To fight in forrests was dificult yesterday and now a days too! Take a look on Vietinã war to remember that...
My advice is:
Put your infantry in loose formation and attack them like animals! try to flank them with your cavalary or round the enemy lines and attack them behind.
Use this formation to enter in a forrest:
10 heavy infantry, prefer swordman units to spearman;
5 light infantry or spearmans;
4 heavy cavalary;
1 General.

In a jungle, fight like animal, defensive formations or organized attack don't work like in open fields.