Trees from Project Red seem to be spawning in Aroma1997's mining dimension. This dimension is specifically designed for mining purposes: flat surface, no mobs, always day, no trees.

The trees spawn using Project Red 4.0.5 build 12 with Aroma1997Core 1.0.1.0 and Aroma1997s Dimensional World 1.0.2.11

Link to Aroma1997s forum page:
http://www.minecraftforum.net/topic/1679684-

Screenshot of trees in mining world:
http://i43.tinypic.com/28iooat.png

Fixed via 38c923f