How do you terraform Mars without any trees?
 
Come to think of it, how is there snow on Mars? And where's the water for all these people? And if all the structues belonged to the EDF, what happens after the campaign when the EDF are gone? They're obviously the ones with all the money. How does any of this game make any sense?

Didn't you see Red Planet? You use carnivorous algae bugs to create oxygen.
 
Duh.

It's a game, it doesn't have to make sense.

It is a game about a guy who takes down towers with a sledge hammer.  Any and everything beyond that is trivial.
 
 
But since you asked, trees on Mars look just like rocks, so you see they are actually all over the place, you probably just assumed that they were rocks. :/

I know right, man I just wish we could get a shipment of Martian crystalline aquaberries here on Talon Beta IV...

I think trees would clash with the red planet theme. Red fits "red faction" more than green does, right?

" I think trees would clash with the red planet theme. Red fits "red faction" more than green does, right? "

It's a video game.

" It's a video game. "

You do realize the game does not take place across the entire planet, don't you?  Even then, there is at least grass in the Oasis sector.

 After recalling the evil bastard that he used to be, Douglas Quaid thwarted his one time pal and Mars administrator Vilos Cohaagen, witnessed Michael Ironside's arms get ripped off, and magaged to turn on the ancient Alien atmosphere processor, which filled the Martian atmosphere with oxygen fast enough so he and his new lady friend didn't die of asphyxiation and decompression...

oh wait...    

Who cares?
 
DESTROY THAT BUILDING!

A fundamental concept in ecology is the notion of succession.  

http://en.wikipedia.org/wiki/Ecological_succession
 
 

" I am pretty sure all the oxygen on mars in RFG is made with all the Weed they are growing on the other side of the planet. That area is closed off and secret for obvious reasons...  and yes, all that chronic goes to directly to Still Water gangs... "

 You think too much.

I think it's a fair video game logic question but the game decided to keep the mars aesthetic instead of logic.
 
Planetary ecosystems are shaky to create anyway so making it work through video game logic is every more so.

fuck trees. who needs them? surely we don't. right? 

" fuck trees. who needs them? surely we don't. right?  "

" It's a game, it doesn't have to make sense. "