The rubber tree is used to collect [Resin] which can be used to make Rubber, a very important component of many IndustrialCraft recipes you need it when you first begin your world. Bone meal will not work on Rubbertree Saplings.
You can identify a rubber tree by its darker wood, lighter leaves, orange-brown rectangles on the sides, or by the distinctive 3 leaf protrusion upwards from the top wood block.
Rubber WoodEditRubber wood can be placed into a extractor which will then turn each wood block into a piece of rubber. This is a far more efficient way of gathering rubber as you dont have to wait for the resin deposits to respawn and you can just replant the tree from the saplings it drops. The giant rubber trees wood also works exactly the same.
Giant Rubber TreeEdit
There are also giant rubber trees like the one in the picture. These trees are added by RedPower 2, not IndustrialCraft, and aren't fully implemented yet. They don't have any resin deposits.
If place in a industrialcraft extractor they will give you 1 rubber but it's just better to convert it into emc.
- Even if you're playing on Fast, the leaves have a transparant texture. (fixed?)