Latest release of the mod, 0.8.1e for 1.12.2, and last recommended forge version, 14.23.4.2705.
When attempting to chop down the a tree with the new falling feature there's a very loud noise caused by the breaking of several leaf blocks. This brings also lag to the world. I'm usually run smoothly at 50-60 fps without problems, but in the moment the log block is broken and the falling event starts the fps dropped down a lot around 10-20, once even at less than 10 fps, and then return to normal once the animation of the falling starts.
I replicated the issue using only DynamicTrees.
I know this probably just needs some optimization for the lag, since it's a feature in alpha, but I think the most annoying thing is the breaking leaf noise when you chop down the tree.

It's probably the multiplicity of leaf block breaking sounds and the thousands of leaf particles that spawn that cause the lag. I'll look into it.

Shame on me, I normally develop the mod with the sound turned down because I'm listening to music. :)

Fixed in dev