This explains it better than I could:
Quick one sentence summary: Using totems below the wood you normally whittle now has a massive experience penalty.
Totems offer awesome experience and were intended to be a rare but extremely helpful event. The biggest problem with the old totem system, that higher level players could quickly craft low level totems and use them as a training method to get millions of forestry experience. To reduce using totems not around your level, an experience penalty has been added.
How it works (warning math): Look at your whittling and forestry skills with what ever buffs you currently have, pick the higher one. The highest skill is then divided by 25, round down. This is the tree level that the game thinks you should be working on, at the minimum. Using totems of this level or higher, have no change. Totems below that level get an experience penalty that fits this formula, Normal Experience * (1 - (TreeLevel - Totemlevel)^2/TreeLevel)). At the minimum, you get at least 10% of the normal experience.
This change is already in the code. Hopefully this prevents any abuse of low level totems but keeps ones that match your level awesome.