Watch out, Timber! Hitting the bottom block of the tree with an axe of any type, you may make all the logs in a tree break. To toggle this effect, you can hold down C while chopping logs with your axe in order to safely remove logs(configurable in /.minecraft/config/mod_Timber.cfg).
Axes added by other mods will not work by default, you will have to edit the Timber! config file (see above) and add the ids for the mod axes manually. The ids for the vanilla axes and the PlasticCraft axe is included by default.