I understand the theme, with Durthu being a count-as Coeddill? All very cool and well themed. There are a few things i'd suggest to make the army flow better, but i won't suggest anything that breaks the theme.
You should drop the strangle roots off of the Ancient (
Bs 4 just isn't worth the 20pt investment) and a single Dryad from the Wildwood Sisterhood. Drycha needs a place to stay and you don't want her hanging off the end of a unit, and placing her in this unit makes the most fluff sense.
Finally i would suggest you get your hands on some Wild Riders. Hear me out, a friend of mine has created some spectacular Wild Riders by greenstuffing Dryad upper bodies onto the necks of horses to make Dryad Centaurs. They looked great. Wild Riders rules basically emulate forest spirits (ItP and 6+ ward save) and they add some much needed punch to your army. Dryads and Treemen and Treekin and hold up an enemy fine, but have trouble grinding through them. Having a unit of Dryad Centaurs thrown into the flank of a combat will help you massively.
I'd suggest trying to fit in 2 units of 6 with Champions. These are not my friends models, but this is where he stole the idea from. Would something like this appeal to you?