ID:263134
 
Code:
turf
icon = 'Turf.dmi'
Grass
icon_state = "grass"
Tree01
icon_state = "0,0"
Tree02
icon_state = "1,0"
New()
src.overlays+=/turf/Tree03
..()
Tree03
icon_state = "2,0"
pixel_x = -32


Problem description:
Tree003 does not appear when it is set to -32, but does appear when set to a positive number.

In any way, it'd be best to make trees and such objects. Considering there should only be one turf in a tile.

Objects are best suited for overlays such as plants, flowers, furniture, trees and such things. A turf is just the ground, in a manner of speaking.

O-matic
I feel like I'm plugging this all over the place, but it really does solve alot of multi-tile issues. No, trees do not have to be objects, and it's a bad idea to make them objects if you never intend to move them, but intend to have a lot of them. There is an object limit of 65536, but turfs are only limited by unique instances.

http://developer.byond.com/hub/DerDragon/BigIcons

Give my library a shot. It makes multi-tile atoms a snap.