looked like a green jungle....and yes, it was depressing.

Thanks! After reading a synopsis: http://en.wikipedia.org/wiki/The_Genocides, I can say without doubt that The Genocides is the book I was thinking of. Many thanks!

You're welcome.