I abstract this by modifying the map and giving motorized units the ability to enter woods with a very low movement factor. 5% works for me. I toyed with the idea of adding woods and dense woods. They only difference being motorized wouldn't be able to move thru the dense woods.
First off, trying to track fragments would be very difficult and what does it really add in terms of gameplay? Some units may lose their transport and be dismounted for the remainder of the scenario? Not worth the effort imo, just abstract it.
Second, I don't know how forests were in WWII in Europe but in 1990 most were not so dense that we couldn't pick our way thru given enough time. Plus there seemed to be small logging trails everywhere. Again, probably not a good comparison, but, meh, we did it.
As a side not, maybe you should consider changing the unarmed halftracks from the AFV class to the Truck class. From what I read, the men prefered to fight dismounted from the halftracks. I changed it in the ESTAB and the halftracks live much longer. Prior to, they were getting hammered...