Out of Character
The shaft is about six feet long, but the bill originated when a hedging tool was attached to a pole -- so it does have some acquaintance with vegetation. I'll spend some more time with the books, but off the top of my head, mechanically, at most I'd maybe give it -1 in dense forest, but it is a piercing weapon as much as it is a slashing weapon, so you might even be able to avoid even that. Now, would it impede your movement? In really dense forest or foliage, perhaps, but not generally in wooded areas. I'll read some more and see if that point of view changes.