Board Thread:Questions and Answers/@comment-70.31.139.90-20130701230202/@comment-8540798-20130702103046

The Rubber Trees that yield Sticky Resin, are the trees that give you black rubber, so ignore that.

The other Rubber Trees are from Minefactory Reloaded, and if you have the IC2 installed, they won't show up. So you have to enable those in the Config file for MFR. They drop Rubber when you harvest them, and they can be smelted into the orange-brown Rubber Bars. The config you need to enable is this line;

"# Whether or not to generate rubber trees during map generation

B:WorldGen.RubberTree=false"

Change the false to true, and you'll be fine. That line's in the General Section of the file, third from the bottom on the list.

No idea if this will bug your game with the IC2 Rubber Trees appearing as well though.