A model with this special rule has the Forest Strider special rule. In addition, if at least half of the models in a unit are within a forest:
All models in that unit that have the Forest stalker special rule fire in one more rank than normal (if the unit chooses to Volley Fire, this will normally mean that all the models in the front three ranks, and half the models in the fourth and any subsequent ranks, are allowed to shoot).
All models in that unit that have the Forest Stalker special rule can make supporting attacks with one extra rank than normal. This is cumulative with other special rules that allow models to fight in extra ranks.
All models in that unit that have the Forest Stalker special rule (but not their mounts) re-roll all To Wound rolls of a 1 when making close combat attacks.